From patchwork Thu Dec 5 16:09:18 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 13895692 Received: from smtp-190d.mail.infomaniak.ch (smtp-190d.mail.infomaniak.ch [185.125.25.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A2BA6221463 for ; Thu, 5 Dec 2024 16:09:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.125.25.13 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733414998; cv=none; b=fCyDFwCv5RAhl4v7v6fckte/W6xherOxpklRHM/wDwcM9ZrkBQ1W2DsJgLdFhK0+nQIsCPB3XoJ//Vs9z8qO3T1riPNHlZYK9LxOGcCdK0jA6BVUFKN0uI9F7Qq9dtHxgjJbUAlDCJfqP8bytDUrG5XuKAeMb/b5ioigVZMlIiI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733414998; c=relaxed/simple; bh=RP85EB0JPMxqBe9enzwWtSmpSe9gECP9CorwqIMc/jU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=OrBf7B811YvBZFXbHtrsU1iqm05/d2ynx/ic5WKqH/fgO5kEXwfmWGd7ZjL2wjj2ewGpnqHncSkD/3OUBo5C27qeSut4cxGUQIJ0i6/0lnjfMg7/buTuICQ5hp+hmg0oSd3VSUINIGqB4nI+E8seIhupbx00Lb9ELfoftqCS9Kg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net; spf=pass smtp.mailfrom=digikod.net; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b=fivtcfl6; arc=none smtp.client-ip=185.125.25.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=digikod.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b="fivtcfl6" Received: from smtp-4-0001.mail.infomaniak.ch (unknown [IPv6:2001:1600:7:10:40ca:feff:fe05:1]) by smtp-4-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4Y3zqb32ltzssH; Thu, 5 Dec 2024 17:09:47 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1733414987; bh=Rv90cIm/DfvkuDs5cYfIFc/UTRHBVaOslMZuoqNbp/U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fivtcfl6qWtPX2O10RcYAzlHarGWmBxDa9vaHgRXb+wRdYoRto6diK8n634EFoYRJ N6e9ds1l1nrIjM8Z9V6bmf7jzl/DoA0wk2G62WqgMC2piyJ/F5ZyTmw/9LWkv0TaxL cVvkkTwGEpRn4LSAB7wbpmOxDvuNKJ+V5+++aE7A= Received: from unknown by smtp-4-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4Y3zqZ3Kdfzg63; Thu, 5 Dec 2024 17:09:46 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Al Viro , Christian Brauner , Kees Cook , Paul Moore , Serge Hallyn Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Adhemerval Zanella Netto , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Elliott Hughes , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Linus Torvalds , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH v22 1/8] exec: Add a new AT_EXECVE_CHECK flag to execveat(2) Date: Thu, 5 Dec 2024 17:09:18 +0100 Message-ID: <20241205160925.230119-2-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha Add a new AT_EXECVE_CHECK flag to execveat(2) to check if a file would be allowed for execution. The main use case is for script interpreters and dynamic linkers to check execution permission according to the kernel's security policy. Another use case is to add context to access logs e.g., which script (instead of interpreter) accessed a file. As any executable code, scripts could also use this check [1]. This is different from faccessat(2) + X_OK which only checks a subset of access rights (i.e. inode permission and mount options for regular files), but not the full context (e.g. all LSM access checks). The main use case for access(2) is for SUID processes to (partially) check access on behalf of their caller. The main use case for execveat(2) + AT_EXECVE_CHECK is to check if a script execution would be allowed, according to all the different restrictions in place. Because the use of AT_EXECVE_CHECK follows the exact kernel semantic as for a real execution, user space gets the same error codes. An interesting point of using execveat(2) instead of openat2(2) is that it decouples the check from the enforcement. Indeed, the security check can be logged (e.g. with audit) without blocking an execution environment not yet ready to enforce a strict security policy. LSMs can control or log execution requests with security_bprm_creds_for_exec(). However, to enforce a consistent and complete access control (e.g. on binary's dependencies) LSMs should restrict file executability, or measure executed files, with security_file_open() by checking file->f_flags & __FMODE_EXEC. Because AT_EXECVE_CHECK is dedicated to user space interpreters, it doesn't make sense for the kernel to parse the checked files, look for interpreters known to the kernel (e.g. ELF, shebang), and return ENOEXEC if the format is unknown. Because of that, security_bprm_check() is never called when AT_EXECVE_CHECK is used. It should be noted that script interpreters cannot directly use execveat(2) (without this new AT_EXECVE_CHECK flag) because this could lead to unexpected behaviors e.g., `python script.sh` could lead to Bash being executed to interpret the script. Unlike the kernel, script interpreters may just interpret the shebang as a simple comment, which should not change for backward compatibility reasons. Because scripts or libraries files might not currently have the executable permission set, or because we might want specific users to be allowed to run arbitrary scripts, the following patch provides a dynamic configuration mechanism with the SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE securebits. This is a redesign of the CLIP OS 4's O_MAYEXEC: https://github.com/clipos-archive/src_platform_clip-patches/blob/f5cb330d6b684752e403b4e41b39f7004d88e561/1901_open_mayexec.patch This patch has been used for more than a decade with customized script interpreters. Some examples can be found here: https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC Cc: Al Viro Cc: Christian Brauner Cc: Kees Cook Acked-by: Paul Moore Reviewed-by: Serge Hallyn Link: https://docs.python.org/3/library/io.html#io.open_code [1] Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-2-mic@digikod.net Reviewed-by: Jeff Xu < jeffxu@chromium.org> Tested-by: Jeff Xu --- Changes since v21: * Remove the audit changes, requested by Paul. * Add Acked-by: Paul Moore. * Fix a typo in comments and in commit message. * Add SPDX-License-Identifier header to the documentation. * Rebase on v6.13-rc1 . Changes since v20: * Rename AT_CHECK to AT_EXECVE_CHECK, requested by Amir Goldstein and Serge Hallyn. * Move the UAPI documentation to a dedicated RST file. * Add Reviewed-by: Serge Hallyn Changes since v19: * Remove mention of "role transition" as suggested by Andy. * Highlight the difference between security_bprm_creds_for_exec() and the __FMODE_EXEC check for LSMs (in commit message and LSM's hooks) as discussed with Jeff. * Improve documentation both in UAPI comments and kernel comments (requested by Kees). New design since v18: https://lore.kernel.org/r/20220104155024.48023-3-mic@digikod.net --- Documentation/userspace-api/check_exec.rst | 37 ++++++++++++++++++++++ Documentation/userspace-api/index.rst | 1 + fs/exec.c | 20 ++++++++++-- include/linux/binfmts.h | 7 +++- include/uapi/linux/fcntl.h | 4 +++ security/security.c | 10 ++++++ 6 files changed, 76 insertions(+), 3 deletions(-) create mode 100644 Documentation/userspace-api/check_exec.rst diff --git a/Documentation/userspace-api/check_exec.rst b/Documentation/userspace-api/check_exec.rst new file mode 100644 index 000000000000..393dd7ca19c4 --- /dev/null +++ b/Documentation/userspace-api/check_exec.rst @@ -0,0 +1,37 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright © 2024 Microsoft Corporation + +=================== +Executability check +=================== + +AT_EXECVE_CHECK +=============== + +Passing the ``AT_EXECVE_CHECK`` flag to :manpage:`execveat(2)` only performs a +check on a regular file and returns 0 if execution of this file would be +allowed, ignoring the file format and then the related interpreter dependencies +(e.g. ELF libraries, script's shebang). + +Programs should always perform this check to apply kernel-level checks against +files that are not directly executed by the kernel but passed to a user space +interpreter instead. All files that contain executable code, from the point of +view of the interpreter, should be checked. However the result of this check +should only be enforced according to ``SECBIT_EXEC_RESTRICT_FILE`` or +``SECBIT_EXEC_DENY_INTERACTIVE.``. + +The main purpose of this flag is to improve the security and consistency of an +execution environment to ensure that direct file execution (e.g. +``./script.sh``) and indirect file execution (e.g. ``sh script.sh``) lead to +the same result. For instance, this can be used to check if a file is +trustworthy according to the caller's environment. + +In a secure environment, libraries and any executable dependencies should also +be checked. For instance, dynamic linking should make sure that all libraries +are allowed for execution to avoid trivial bypass (e.g. using ``LD_PRELOAD``). +For such secure execution environment to make sense, only trusted code should +be executable, which also requires integrity guarantees. + +To avoid race conditions leading to time-of-check to time-of-use issues, +``AT_EXECVE_CHECK`` should be used with ``AT_EMPTY_PATH`` to check against a +file descriptor instead of a path. diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index 274cc7546efc..6272bcf11296 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -35,6 +35,7 @@ Security-related interfaces mfd_noexec spec_ctrl tee + check_exec Devices and I/O =============== diff --git a/fs/exec.c b/fs/exec.c index 98cb7ba9983c..e3f461096e84 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -892,7 +892,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) .lookup_flags = LOOKUP_FOLLOW, }; - if ((flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0) + if ((flags & + ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH | AT_EXECVE_CHECK)) != 0) return ERR_PTR(-EINVAL); if (flags & AT_SYMLINK_NOFOLLOW) open_exec_flags.lookup_flags &= ~LOOKUP_FOLLOW; @@ -1541,6 +1542,21 @@ static struct linux_binprm *alloc_bprm(int fd, struct filename *filename, int fl } bprm->interp = bprm->filename; + /* + * At this point, security_file_open() has already been called (with + * __FMODE_EXEC) and access control checks for AT_EXECVE_CHECK will + * stop just after the security_bprm_creds_for_exec() call in + * bprm_execve(). Indeed, the kernel should not try to parse the + * content of the file with exec_binprm() nor change the calling + * thread, which means that the following security functions will not + * be called: + * - security_bprm_check() + * - security_bprm_creds_from_file() + * - security_bprm_committing_creds() + * - security_bprm_committed_creds() + */ + bprm->is_check = !!(flags & AT_EXECVE_CHECK); + retval = bprm_mm_init(bprm); if (!retval) return bprm; @@ -1836,7 +1852,7 @@ static int bprm_execve(struct linux_binprm *bprm) /* Set the unchanging part of bprm->cred */ retval = security_bprm_creds_for_exec(bprm); - if (retval) + if (retval || bprm->is_check) goto out; retval = exec_binprm(bprm); diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index e6c00e860951..8ff0eb3644a1 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -42,7 +42,12 @@ struct linux_binprm { * Set when errors can no longer be returned to the * original userspace. */ - point_of_no_return:1; + point_of_no_return:1, + /* + * Set by user space to check executability according to the + * caller's environment. + */ + is_check:1; struct file *executable; /* Executable to pass to the interpreter */ struct file *interpreter; struct file *file; diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 6e6907e63bfc..a15ac2fa4b20 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -155,4 +155,8 @@ #define AT_HANDLE_MNT_ID_UNIQUE 0x001 /* Return the u64 unique mount ID. */ #define AT_HANDLE_CONNECTABLE 0x002 /* Request a connectable file handle */ +/* Flags for execveat2(2). */ +#define AT_EXECVE_CHECK 0x10000 /* Only perform a check if execution + would be allowed. */ + #endif /* _UAPI_LINUX_FCNTL_H */ diff --git a/security/security.c b/security/security.c index 09664e09fec9..dae7e903947f 100644 --- a/security/security.c +++ b/security/security.c @@ -1248,6 +1248,12 @@ int security_vm_enough_memory_mm(struct mm_struct *mm, long pages) * to 1 if AT_SECURE should be set to request libc enable secure mode. @bprm * contains the linux_binprm structure. * + * If execveat(2) is called with the AT_EXECVE_CHECK flag, bprm->is_check is + * set. The result must be the same as without this flag even if the execution + * will never really happen and @bprm will always be dropped. + * + * This hook must not change current->cred, only @bprm->cred. + * * Return: Returns 0 if the hook is successful and permission is granted. */ int security_bprm_creds_for_exec(struct linux_binprm *bprm) @@ -3098,6 +3104,10 @@ int security_file_receive(struct file *file) * Save open-time permission checking state for later use upon file_permission, * and recheck access if anything has changed since inode_permission. * + * We can check if a file is opened for execution (e.g. execve(2) call), either + * directly or indirectly (e.g. ELF's ld.so) by checking file->f_flags & + * __FMODE_EXEC . + * * Return: Returns 0 if permission is granted. */ int security_file_open(struct file *file) From patchwork Thu Dec 5 16:09:19 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 13895694 Received: from smtp-8fac.mail.infomaniak.ch (smtp-8fac.mail.infomaniak.ch [83.166.143.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 73509222565 for ; Thu, 5 Dec 2024 16:09:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=83.166.143.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733415000; cv=none; b=NsiPwN+yuHA7QebrqNarj0nwRGyI25dnkys1kElwtYTUyVhpC16DgkTunFCTpdUcqKEiAswFFhdvfis71xiN1iMekHx5rU/4T1O2l0VA/fFLnH4xLbTN+WJj9b6ClPZDqUjSAPvYEJLqT0JFdUAssQW1N6y0homDnw2pc8kKaxY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733415000; c=relaxed/simple; bh=WmWOCdkjKo6MtTVnA872qhYHCQ59oQc2/lgIqJziF+I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=SQEa6qfDbCX84T6Jw5q4BurUty1hx9ZgkHQPd6O9bS80QsSOSi+Mf+E2/7OvWkfeWulL692iB5zxCPMSXyERycWvU6VxnxGsF+lzNgg/wl7xmV51Dzb2FkqjFAadAuvhSPxcQq3JHwZ+1/gzFackHYCM/4w3FAXDs12ALHid2Lc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net; spf=pass smtp.mailfrom=digikod.net; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b=EgMs5f3y; arc=none smtp.client-ip=83.166.143.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=digikod.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b="EgMs5f3y" Received: from smtp-3-0000.mail.infomaniak.ch (smtp-3-0000.mail.infomaniak.ch [10.4.36.107]) by smtp-3-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4Y3zqd2SpFz7fp; Thu, 5 Dec 2024 17:09:49 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1733414989; bh=2JHrvFj52PIr/gUI8lbelcyTiQ9XLMHaAN+1bWUHYBo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EgMs5f3yrTfqExqspH03ei1/z9wJtsjIcMUutDNpb/QcLhr+oemXaaSUN2JED2L5j WFF0bESSg4g16rGPAgeoq4QkP1ShC9U2DZ4X6CTOlysHdMswdSbAijrimXAUeCbIiB 8kXiDV1Z5Yb2l99un/wzvSxNT5R5ep/hMWW0GwBA= Received: from unknown by smtp-3-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 4Y3zqb6l5Vzdgm; Thu, 5 Dec 2024 17:09:47 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Al Viro , Christian Brauner , Kees Cook , Paul Moore , Serge Hallyn Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Adhemerval Zanella Netto , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Elliott Hughes , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Linus Torvalds , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Andy Lutomirski Subject: [PATCH v22 2/8] security: Add EXEC_RESTRICT_FILE and EXEC_DENY_INTERACTIVE securebits Date: Thu, 5 Dec 2024 17:09:19 +0100 Message-ID: <20241205160925.230119-3-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha The new SECBIT_EXEC_RESTRICT_FILE, SECBIT_EXEC_DENY_INTERACTIVE, and their *_LOCKED counterparts are designed to be set by processes setting up an execution environment, such as a user session, a container, or a security sandbox. Unlike other securebits, these ones can be set by unprivileged processes. Like seccomp filters or Landlock domains, the securebits are inherited across processes. When SECBIT_EXEC_RESTRICT_FILE is set, programs interpreting code should control executable resources according to execveat(2) + AT_EXECVE_CHECK (see previous commit). When SECBIT_EXEC_DENY_INTERACTIVE is set, a process should deny execution of user interactive commands (which excludes executable regular files). Being able to configure each of these securebits enables system administrators or owner of image containers to gradually validate the related changes and to identify potential issues (e.g. with interpreter or audit logs). It should be noted that unlike other security bits, the SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE bits are dedicated to user space willing to restrict itself. Because of that, they only make sense in the context of a trusted environment (e.g. sandbox, container, user session, full system) where the process changing its behavior (according to these bits) and all its parent processes are trusted. Otherwise, any parent process could just execute its own malicious code (interpreting a script or not), or even enforce a seccomp filter to mask these bits. Such a secure environment can be achieved with an appropriate access control (e.g. mount's noexec option, file access rights, LSM policy) and an enlighten ld.so checking that libraries are allowed for execution e.g., to protect against illegitimate use of LD_PRELOAD. Ptrace restrictions according to these securebits would not make sense because of the processes' trust assumption. Scripts may need some changes to deal with untrusted data (e.g. stdin, environment variables), but that is outside the scope of the kernel. See chromeOS's documentation about script execution control and the related threat model: https://www.chromium.org/chromium-os/developer-library/guides/security/noexec-shell-scripts/ Cc: Al Viro Cc: Andy Lutomirski Cc: Christian Brauner Cc: Kees Cook Cc: Paul Moore Reviewed-by: Serge Hallyn Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-3-mic@digikod.net Reviewed-by: Jeff Xu < jeffxu@chromium.org> Tested-by: Jeff Xu --- Changes since v21: * Extend user documentation with exception regarding tailored execution environments (e.g. chromeOS's libc) as discussed with Jeff. Changes since v20: * Move UAPI documentation to a dedicated RST file and format it. Changes since v19: * Replace SECBIT_SHOULD_EXEC_CHECK and SECBIT_SHOULD_EXEC_RESTRICT with SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE: https://lore.kernel.org/all/20240710.eiKohpa4Phai@digikod.net/ * Remove the ptrace restrictions, suggested by Andy. * Improve documentation according to the discussion with Jeff. New design since v18: https://lore.kernel.org/r/20220104155024.48023-3-mic@digikod.net --- Documentation/userspace-api/check_exec.rst | 107 +++++++++++++++++++++ include/uapi/linux/securebits.h | 24 ++++- security/commoncap.c | 29 ++++-- 3 files changed, 153 insertions(+), 7 deletions(-) diff --git a/Documentation/userspace-api/check_exec.rst b/Documentation/userspace-api/check_exec.rst index 393dd7ca19c4..05dfe3b56f71 100644 --- a/Documentation/userspace-api/check_exec.rst +++ b/Documentation/userspace-api/check_exec.rst @@ -5,6 +5,31 @@ Executability check =================== +The ``AT_EXECVE_CHECK`` :manpage:`execveat(2)` flag, and the +``SECBIT_EXEC_RESTRICT_FILE`` and ``SECBIT_EXEC_DENY_INTERACTIVE`` securebits +are intended for script interpreters and dynamic linkers to enforce a +consistent execution security policy handled by the kernel. See the +`samples/check-exec/inc.c`_ example. + +Whether an interpreter should check these securebits or not depends on the +security risk of running malicious scripts with respect to the execution +environment, and whether the kernel can check if a script is trustworthy or +not. For instance, Python scripts running on a server can use arbitrary +syscalls and access arbitrary files. Such interpreters should then be +enlighten to use these securebits and let users define their security policy. +However, a JavaScript engine running in a web browser should already be +sandboxed and then should not be able to harm the user's environment. + +Script interpreters or dynamic linkers built for tailored execution environments +(e.g. hardened Linux distributions or hermetic container images) could use +``AT_EXECVE_CHECK`` without checking the related securebits if backward +compatibility is handled by something else (e.g. atomic update ensuring that +all legitimate libraries are allowed to be executed). It is then recommended +for script interpreters and dynamic linkers to check the securebits at run time +by default, but also to provide the ability for custom builds to behave like if +``SECBIT_EXEC_RESTRICT_FILE`` or ``SECBIT_EXEC_DENY_INTERACTIVE`` were always +set to 1 (i.e. always enforce restrictions). + AT_EXECVE_CHECK =============== @@ -35,3 +60,85 @@ be executable, which also requires integrity guarantees. To avoid race conditions leading to time-of-check to time-of-use issues, ``AT_EXECVE_CHECK`` should be used with ``AT_EMPTY_PATH`` to check against a file descriptor instead of a path. + +SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE +========================================================== + +When ``SECBIT_EXEC_RESTRICT_FILE`` is set, a process should only interpret or +execute a file if a call to :manpage:`execveat(2)` with the related file +descriptor and the ``AT_EXECVE_CHECK`` flag succeed. + +This secure bit may be set by user session managers, service managers, +container runtimes, sandboxer tools... Except for test environments, the +related ``SECBIT_EXEC_RESTRICT_FILE_LOCKED`` bit should also be set. + +Programs should only enforce consistent restrictions according to the +securebits but without relying on any other user-controlled configuration. +Indeed, the use case for these securebits is to only trust executable code +vetted by the system configuration (through the kernel), so we should be +careful to not let untrusted users control this configuration. + +However, script interpreters may still use user configuration such as +environment variables as long as it is not a way to disable the securebits +checks. For instance, the ``PATH`` and ``LD_PRELOAD`` variables can be set by +a script's caller. Changing these variables may lead to unintended code +executions, but only from vetted executable programs, which is OK. For this to +make sense, the system should provide a consistent security policy to avoid +arbitrary code execution e.g., by enforcing a write xor execute policy. + +When ``SECBIT_EXEC_DENY_INTERACTIVE`` is set, a process should never interpret +interactive user commands (e.g. scripts). However, if such commands are passed +through a file descriptor (e.g. stdin), its content should be interpreted if a +call to :manpage:`execveat(2)` with the related file descriptor and the +``AT_EXECVE_CHECK`` flag succeed. + +For instance, script interpreters called with a script snippet as argument +should always deny such execution if ``SECBIT_EXEC_DENY_INTERACTIVE`` is set. + +This secure bit may be set by user session managers, service managers, +container runtimes, sandboxer tools... Except for test environments, the +related ``SECBIT_EXEC_DENY_INTERACTIVE_LOCKED`` bit should also be set. + +Here is the expected behavior for a script interpreter according to combination +of any exec securebits: + +1. ``SECBIT_EXEC_RESTRICT_FILE=0`` and ``SECBIT_EXEC_DENY_INTERACTIVE=0`` + + Always interpret scripts, and allow arbitrary user commands (default). + + No threat, everyone and everything is trusted, but we can get ahead of + potential issues thanks to the call to :manpage:`execveat(2)` with + ``AT_EXECVE_CHECK`` which should always be performed but ignored by the + script interpreter. Indeed, this check is still important to enable systems + administrators to verify requests (e.g. with audit) and prepare for + migration to a secure mode. + +2. ``SECBIT_EXEC_RESTRICT_FILE=1`` and ``SECBIT_EXEC_DENY_INTERACTIVE=0`` + + Deny script interpretation if they are not executable, but allow + arbitrary user commands. + + The threat is (potential) malicious scripts run by trusted (and not fooled) + users. That can protect against unintended script executions (e.g. ``sh + /tmp/*.sh``). This makes sense for (semi-restricted) user sessions. + +3. ``SECBIT_EXEC_RESTRICT_FILE=0`` and ``SECBIT_EXEC_DENY_INTERACTIVE=1`` + + Always interpret scripts, but deny arbitrary user commands. + + This use case may be useful for secure services (i.e. without interactive + user session) where scripts' integrity is verified (e.g. with IMA/EVM or + dm-verity/IPE) but where access rights might not be ready yet. Indeed, + arbitrary interactive commands would be much more difficult to check. + +4. ``SECBIT_EXEC_RESTRICT_FILE=1`` and ``SECBIT_EXEC_DENY_INTERACTIVE=1`` + + Deny script interpretation if they are not executable, and also deny + any arbitrary user commands. + + The threat is malicious scripts run by untrusted users (but trusted code). + This makes sense for system services that may only execute trusted scripts. + +.. Links +.. _samples/check-exec/inc.c: + https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/check-exec/inc.c diff --git a/include/uapi/linux/securebits.h b/include/uapi/linux/securebits.h index d6d98877ff1a..3fba30dbd68b 100644 --- a/include/uapi/linux/securebits.h +++ b/include/uapi/linux/securebits.h @@ -52,10 +52,32 @@ #define SECBIT_NO_CAP_AMBIENT_RAISE_LOCKED \ (issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE_LOCKED)) +/* See Documentation/userspace-api/check_exec.rst */ +#define SECURE_EXEC_RESTRICT_FILE 8 +#define SECURE_EXEC_RESTRICT_FILE_LOCKED 9 /* make bit-8 immutable */ + +#define SECBIT_EXEC_RESTRICT_FILE (issecure_mask(SECURE_EXEC_RESTRICT_FILE)) +#define SECBIT_EXEC_RESTRICT_FILE_LOCKED \ + (issecure_mask(SECURE_EXEC_RESTRICT_FILE_LOCKED)) + +/* See Documentation/userspace-api/check_exec.rst */ +#define SECURE_EXEC_DENY_INTERACTIVE 10 +#define SECURE_EXEC_DENY_INTERACTIVE_LOCKED 11 /* make bit-10 immutable */ + +#define SECBIT_EXEC_DENY_INTERACTIVE \ + (issecure_mask(SECURE_EXEC_DENY_INTERACTIVE)) +#define SECBIT_EXEC_DENY_INTERACTIVE_LOCKED \ + (issecure_mask(SECURE_EXEC_DENY_INTERACTIVE_LOCKED)) + #define SECURE_ALL_BITS (issecure_mask(SECURE_NOROOT) | \ issecure_mask(SECURE_NO_SETUID_FIXUP) | \ issecure_mask(SECURE_KEEP_CAPS) | \ - issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE)) + issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE) | \ + issecure_mask(SECURE_EXEC_RESTRICT_FILE) | \ + issecure_mask(SECURE_EXEC_DENY_INTERACTIVE)) #define SECURE_ALL_LOCKS (SECURE_ALL_BITS << 1) +#define SECURE_ALL_UNPRIVILEGED (issecure_mask(SECURE_EXEC_RESTRICT_FILE) | \ + issecure_mask(SECURE_EXEC_DENY_INTERACTIVE)) + #endif /* _UAPI_LINUX_SECUREBITS_H */ diff --git a/security/commoncap.c b/security/commoncap.c index cefad323a0b1..52ea01acb453 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -1302,21 +1302,38 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3, & (old->securebits ^ arg2)) /*[1]*/ || ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/ || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/ - || (cap_capable(current_cred(), - current_cred()->user_ns, - CAP_SETPCAP, - CAP_OPT_NONE) != 0) /*[4]*/ /* * [1] no changing of bits that are locked * [2] no unlocking of locks * [3] no setting of unsupported bits - * [4] doing anything requires privilege (go read about - * the "sendmail capabilities bug") */ ) /* cannot change a locked bit */ return -EPERM; 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Thu, 5 Dec 2024 17:09:49 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Al Viro , Christian Brauner , Kees Cook , Paul Moore , Serge Hallyn Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Adhemerval Zanella Netto , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Elliott Hughes , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Linus Torvalds , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH v22 3/8] selftests/exec: Add 32 tests for AT_EXECVE_CHECK and exec securebits Date: Thu, 5 Dec 2024 17:09:20 +0100 Message-ID: <20241205160925.230119-4-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha Test that checks performed by execveat(..., AT_EXECVE_CHECK) are consistent with noexec mount points and file execute permissions. Test that SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE are inherited by child processes and that they can be pinned with the appropriate SECBIT_EXEC_RESTRICT_FILE_LOCKED and SECBIT_EXEC_DENY_INTERACTIVE_LOCKED bits. Cc: Al Viro Cc: Christian Brauner Cc: Kees Cook Cc: Paul Moore Cc: Serge Hallyn Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-4-mic@digikod.net --- Changes since v21: * Fix test's variants formatting. Changes since v20: * Rename AT_CHECK to AT_EXECVE_CHECK. Changes since v19: * Rename securebits. * Rename test file. Changes since v18: * Rewrite tests with the new design: execveat/AT_CHECK and securebits. * Simplify the capability dropping and improve it with the NOROOT securebits. * Replace most ASSERT with EXPECT. * Fix NULL execve's argv to avoid kernel warning. * Move tests to exec/ * Build a "false" static binary to test full execution path. Changes since v14: * Add Reviewed-by Kees Cook. Changes since v13: * Move -I to CFLAGS (suggested by Kees Cook). * Update sysctl name. Changes since v12: * Fix Makefile's license. Changes since v10: * Update selftest Makefile. Changes since v9: * Rename the syscall and the sysctl. * Update tests for enum trusted_for_usage Changes since v8: * Update with the dedicated syscall introspect_access(2) and the renamed fs.introspection_policy sysctl. * Remove check symlink which can't be use as is anymore. * Use socketpair(2) to test UNIX socket. Changes since v7: * Update tests with faccessat2/AT_INTERPRETED, including new ones to check that setting R_OK or W_OK returns EINVAL. * Add tests for memfd, pipefs and nsfs. * Rename and move back tests to a standalone directory. Changes since v6: * Add full combination tests for all file types, including block devices, character devices, fifos, sockets and symlinks. * Properly save and restore initial sysctl value for all tests. Changes since v5: * Refactor with FIXTURE_VARIANT, which make the tests much more easy to read and maintain. * Save and restore initial sysctl value (suggested by Kees Cook). * Test with a sysctl value of 0. * Check errno in sysctl_access_write test. * Update tests for the CAP_SYS_ADMIN switch. * Update tests to check -EISDIR (replacing -EACCES). * Replace FIXTURE_DATA() with FIXTURE() (spotted by Kees Cook). * Use global const strings. Changes since v3: * Replace RESOLVE_MAYEXEC with O_MAYEXEC. * Add tests to check that O_MAYEXEC is ignored by open(2) and openat(2). Changes since v2: * Move tests from exec/ to openat2/ . * Replace O_MAYEXEC with RESOLVE_MAYEXEC from openat2(2). * Cleanup tests. Changes since v1: * Move tests from yama/ to exec/ . * Fix _GNU_SOURCE in kselftest_harness.h . * Add a new test sysctl_access_write to check if CAP_MAC_ADMIN is taken into account. * Test directory execution which is always forbidden since commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files during execve()"), and also check that even the root user can not bypass file execution checks. * Make sure delete_workspace() always as enough right to succeed. * Cosmetic cleanup. --- tools/testing/selftests/exec/.gitignore | 2 + tools/testing/selftests/exec/Makefile | 7 + tools/testing/selftests/exec/check-exec.c | 456 ++++++++++++++++++++++ tools/testing/selftests/exec/config | 2 + tools/testing/selftests/exec/false.c | 5 + 5 files changed, 472 insertions(+) create mode 100644 tools/testing/selftests/exec/check-exec.c create mode 100644 tools/testing/selftests/exec/config create mode 100644 tools/testing/selftests/exec/false.c diff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore index a0dc5d4bf733..a32c63bb4df1 100644 --- a/tools/testing/selftests/exec/.gitignore +++ b/tools/testing/selftests/exec/.gitignore @@ -9,6 +9,8 @@ execveat.ephemeral execveat.denatured non-regular null-argv +/check-exec +/false /load_address.* !load_address.c /recursion-depth diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile index ba012bc5aab9..8713d1c862ae 100644 --- a/tools/testing/selftests/exec/Makefile +++ b/tools/testing/selftests/exec/Makefile @@ -1,6 +1,9 @@ # SPDX-License-Identifier: GPL-2.0 CFLAGS = -Wall CFLAGS += -Wno-nonnull +CFLAGS += $(KHDR_INCLUDES) + +LDLIBS += -lcap ALIGNS := 0x1000 0x200000 0x1000000 ALIGN_PIES := $(patsubst %,load_address.%,$(ALIGNS)) @@ -9,12 +12,14 @@ ALIGNMENT_TESTS := $(ALIGN_PIES) $(ALIGN_STATIC_PIES) TEST_PROGS := binfmt_script.py TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS) +TEST_GEN_PROGS_EXTENDED := false TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir # Makefile is a run-time dependency, since it's accessed by the execveat test TEST_FILES := Makefile TEST_GEN_PROGS += recursion-depth TEST_GEN_PROGS += null-argv +TEST_GEN_PROGS += check-exec EXTRA_CLEAN := $(OUTPUT)/subdir.moved $(OUTPUT)/execveat.moved $(OUTPUT)/xxxxx* \ $(OUTPUT)/S_I*.test @@ -38,3 +43,5 @@ $(OUTPUT)/load_address.0x%: load_address.c $(OUTPUT)/load_address.static.0x%: load_address.c $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \ -fPIE -static-pie $< -o $@ +$(OUTPUT)/false: false.c + $(CC) $(CFLAGS) $(LDFLAGS) -static $< -o $@ diff --git a/tools/testing/selftests/exec/check-exec.c b/tools/testing/selftests/exec/check-exec.c new file mode 100644 index 000000000000..4d3f4525e1e1 --- /dev/null +++ b/tools/testing/selftests/exec/check-exec.c @@ -0,0 +1,456 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Test execveat(2) with AT_EXECVE_CHECK, and prctl(2) with + * SECBIT_EXEC_RESTRICT_FILE, SECBIT_EXEC_DENY_INTERACTIVE, and their locked + * counterparts. + * + * Copyright © 2018-2020 ANSSI + * Copyright © 2024 Microsoft Corporation + * + * Author: Mickaël Salaün + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* Defines AT_EXECVE_CHECK without type conflicts. */ +#define _ASM_GENERIC_FCNTL_H +#include + +#include "../kselftest_harness.h" + +static void drop_privileges(struct __test_metadata *const _metadata) +{ + const unsigned int noroot = SECBIT_NOROOT | SECBIT_NOROOT_LOCKED; + cap_t cap_p; + + if ((cap_get_secbits() & noroot) != noroot) + EXPECT_EQ(0, cap_set_secbits(noroot)); + + cap_p = cap_get_proc(); + EXPECT_NE(NULL, cap_p); + EXPECT_NE(-1, cap_clear(cap_p)); + + /* + * Drops everything, especially CAP_SETPCAP, CAP_DAC_OVERRIDE, and + * CAP_DAC_READ_SEARCH. + */ + EXPECT_NE(-1, cap_set_proc(cap_p)); + EXPECT_NE(-1, cap_free(cap_p)); +} + +static int test_secbits_set(const unsigned int secbits) +{ + int err; + + err = prctl(PR_SET_SECUREBITS, secbits); + if (err) + return errno; + return 0; +} + +FIXTURE(access) +{ + int memfd, pipefd; + int pipe_fds[2], socket_fds[2]; +}; + +FIXTURE_VARIANT(access) +{ + const bool mount_exec; + const bool file_exec; +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(access, mount_exec_file_exec) { + /* clang-format on */ + .mount_exec = true, + .file_exec = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(access, mount_exec_file_noexec) { + /* clang-format on */ + .mount_exec = true, + .file_exec = false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(access, mount_noexec_file_exec) { + /* clang-format on */ + .mount_exec = false, + .file_exec = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(access, mount_noexec_file_noexec) { + /* clang-format on */ + .mount_exec = false, + .file_exec = false, +}; + +static const char binary_path[] = "./false"; +static const char workdir_path[] = "./test-mount"; +static const char reg_file_path[] = "./test-mount/regular_file"; +static const char dir_path[] = "./test-mount/directory"; +static const char block_dev_path[] = "./test-mount/block_device"; +static const char char_dev_path[] = "./test-mount/character_device"; +static const char fifo_path[] = "./test-mount/fifo"; + +FIXTURE_SETUP(access) +{ + int procfd_path_size; + static const char path_template[] = "/proc/self/fd/%d"; + char procfd_path[sizeof(path_template) + 10]; + + /* Makes sure we are not already restricted nor locked. */ + EXPECT_EQ(0, test_secbits_set(0)); + + /* + * Cleans previous workspace if any error previously happened (don't + * check errors). + */ + umount(workdir_path); + rmdir(workdir_path); + + /* Creates a clean mount point. */ + ASSERT_EQ(0, mkdir(workdir_path, 00700)); + ASSERT_EQ(0, mount("test", workdir_path, "tmpfs", + MS_MGC_VAL | (variant->mount_exec ? 0 : MS_NOEXEC), + "mode=0700,size=9m")); + + /* Creates a regular file. */ + ASSERT_EQ(0, mknod(reg_file_path, + S_IFREG | (variant->file_exec ? 0700 : 0600), 0)); + /* Creates a directory. */ + ASSERT_EQ(0, mkdir(dir_path, variant->file_exec ? 0700 : 0600)); + /* Creates a character device: /dev/null. */ + ASSERT_EQ(0, mknod(char_dev_path, S_IFCHR | 0400, makedev(1, 3))); + /* Creates a block device: /dev/loop0 */ + ASSERT_EQ(0, mknod(block_dev_path, S_IFBLK | 0400, makedev(7, 0))); + /* Creates a fifo. */ + ASSERT_EQ(0, mknod(fifo_path, S_IFIFO | 0600, 0)); + + /* Creates a regular file without user mount point. */ + self->memfd = memfd_create("test-exec-probe", MFD_CLOEXEC); + ASSERT_LE(0, self->memfd); + /* Sets mode, which must be ignored by the exec check. */ + ASSERT_EQ(0, fchmod(self->memfd, variant->file_exec ? 0700 : 0600)); + + /* Creates a pipefs file descriptor. */ + ASSERT_EQ(0, pipe(self->pipe_fds)); + procfd_path_size = snprintf(procfd_path, sizeof(procfd_path), + path_template, self->pipe_fds[0]); + ASSERT_LT(procfd_path_size, sizeof(procfd_path)); + self->pipefd = open(procfd_path, O_RDWR | O_CLOEXEC); + ASSERT_LE(0, self->pipefd); + ASSERT_EQ(0, fchmod(self->pipefd, variant->file_exec ? 0700 : 0600)); + + /* Creates a socket file descriptor. */ + ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0, + self->socket_fds)); +} + +FIXTURE_TEARDOWN_PARENT(access) +{ + /* There is no need to unlink the test files. */ + EXPECT_EQ(0, umount(workdir_path)); + EXPECT_EQ(0, rmdir(workdir_path)); +} + +static void fill_exec_fd(struct __test_metadata *_metadata, const int fd_out) +{ + char buf[1024]; + size_t len; + int fd_in; + + fd_in = open(binary_path, O_CLOEXEC | O_RDONLY); + ASSERT_LE(0, fd_in); + /* Cannot use copy_file_range(2) because of EXDEV. */ + len = read(fd_in, buf, sizeof(buf)); + EXPECT_LE(0, len); + while (len > 0) { + EXPECT_EQ(len, write(fd_out, buf, len)) + { + TH_LOG("Failed to write: %s (%d)", strerror(errno), + errno); + } + len = read(fd_in, buf, sizeof(buf)); + EXPECT_LE(0, len); + } + EXPECT_EQ(0, close(fd_in)); +} + +static void fill_exec_path(struct __test_metadata *_metadata, + const char *const path) +{ + int fd_out; + + fd_out = open(path, O_CLOEXEC | O_WRONLY); + ASSERT_LE(0, fd_out) + { + TH_LOG("Failed to open %s: %s", path, strerror(errno)); + } + fill_exec_fd(_metadata, fd_out); + EXPECT_EQ(0, close(fd_out)); +} + +static void test_exec_fd(struct __test_metadata *_metadata, const int fd, + const int err_code) +{ + char *const argv[] = { "", NULL }; + int access_ret, access_errno; + + /* + * If we really execute fd, filled with the "false" binary, the current + * thread will exits with an error, which will be interpreted by the + * test framework as an error. With AT_EXECVE_CHECK, we only check a + * potential successful execution. + */ + access_ret = + execveat(fd, "", argv, NULL, AT_EMPTY_PATH | AT_EXECVE_CHECK); + access_errno = errno; + if (err_code) { + EXPECT_EQ(-1, access_ret); + EXPECT_EQ(err_code, access_errno) + { + TH_LOG("Wrong error for execveat(2): %s (%d)", + strerror(access_errno), errno); + } + } else { + EXPECT_EQ(0, access_ret) + { + TH_LOG("Access denied: %s", strerror(access_errno)); + } + } +} + +static void test_exec_path(struct __test_metadata *_metadata, + const char *const path, const int err_code) +{ + int flags = O_CLOEXEC; + int fd; + + /* Do not block on pipes. */ + if (path == fifo_path) + flags |= O_NONBLOCK; + + fd = open(path, flags | O_RDONLY); + ASSERT_LE(0, fd) + { + TH_LOG("Failed to open %s: %s", path, strerror(errno)); + } + test_exec_fd(_metadata, fd, err_code); + EXPECT_EQ(0, close(fd)); +} + +/* Tests that we don't get ENOEXEC. */ +TEST_F(access, regular_file_empty) +{ + const int exec = variant->mount_exec && variant->file_exec; + + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); +} + +TEST_F(access, regular_file_elf) +{ + const int exec = variant->mount_exec && variant->file_exec; + + fill_exec_path(_metadata, reg_file_path); + + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); +} + +/* Tests that we don't get ENOEXEC. */ +TEST_F(access, memfd_empty) +{ + const int exec = variant->file_exec; + + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); +} + +TEST_F(access, memfd_elf) +{ + const int exec = variant->file_exec; + + fill_exec_fd(_metadata, self->memfd); + + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); +} + +TEST_F(access, non_regular_files) +{ + test_exec_path(_metadata, dir_path, EACCES); + test_exec_path(_metadata, block_dev_path, EACCES); + test_exec_path(_metadata, char_dev_path, EACCES); + test_exec_path(_metadata, fifo_path, EACCES); + test_exec_fd(_metadata, self->socket_fds[0], EACCES); + test_exec_fd(_metadata, self->pipefd, EACCES); +} + +/* clang-format off */ +FIXTURE(secbits) {}; +/* clang-format on */ + +FIXTURE_VARIANT(secbits) +{ + const bool is_privileged; + const int error; +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(secbits, priv) { + /* clang-format on */ + .is_privileged = true, + .error = 0, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(secbits, unpriv) { + /* clang-format on */ + .is_privileged = false, + .error = EPERM, +}; + +FIXTURE_SETUP(secbits) +{ + /* Makes sure no exec bits are set. */ + EXPECT_EQ(0, test_secbits_set(0)); + EXPECT_EQ(0, prctl(PR_GET_SECUREBITS)); + + if (!variant->is_privileged) + drop_privileges(_metadata); +} + +FIXTURE_TEARDOWN(secbits) +{ +} + +TEST_F(secbits, legacy) +{ + EXPECT_EQ(variant->error, test_secbits_set(0)); +} + +#define CHILD(...) \ + do { \ + pid_t child = vfork(); \ + EXPECT_LE(0, child); \ + if (child == 0) { \ + __VA_ARGS__; \ + _exit(0); \ + } \ + } while (0) + +TEST_F(secbits, exec) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_EXEC_RESTRICT_FILE; + EXPECT_EQ(0, test_secbits_set(secbits)); + EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS)); + CHILD(EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS))); + + secbits |= SECBIT_EXEC_DENY_INTERACTIVE; + EXPECT_EQ(0, test_secbits_set(secbits)); + EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS)); + CHILD(EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS))); + + secbits &= ~(SECBIT_EXEC_RESTRICT_FILE | SECBIT_EXEC_DENY_INTERACTIVE); + EXPECT_EQ(0, test_secbits_set(secbits)); + EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS)); + CHILD(EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS))); +} + +TEST_F(secbits, check_locked_set) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_EXEC_RESTRICT_FILE; + EXPECT_EQ(0, test_secbits_set(secbits)); + secbits |= SECBIT_EXEC_RESTRICT_FILE_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock set but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_EXEC_RESTRICT_FILE; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +TEST_F(secbits, check_locked_unset) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_EXEC_RESTRICT_FILE_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock unset but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_EXEC_RESTRICT_FILE; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +TEST_F(secbits, restrict_locked_set) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_EXEC_DENY_INTERACTIVE; + EXPECT_EQ(0, test_secbits_set(secbits)); + secbits |= SECBIT_EXEC_DENY_INTERACTIVE_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock set but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_EXEC_DENY_INTERACTIVE; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +TEST_F(secbits, restrict_locked_unset) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_EXEC_DENY_INTERACTIVE_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock unset but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_EXEC_DENY_INTERACTIVE; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/exec/config b/tools/testing/selftests/exec/config new file mode 100644 index 000000000000..c308079867b3 --- /dev/null +++ b/tools/testing/selftests/exec/config @@ -0,0 +1,2 @@ +CONFIG_BLK_DEV=y +CONFIG_BLK_DEV_LOOP=y diff --git a/tools/testing/selftests/exec/false.c b/tools/testing/selftests/exec/false.c new file mode 100644 index 000000000000..104383ec3a79 --- /dev/null +++ b/tools/testing/selftests/exec/false.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0 +int main(void) +{ + return 1; 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Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, =?utf-8?q?G=C3=BCnther_Noack?= Subject: [PATCH v22 4/8] selftests/landlock: Add tests for execveat + AT_EXECVE_CHECK Date: Thu, 5 Dec 2024 17:09:21 +0100 Message-ID: <20241205160925.230119-5-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha Extend layout1.execute with the new AT_EXECVE_CHECK flag. The semantic with AT_EXECVE_CHECK is the same as with a simple execve(2), LANDLOCK_ACCESS_FS_EXECUTE is enforced the same way. Cc: Günther Noack Cc: Kees Cook Cc: Paul Moore Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-5-mic@digikod.net --- Changes since v20: * Rename AT_CHECK to AT_EXECVE_CHECK. --- tools/testing/selftests/landlock/fs_test.c | 27 ++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c index 6788762188fe..cd66901be612 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -37,6 +37,10 @@ #include #include +/* Defines AT_EXECVE_CHECK without type conflicts. */ +#define _ASM_GENERIC_FCNTL_H +#include + #include "common.h" #ifndef renameat2 @@ -2008,6 +2012,22 @@ static void test_execute(struct __test_metadata *const _metadata, const int err, }; } +static void test_check_exec(struct __test_metadata *const _metadata, + const int err, const char *const path) +{ + int ret; + char *const argv[] = { (char *)path, NULL }; + + ret = execveat(AT_FDCWD, path, argv, NULL, + AT_EMPTY_PATH | AT_EXECVE_CHECK); + if (err) { + EXPECT_EQ(-1, ret); + EXPECT_EQ(errno, err); + } else { + EXPECT_EQ(0, ret); + } +} + TEST_F_FORK(layout1, execute) { const struct rule rules[] = { @@ -2025,20 +2045,27 @@ TEST_F_FORK(layout1, execute) copy_binary(_metadata, file1_s1d2); copy_binary(_metadata, file1_s1d3); + /* Checks before file1_s1d1 being denied. */ + test_execute(_metadata, 0, file1_s1d1); + test_check_exec(_metadata, 0, file1_s1d1); + enforce_ruleset(_metadata, ruleset_fd); ASSERT_EQ(0, close(ruleset_fd)); ASSERT_EQ(0, test_open(dir_s1d1, O_RDONLY)); ASSERT_EQ(0, test_open(file1_s1d1, O_RDONLY)); test_execute(_metadata, EACCES, file1_s1d1); + test_check_exec(_metadata, EACCES, file1_s1d1); ASSERT_EQ(0, test_open(dir_s1d2, O_RDONLY)); ASSERT_EQ(0, test_open(file1_s1d2, O_RDONLY)); test_execute(_metadata, 0, file1_s1d2); + test_check_exec(_metadata, 0, file1_s1d2); ASSERT_EQ(0, test_open(dir_s1d3, O_RDONLY)); ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY)); test_execute(_metadata, 0, file1_s1d3); + test_check_exec(_metadata, 0, file1_s1d3); } TEST_F_FORK(layout1, link) From patchwork Thu Dec 5 16:09:22 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 13895698 Received: from smtp-bc0c.mail.infomaniak.ch (smtp-bc0c.mail.infomaniak.ch [45.157.188.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0A626225790; Thu, 5 Dec 2024 16:10:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.157.188.12 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733415007; cv=none; b=SYhnHdNCaD7qUJFHT+La8nrTt9lvQ4fUR+HaxXUSLgUqumPrSE1lQJD/C94DVcvuHYX7yJ9nhtjry6I6guy+qWonPwgUQpPJLCG70fwR6s1ScPdhrRksDKPMzPzSWC8EEieFLpXiZ/CFX0PzzzbafV2OWrkHf1mPJ5rkX98lpXs= ARC-Message-Signature: i=1; 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Thu, 5 Dec 2024 17:09:55 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1733414995; bh=qnmDxHFXi6N4fToRcmhVEwvrvRtsDGj6kxHcV7qI41w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=whclG3JSDD/Ew1OxL9RBYs5MGeSCn4prrQwcJ0jIyZRBfUSfy4hYsrAvSO6A6NsqI hq/rpFUs1xIw8SJXqDSvfYrRnTBpuOlgRpt4uHhrjzjDIKWGBKNRUVnumINBWJMmkO QJhN+SpANCYo0Zk4oiPqSQLxpxfXXSJcju023kYM= Received: from unknown by smtp-3-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 4Y3zqj4m75zgmB; Thu, 5 Dec 2024 17:09:53 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Al Viro , Christian Brauner , Kees Cook , Paul Moore , Serge Hallyn Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Adhemerval Zanella Netto , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Elliott Hughes , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Linus Torvalds , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH v22 5/8] samples/check-exec: Add set-exec Date: Thu, 5 Dec 2024 17:09:22 +0100 Message-ID: <20241205160925.230119-6-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha Add a simple tool to set SECBIT_EXEC_RESTRICT_FILE or SECBIT_EXEC_DENY_INTERACTIVE before executing a command. This is useful to easily test against enlighten script interpreters. Cc: Al Viro Cc: Christian Brauner Cc: Kees Cook Cc: Paul Moore Cc: Serge Hallyn Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-6-mic@digikod.net --- Changes since v19: * Rename file and directory. * Update securebits and related arguments. * Remove useless call to prctl() when securebits are unchanged. --- samples/Kconfig | 7 +++ samples/Makefile | 1 + samples/check-exec/.gitignore | 1 + samples/check-exec/Makefile | 14 ++++++ samples/check-exec/set-exec.c | 85 +++++++++++++++++++++++++++++++++++ 5 files changed, 108 insertions(+) create mode 100644 samples/check-exec/.gitignore create mode 100644 samples/check-exec/Makefile create mode 100644 samples/check-exec/set-exec.c diff --git a/samples/Kconfig b/samples/Kconfig index b288d9991d27..efa28ceadc42 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -291,6 +291,13 @@ config SAMPLE_CGROUP help Build samples that demonstrate the usage of the cgroup API. +config SAMPLE_CHECK_EXEC + bool "Exec secure bits examples" + depends on CC_CAN_LINK && HEADERS_INSTALL + help + Build a tool to easily configure SECBIT_EXEC_RESTRICT_FILE and + SECBIT_EXEC_DENY_INTERACTIVE. + source "samples/rust/Kconfig" endif # SAMPLES diff --git a/samples/Makefile b/samples/Makefile index b85fa64390c5..f988202f3a30 100644 --- a/samples/Makefile +++ b/samples/Makefile @@ -3,6 +3,7 @@ subdir-$(CONFIG_SAMPLE_AUXDISPLAY) += auxdisplay subdir-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs +subdir-$(CONFIG_SAMPLE_CHECK_EXEC) += check-exec subdir-$(CONFIG_SAMPLE_CGROUP) += cgroup obj-$(CONFIG_SAMPLE_CONFIGFS) += configfs/ obj-$(CONFIG_SAMPLE_CONNECTOR) += connector/ diff --git a/samples/check-exec/.gitignore b/samples/check-exec/.gitignore new file mode 100644 index 000000000000..3f8119112ccf --- /dev/null +++ b/samples/check-exec/.gitignore @@ -0,0 +1 @@ +/set-exec diff --git a/samples/check-exec/Makefile b/samples/check-exec/Makefile new file mode 100644 index 000000000000..d9f976e3ff98 --- /dev/null +++ b/samples/check-exec/Makefile @@ -0,0 +1,14 @@ +# SPDX-License-Identifier: BSD-3-Clause + +userprogs-always-y := \ + set-exec + +userccflags += -I usr/include + +.PHONY: all clean + +all: + $(MAKE) -C ../.. samples/check-exec/ + +clean: + $(MAKE) -C ../.. M=samples/check-exec/ clean diff --git a/samples/check-exec/set-exec.c b/samples/check-exec/set-exec.c new file mode 100644 index 000000000000..ba86a60a20dd --- /dev/null +++ b/samples/check-exec/set-exec.c @@ -0,0 +1,85 @@ +// SPDX-License-Identifier: BSD-3-Clause +/* + * Simple tool to set SECBIT_EXEC_RESTRICT_FILE, SECBIT_EXEC_DENY_INTERACTIVE, + * before executing a command. + * + * Copyright © 2024 Microsoft Corporation + */ + +#define _GNU_SOURCE +#define __SANE_USERSPACE_TYPES__ +#include +#include +#include +#include +#include +#include +#include +#include +#include + +static void print_usage(const char *argv0) +{ + fprintf(stderr, "usage: %s -f|-i -- [args]...\n\n", argv0); + fprintf(stderr, "Execute a command with\n"); + fprintf(stderr, "- SECBIT_EXEC_RESTRICT_FILE set: -f\n"); + fprintf(stderr, "- SECBIT_EXEC_DENY_INTERACTIVE set: -i\n"); +} + +int main(const int argc, char *const argv[], char *const *const envp) +{ + const char *cmd_path; + char *const *cmd_argv; + int opt, secbits_cur, secbits_new; + bool has_policy = false; + + secbits_cur = prctl(PR_GET_SECUREBITS); + if (secbits_cur == -1) { + /* + * This should never happen, except with a buggy seccomp + * filter. + */ + perror("ERROR: Failed to get securebits"); + return 1; + } + + secbits_new = secbits_cur; + while ((opt = getopt(argc, argv, "fi")) != -1) { + switch (opt) { + case 'f': + secbits_new |= SECBIT_EXEC_RESTRICT_FILE | + SECBIT_EXEC_RESTRICT_FILE_LOCKED; + has_policy = true; + break; + case 'i': + secbits_new |= SECBIT_EXEC_DENY_INTERACTIVE | + SECBIT_EXEC_DENY_INTERACTIVE_LOCKED; + has_policy = true; + break; + default: + print_usage(argv[0]); + return 1; + } + } + + if (!argv[optind] || !has_policy) { + print_usage(argv[0]); + return 1; + } + + if (secbits_cur != secbits_new && + prctl(PR_SET_SECUREBITS, secbits_new)) { + perror("Failed to set secure bit(s)."); + fprintf(stderr, + "Hint: The running kernel may not support this feature.\n"); + return 1; + } + + cmd_path = argv[optind]; + cmd_argv = argv + optind; + fprintf(stderr, "Executing command...\n"); + execvpe(cmd_path, cmd_argv, envp); + fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path, + strerror(errno)); + return 1; +} From patchwork Thu Dec 5 16:09:23 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 13895695 Received: from smtp-190b.mail.infomaniak.ch (smtp-190b.mail.infomaniak.ch [185.125.25.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4CF9B221452 for ; Thu, 5 Dec 2024 16:09:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.125.25.11 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733415001; cv=none; b=mo3EiaAyZHOmGTsIPyoqBavqmASzFuXt0GnPW3kxEvDltRQMnrHnjir2AxJp16VOnEljgvfoXoaLd5qzGvxkDkjqzjtHxzBp86ymS9OhS2GQTxsUqsrkfjfg9cQGnq1tLamxfb0lqffkbOysgnLLJZuTjksxcCIt32P7WWWUVFs= ARC-Message-Signature: i=1; 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Thu, 5 Dec 2024 17:09:57 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1733414997; bh=eagq1eHZLSX+a8YTmNs769Rc9572rghldm9U8dLwCRw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cgoZb4ikCgvdxtvFokaW437+RCeYwdWHNNIu5Od+bp/6eJ7w1Gc3r9n5ugZ+7D7l9 xhvm5qIGig5Ir+mRcLC6FVyxtcSKZeFm6FdIRc7P5rq1lCSQxK1oIpXEaXSzmwyxox f0T2YSctMvA8B0Vm/9Ur53y0DH923Wykydb5nr6M= Received: from unknown by smtp-4-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4Y3zqm0gYfzfsG; Thu, 5 Dec 2024 17:09:56 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Al Viro , Christian Brauner , Kees Cook , Paul Moore , Serge Hallyn Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Adhemerval Zanella Netto , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Elliott Hughes , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Linus Torvalds , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Kees Cook , =?utf-8?b?TsOtY29sYXMgRi4gUi4gQS4gUHJhZG8=?= Subject: [PATCH v22 6/8] selftests: ktap_helpers: Fix uninitialized variable Date: Thu, 5 Dec 2024 17:09:23 +0100 Message-ID: <20241205160925.230119-7-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha __ktap_test() may be called without the optional third argument which is an issue for scripts using `set -u` to detect uninitialized variables and potential bugs. Fix this optional "directive" argument by either using the third argument or an empty string. This is required for the next commit to properly test script execution control. Cc: Kees Cook Cc: Nícolas F. R. A. Prado Cc: Shuah Khan Fixes: 14571ab1ad21 ("kselftest: Add new test for detecting unprobed Devicetree devices") Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-7-mic@digikod.net --- Also sent as a standalone patch: https://lore.kernel.org/r/20241127160342.31472-1-mic@digikod.net --- tools/testing/selftests/kselftest/ktap_helpers.sh | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/testing/selftests/kselftest/ktap_helpers.sh b/tools/testing/selftests/kselftest/ktap_helpers.sh index 79a125eb24c2..14e7f3ec3f84 100644 --- a/tools/testing/selftests/kselftest/ktap_helpers.sh +++ b/tools/testing/selftests/kselftest/ktap_helpers.sh @@ -40,7 +40,7 @@ ktap_skip_all() { __ktap_test() { result="$1" description="$2" - directive="$3" # optional + directive="${3:-}" # optional local directive_str= [ ! -z "$directive" ] && directive_str="# $directive" From patchwork Thu Dec 5 16:09:24 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 13895696 Received: from smtp-8fa8.mail.infomaniak.ch (smtp-8fa8.mail.infomaniak.ch [83.166.143.168]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 13E6B22576F for ; Thu, 5 Dec 2024 16:10:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=83.166.143.168 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733415005; cv=none; b=AB2wEWtxpmRdQAzKxVWGOZN1duvIz25z1isMmSt3VhOuGS+7kuBXhMkb41xZUp+3lwjD2utt5iWB1l4kIwwl4WUka8Ez4sHiXMIkvGQAQtFmD+kdvWMP9dshJoqZ3ss0lCi+Rbo7GX4TvJ6Ju3M8eXZ0KzibckfVqTp+FNRRrT0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733415005; c=relaxed/simple; bh=VRYvgDyDVtZIu+TZwh4g2ki+ASM5TFMoJizda4Hql5Y=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=h2ar7CqQEZVGRNse0A9HRuyA50+tzV9Snzi52Jc+Ow2kCmMP+YGO4z6H1BsdsJFVoqIObMAz3A5ztLk+bTjZS5noLSIfOWa3D8PnL/XsuCCItSRnuyukc9WpuJhZLvcAqn+nEcQZfyWtRiqH2Or+sG88jRUnuBxjcALUHhh+naU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net; spf=pass smtp.mailfrom=digikod.net; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b=Fh179Kzl; arc=none smtp.client-ip=83.166.143.168 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=digikod.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b="Fh179Kzl" Received: from smtp-3-0000.mail.infomaniak.ch (unknown [IPv6:2001:1600:4:17::246b]) by smtp-3-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4Y3zqp6fGBz6xC; Thu, 5 Dec 2024 17:09:58 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1733414998; bh=wN6VlP4B4VGpj//j5wE9qGWAOoLrlB6aREyPO378avI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Fh179KzllB9jmycjPCRxXqoSWeTV5C2qXWgXlA501R8DeD6IL2v8ZRq0JpmBUGSzN EKYt0fAnYhYbM3yWOoD+f7sBdtwOcd6G6MyDnkp9FLHji4OJUp13LqT9r21xIChmQP m9t6Y8cpd+TcRaF4+pCbGlg9ItNkDDq9iDj5g4s0= Received: from unknown by smtp-3-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 4Y3zqn5HJKzgWc; Thu, 5 Dec 2024 17:09:57 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Al Viro , Christian Brauner , Kees Cook , Paul Moore , Serge Hallyn Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Adhemerval Zanella Netto , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Elliott Hughes , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Linus Torvalds , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH v22 7/8] samples/check-exec: Add an enlighten "inc" interpreter and 28 tests Date: Thu, 5 Dec 2024 17:09:24 +0100 Message-ID: <20241205160925.230119-8-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha Add a very simple script interpreter called "inc" that can evaluate two different commands (one per line): - "?" to initialize a counter from user's input; - "+" to increment the counter (which is set to 0 by default). It is enlighten to only interpret executable files according to AT_EXECVE_CHECK and the related securebits: # Executing a script with RESTRICT_FILE is only allowed if the script # is executable: ./set-exec -f -- ./inc script-exec.inc # Allowed ./set-exec -f -- ./inc script-noexec.inc # Denied # Executing stdin with DENY_INTERACTIVE is only allowed if stdin is an # executable regular file: ./set-exec -i -- ./inc -i < script-exec.inc # Allowed ./set-exec -i -- ./inc -i < script-noexec.inc # Denied # However, a pipe is not executable and it is then denied: cat script-noexec.inc | ./set-exec -i -- ./inc -i # Denied # Executing raw data (e.g. command argument) with DENY_INTERACTIVE is # always denied. ./set-exec -i -- ./inc -c "+" # Denied ./inc -c "$( Cc: Christian Brauner Cc: Kees Cook Cc: Paul Moore Cc: Serge Hallyn Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-8-mic@digikod.net --- Changes since v21: * Move the ktap_helpers.sh fix to a standalone previous commit (that should be backported). * Add missing SPDX-License-Identifier headers to test scripts. Changes since v20: * Rename AT_CHECK to AT_EXECVE_CHECK. Changes since v19: * New patch. --- samples/Kconfig | 4 +- samples/check-exec/.gitignore | 1 + samples/check-exec/Makefile | 1 + samples/check-exec/inc.c | 205 ++++++++++++++++++ samples/check-exec/run-script-ask.inc | 9 + samples/check-exec/script-ask.inc | 5 + samples/check-exec/script-exec.inc | 4 + samples/check-exec/script-noexec.inc | 4 + tools/testing/selftests/exec/.gitignore | 2 + tools/testing/selftests/exec/Makefile | 14 +- .../selftests/exec/check-exec-tests.sh | 205 ++++++++++++++++++ 11 files changed, 451 insertions(+), 3 deletions(-) create mode 100644 samples/check-exec/inc.c create mode 100755 samples/check-exec/run-script-ask.inc create mode 100755 samples/check-exec/script-ask.inc create mode 100755 samples/check-exec/script-exec.inc create mode 100644 samples/check-exec/script-noexec.inc create mode 100755 tools/testing/selftests/exec/check-exec-tests.sh diff --git a/samples/Kconfig b/samples/Kconfig index efa28ceadc42..84a9d4e8d947 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -296,7 +296,9 @@ config SAMPLE_CHECK_EXEC depends on CC_CAN_LINK && HEADERS_INSTALL help Build a tool to easily configure SECBIT_EXEC_RESTRICT_FILE and - SECBIT_EXEC_DENY_INTERACTIVE. + SECBIT_EXEC_DENY_INTERACTIVE, and a simple script interpreter to + demonstrate how they should be used with execveat(2) + + AT_EXECVE_CHECK. source "samples/rust/Kconfig" diff --git a/samples/check-exec/.gitignore b/samples/check-exec/.gitignore index 3f8119112ccf..cd759a19dacd 100644 --- a/samples/check-exec/.gitignore +++ b/samples/check-exec/.gitignore @@ -1 +1,2 @@ +/inc /set-exec diff --git a/samples/check-exec/Makefile b/samples/check-exec/Makefile index d9f976e3ff98..c4f08ad0f8e3 100644 --- a/samples/check-exec/Makefile +++ b/samples/check-exec/Makefile @@ -1,6 +1,7 @@ # SPDX-License-Identifier: BSD-3-Clause userprogs-always-y := \ + inc \ set-exec userccflags += -I usr/include diff --git a/samples/check-exec/inc.c b/samples/check-exec/inc.c new file mode 100644 index 000000000000..94b87569d2a2 --- /dev/null +++ b/samples/check-exec/inc.c @@ -0,0 +1,205 @@ +// SPDX-License-Identifier: BSD-3-Clause +/* + * Very simple script interpreter that can evaluate two different commands (one + * per line): + * - "?" to initialize a counter from user's input; + * - "+" to increment the counter (which is set to 0 by default). + * + * See tools/testing/selftests/exec/check-exec-tests.sh and + * Documentation/userspace-api/check_exec.rst + * + * Copyright © 2024 Microsoft Corporation + */ + +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* Returns 1 on error, 0 otherwise. */ +static int interpret_buffer(char *buffer, size_t buffer_size) +{ + char *line, *saveptr = NULL; + long long number = 0; + + /* Each command is the first character of a line. */ + saveptr = NULL; + line = strtok_r(buffer, "\n", &saveptr); + while (line) { + if (*line != '#' && strlen(line) != 1) { + fprintf(stderr, "# ERROR: Unknown string\n"); + return 1; + } + switch (*line) { + case '#': + /* Skips shebang and comments. */ + break; + case '+': + /* Increments and prints the number. */ + number++; + printf("%lld\n", number); + break; + case '?': + /* Reads integer from stdin. */ + fprintf(stderr, "> Enter new number: \n"); + if (scanf("%lld", &number) != 1) { + fprintf(stderr, + "# WARNING: Failed to read number from stdin\n"); + } + break; + default: + fprintf(stderr, "# ERROR: Unknown character '%c'\n", + *line); + return 1; + } + line = strtok_r(NULL, "\n", &saveptr); + } + return 0; +} + +/* Returns 1 on error, 0 otherwise. */ +static int interpret_stream(FILE *script, char *const script_name, + char *const *const envp, const bool restrict_stream) +{ + int err; + char *const script_argv[] = { script_name, NULL }; + char buf[128] = {}; + size_t buf_size = sizeof(buf); + + /* + * We pass a valid argv and envp to the kernel to emulate a native + * script execution. We must use the script file descriptor instead of + * the script path name to avoid race conditions. + */ + err = execveat(fileno(script), "", script_argv, envp, + AT_EMPTY_PATH | AT_EXECVE_CHECK); + if (err && restrict_stream) { + perror("ERROR: Script execution check"); + return 1; + } + + /* Reads script. */ + buf_size = fread(buf, 1, buf_size - 1, script); + return interpret_buffer(buf, buf_size); +} + +static void print_usage(const char *argv0) +{ + fprintf(stderr, "usage: %s | -i | -c \n\n", + argv0); + fprintf(stderr, "Example:\n"); + fprintf(stderr, " ./set-exec -fi -- ./inc -i < script-exec.inc\n"); +} + +int main(const int argc, char *const argv[], char *const *const envp) +{ + int opt; + char *cmd = NULL; + char *script_name = NULL; + bool interpret_stdin = false; + FILE *script_file = NULL; + int secbits; + bool deny_interactive, restrict_file; + size_t arg_nb; + + secbits = prctl(PR_GET_SECUREBITS); + if (secbits == -1) { + /* + * This should never happen, except with a buggy seccomp + * filter. + */ + perror("ERROR: Failed to get securebits"); + return 1; + } + + deny_interactive = !!(secbits & SECBIT_EXEC_DENY_INTERACTIVE); + restrict_file = !!(secbits & SECBIT_EXEC_RESTRICT_FILE); + + while ((opt = getopt(argc, argv, "c:i")) != -1) { + switch (opt) { + case 'c': + if (cmd) { + fprintf(stderr, "ERROR: Command already set"); + return 1; + } + cmd = optarg; + break; + case 'i': + interpret_stdin = true; + break; + default: + print_usage(argv[0]); + return 1; + } + } + + /* Checks that only one argument is used, or read stdin. */ + arg_nb = !!cmd + !!interpret_stdin; + if (arg_nb == 0 && argc == 2) { + script_name = argv[1]; + } else if (arg_nb != 1) { + print_usage(argv[0]); + return 1; + } + + if (cmd) { + /* + * Other kind of interactive interpretations should be denied + * as well (e.g. CLI arguments passing script snippets, + * environment variables interpreted as script). However, any + * way to pass script files should only be restricted according + * to restrict_file. + */ + if (deny_interactive) { + fprintf(stderr, + "ERROR: Interactive interpretation denied.\n"); + return 1; + } + + return interpret_buffer(cmd, strlen(cmd)); + } + + if (interpret_stdin && !script_name) { + script_file = stdin; + /* + * As for any execve(2) call, this path may be logged by the + * kernel. + */ + script_name = "/proc/self/fd/0"; + /* + * When stdin is used, it can point to a regular file or a + * pipe. Restrict stdin execution according to + * SECBIT_EXEC_DENY_INTERACTIVE but always allow executable + * files (which are not considered as interactive inputs). + */ + return interpret_stream(script_file, script_name, envp, + deny_interactive); + } else if (script_name && !interpret_stdin) { + /* + * In this sample, we don't pass any argument to scripts, but + * otherwise we would have to forge an argv with such + * arguments. + */ + script_file = fopen(script_name, "r"); + if (!script_file) { + perror("ERROR: Failed to open script"); + return 1; + } + /* + * Restricts file execution according to + * SECBIT_EXEC_RESTRICT_FILE. + */ + return interpret_stream(script_file, script_name, envp, + restrict_file); + } + + print_usage(argv[0]); + return 1; +} diff --git a/samples/check-exec/run-script-ask.inc b/samples/check-exec/run-script-ask.inc new file mode 100755 index 000000000000..8ef0fdc37266 --- /dev/null +++ b/samples/check-exec/run-script-ask.inc @@ -0,0 +1,9 @@ +#!/usr/bin/env sh +# SPDX-License-Identifier: BSD-3-Clause + +DIR="$(dirname -- "$0")" + +PATH="${PATH}:${DIR}" + +set -x +"${DIR}/script-ask.inc" diff --git a/samples/check-exec/script-ask.inc b/samples/check-exec/script-ask.inc new file mode 100755 index 000000000000..720a8e649225 --- /dev/null +++ b/samples/check-exec/script-ask.inc @@ -0,0 +1,5 @@ +#!/usr/bin/env inc +# SPDX-License-Identifier: BSD-3-Clause + +? ++ diff --git a/samples/check-exec/script-exec.inc b/samples/check-exec/script-exec.inc new file mode 100755 index 000000000000..3245cb9d8dd1 --- /dev/null +++ b/samples/check-exec/script-exec.inc @@ -0,0 +1,4 @@ +#!/usr/bin/env inc +# SPDX-License-Identifier: BSD-3-Clause + ++ diff --git a/samples/check-exec/script-noexec.inc b/samples/check-exec/script-noexec.inc new file mode 100644 index 000000000000..3245cb9d8dd1 --- /dev/null +++ b/samples/check-exec/script-noexec.inc @@ -0,0 +1,4 @@ +#!/usr/bin/env inc +# SPDX-License-Identifier: BSD-3-Clause + ++ diff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore index a32c63bb4df1..7f3d1ae762ec 100644 --- a/tools/testing/selftests/exec/.gitignore +++ b/tools/testing/selftests/exec/.gitignore @@ -11,9 +11,11 @@ non-regular null-argv /check-exec /false +/inc /load_address.* !load_address.c /recursion-depth +/set-exec xxxxxxxx* pipe S_I*.test diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile index 8713d1c862ae..45a3cfc435cf 100644 --- a/tools/testing/selftests/exec/Makefile +++ b/tools/testing/selftests/exec/Makefile @@ -10,9 +10,9 @@ ALIGN_PIES := $(patsubst %,load_address.%,$(ALIGNS)) ALIGN_STATIC_PIES := $(patsubst %,load_address.static.%,$(ALIGNS)) ALIGNMENT_TESTS := $(ALIGN_PIES) $(ALIGN_STATIC_PIES) -TEST_PROGS := binfmt_script.py +TEST_PROGS := binfmt_script.py check-exec-tests.sh TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS) -TEST_GEN_PROGS_EXTENDED := false +TEST_GEN_PROGS_EXTENDED := false inc set-exec script-exec.inc script-noexec.inc TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir # Makefile is a run-time dependency, since it's accessed by the execveat test TEST_FILES := Makefile @@ -26,6 +26,8 @@ EXTRA_CLEAN := $(OUTPUT)/subdir.moved $(OUTPUT)/execveat.moved $(OUTPUT)/xxxxx* include ../lib.mk +CHECK_EXEC_SAMPLES := $(top_srcdir)/samples/check-exec + $(OUTPUT)/subdir: mkdir -p $@ $(OUTPUT)/script: Makefile @@ -45,3 +47,11 @@ $(OUTPUT)/load_address.static.0x%: load_address.c -fPIE -static-pie $< -o $@ $(OUTPUT)/false: false.c $(CC) $(CFLAGS) $(LDFLAGS) -static $< -o $@ +$(OUTPUT)/inc: $(CHECK_EXEC_SAMPLES)/inc.c + $(CC) $(CFLAGS) $(LDFLAGS) $< -o $@ +$(OUTPUT)/set-exec: $(CHECK_EXEC_SAMPLES)/set-exec.c + $(CC) $(CFLAGS) $(LDFLAGS) $< -o $@ +$(OUTPUT)/script-exec.inc: $(CHECK_EXEC_SAMPLES)/script-exec.inc + cp $< $@ +$(OUTPUT)/script-noexec.inc: $(CHECK_EXEC_SAMPLES)/script-noexec.inc + cp $< $@ diff --git a/tools/testing/selftests/exec/check-exec-tests.sh b/tools/testing/selftests/exec/check-exec-tests.sh new file mode 100755 index 000000000000..87102906ae3c --- /dev/null +++ b/tools/testing/selftests/exec/check-exec-tests.sh @@ -0,0 +1,205 @@ +#!/usr/bin/env bash +# SPDX-License-Identifier: GPL-2.0 +# +# Test the "inc" interpreter. +# +# See include/uapi/linux/securebits.h, include/uapi/linux/fcntl.h and +# samples/check-exec/inc.c +# +# Copyright © 2024 Microsoft Corporation + +set -u -e -o pipefail + +EXPECTED_OUTPUT="1" +exec 2>/dev/null + +DIR="$(dirname $(readlink -f "$0"))" +source "${DIR}"/../kselftest/ktap_helpers.sh + +exec_direct() { + local expect="$1" + local script="$2" + shift 2 + local ret=0 + local out + + # Updates PATH for `env` to execute the `inc` interpreter. + out="$(PATH="." "$@" "${script}")" || ret=$? + + if [[ ${ret} -ne ${expect} ]]; then + echo "ERROR: Wrong expectation for direct file execution: ${ret}" + return 1 + fi + if [[ ${ret} -eq 0 && "${out}" != "${EXPECTED_OUTPUT}" ]]; then + echo "ERROR: Wrong output for direct file execution: ${out}" + return 1 + fi +} + +exec_indirect() { + local expect="$1" + local script="$2" + shift 2 + local ret=0 + local out + + # Script passed as argument. + out="$("$@" ./inc "${script}")" || ret=$? + + if [[ ${ret} -ne ${expect} ]]; then + echo "ERROR: Wrong expectation for indirect file execution: ${ret}" + return 1 + fi + if [[ ${ret} -eq 0 && "${out}" != "${EXPECTED_OUTPUT}" ]]; then + echo "ERROR: Wrong output for indirect file execution: ${out}" + return 1 + fi +} + +exec_stdin_reg() { + local expect="$1" + local script="$2" + shift 2 + local ret=0 + local out + + # Executing stdin must be allowed if the related file is executable. + out="$("$@" ./inc -i < "${script}")" || ret=$? + + if [[ ${ret} -ne ${expect} ]]; then + echo "ERROR: Wrong expectation for stdin regular file execution: ${ret}" + return 1 + fi + if [[ ${ret} -eq 0 && "${out}" != "${EXPECTED_OUTPUT}" ]]; then + echo "ERROR: Wrong output for stdin regular file execution: ${out}" + return 1 + fi +} + +exec_stdin_pipe() { + local expect="$1" + shift + local ret=0 + local out + + # A pipe is not executable. + out="$(cat script-exec.inc | "$@" ./inc -i)" || ret=$? + + if [[ ${ret} -ne ${expect} ]]; then + echo "ERROR: Wrong expectation for stdin pipe execution: ${ret}" + return 1 + fi +} + +exec_argument() { + local expect="$1" + local ret=0 + shift + local out + + # Script not coming from a file must not be executed. + out="$("$@" ./inc -c "$(< script-exec.inc)")" || ret=$? + + if [[ ${ret} -ne ${expect} ]]; then + echo "ERROR: Wrong expectation for arbitrary argument execution: ${ret}" + return 1 + fi + if [[ ${ret} -eq 0 && "${out}" != "${EXPECTED_OUTPUT}" ]]; then + echo "ERROR: Wrong output for arbitrary argument execution: ${out}" + return 1 + fi +} + +exec_interactive() { + exec_stdin_pipe "$@" + exec_argument "$@" +} + +ktap_test() { + ktap_test_result "$*" "$@" +} + +ktap_print_header +ktap_set_plan 28 + +# Without secbit configuration, nothing is changed. + +ktap_print_msg "By default, executable scripts are allowed to be interpreted and executed." +ktap_test exec_direct 0 script-exec.inc +ktap_test exec_indirect 0 script-exec.inc + +ktap_print_msg "By default, executable stdin is allowed to be interpreted." +ktap_test exec_stdin_reg 0 script-exec.inc + +ktap_print_msg "By default, non-executable scripts are allowed to be interpreted, but not directly executed." +# We get 126 because of direct execution by Bash. +ktap_test exec_direct 126 script-noexec.inc +ktap_test exec_indirect 0 script-noexec.inc + +ktap_print_msg "By default, non-executable stdin is allowed to be interpreted." +ktap_test exec_stdin_reg 0 script-noexec.inc + +ktap_print_msg "By default, interactive commands are allowed to be interpreted." +ktap_test exec_interactive 0 + +# With only file restriction: protect non-malicious users from inadvertent errors (e.g. python ~/Downloads/*.py). + +ktap_print_msg "With -f, executable scripts are allowed to be interpreted and executed." +ktap_test exec_direct 0 script-exec.inc ./set-exec -f -- +ktap_test exec_indirect 0 script-exec.inc ./set-exec -f -- + +ktap_print_msg "With -f, executable stdin is allowed to be interpreted." +ktap_test exec_stdin_reg 0 script-exec.inc ./set-exec -f -- + +ktap_print_msg "With -f, non-executable scripts are not allowed to be executed nor interpreted." +# Direct execution of non-executable script is alwayse denied by the kernel. +ktap_test exec_direct 1 script-noexec.inc ./set-exec -f -- +ktap_test exec_indirect 1 script-noexec.inc ./set-exec -f -- + +ktap_print_msg "With -f, non-executable stdin is allowed to be interpreted." +ktap_test exec_stdin_reg 0 script-noexec.inc ./set-exec -f -- + +ktap_print_msg "With -f, interactive commands are allowed to be interpreted." +ktap_test exec_interactive 0 ./set-exec -f -- + +# With only denied interactive commands: check or monitor script content (e.g. with LSM). + +ktap_print_msg "With -i, executable scripts are allowed to be interpreted and executed." +ktap_test exec_direct 0 script-exec.inc ./set-exec -i -- +ktap_test exec_indirect 0 script-exec.inc ./set-exec -i -- + +ktap_print_msg "With -i, executable stdin is allowed to be interpreted." +ktap_test exec_stdin_reg 0 script-exec.inc ./set-exec -i -- + +ktap_print_msg "With -i, non-executable scripts are allowed to be interpreted, but not directly executed." +# Direct execution of non-executable script is alwayse denied by the kernel. +ktap_test exec_direct 1 script-noexec.inc ./set-exec -i -- +ktap_test exec_indirect 0 script-noexec.inc ./set-exec -i -- + +ktap_print_msg "With -i, non-executable stdin is not allowed to be interpreted." +ktap_test exec_stdin_reg 1 script-noexec.inc ./set-exec -i -- + +ktap_print_msg "With -i, interactive commands are not allowed to be interpreted." +ktap_test exec_interactive 1 ./set-exec -i -- + +# With both file restriction and denied interactive commands: only allow executable scripts. + +ktap_print_msg "With -fi, executable scripts are allowed to be interpreted and executed." +ktap_test exec_direct 0 script-exec.inc ./set-exec -fi -- +ktap_test exec_indirect 0 script-exec.inc ./set-exec -fi -- + +ktap_print_msg "With -fi, executable stdin is allowed to be interpreted." +ktap_test exec_stdin_reg 0 script-exec.inc ./set-exec -fi -- + +ktap_print_msg "With -fi, non-executable scripts are not allowed to be interpreted nor executed." +# Direct execution of non-executable script is alwayse denied by the kernel. +ktap_test exec_direct 1 script-noexec.inc ./set-exec -fi -- +ktap_test exec_indirect 1 script-noexec.inc ./set-exec -fi -- + +ktap_print_msg "With -fi, non-executable stdin is not allowed to be interpreted." +ktap_test exec_stdin_reg 1 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Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=digikod.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b="gyVf2SmT" Received: from smtp-4-0001.mail.infomaniak.ch (smtp-4-0001.mail.infomaniak.ch [10.7.10.108]) by smtp-4-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4Y3zqs0MkxzrlZ; Thu, 5 Dec 2024 17:10:01 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1733415000; bh=q3iLh0+RYBxCd48+szjuBjIcYn8usj2ORomMH4nDYxc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gyVf2SmTbpZ4F0Fo3Tv2kKWTdUwLRWFx5sCpC+OgU8Ga0uwaNiL9rynsq0G+j9MXz TcXCsp3n54VduA412Q6Tx8DlZGxUR9YJNk/s3MhGtZxosGn/JO1+ZTHdjMpLG3mX42 dUijeWWbx5fdtSyaWs0iinWMQ/8LulBIaFnzd9i4= Received: from unknown by smtp-4-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4Y3zqq4648zhrT; Thu, 5 Dec 2024 17:09:59 +0100 (CET) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Al Viro , Christian Brauner , Kees Cook , Paul Moore , Serge Hallyn Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Adhemerval Zanella Netto , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Elliott Hughes , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Linus Torvalds , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Roberto Sassu , Scott Shell , Shuah Khan , Shuah Khan , Stephen Rothwell , Steve Dower , Steve Grubb , Theodore Ts'o , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH v22 8/8] ima: instantiate the bprm_creds_for_exec() hook Date: Thu, 5 Dec 2024 17:09:25 +0100 Message-ID: <20241205160925.230119-9-mic@digikod.net> In-Reply-To: <20241205160925.230119-1-mic@digikod.net> References: <20241205160925.230119-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha From: Mimi Zohar Like direct file execution (e.g. ./script.sh), indirect file execution (e.g. sh script.sh) needs to be measured and appraised. Instantiate the new security_bprm_creds_for_exec() hook to measure and verify the indirect file's integrity. Unlike direct file execution, indirect file execution is optionally enforced by the interpreter. Differentiate kernel and userspace enforced integrity audit messages. Co-developed-by: Roberto Sassu Signed-off-by: Roberto Sassu Signed-off-by: Mimi Zohar Link: https://lore.kernel.org/r/20241204192514.40308-1-zohar@linux.ibm.com Reviewed-by: Mickaël Salaün Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20241205160925.230119-9-mic@digikod.net --- I added both a Reviewed-by and a Signed-off-by because I may not be the committer. Changes since v21: * New patch cherry-picked from IMA's patch v3: https://lore.kernel.org/r/67b2e94f263bf9a0099efe74cce659d6acb16fe9.camel@linux.ibm.com * Fix a typo in comment: s/execvat/execveat/ . --- include/uapi/linux/audit.h | 1 + security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++++-- security/integrity/ima/ima_main.c | 29 +++++++++++++++++++++++++++ 3 files changed, 55 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h index 75e21a135483..826337905466 100644 --- a/include/uapi/linux/audit.h +++ b/include/uapi/linux/audit.h @@ -161,6 +161,7 @@ #define AUDIT_INTEGRITY_RULE 1805 /* policy rule */ #define AUDIT_INTEGRITY_EVM_XATTR 1806 /* New EVM-covered xattr */ #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */ +#define AUDIT_INTEGRITY_DATA_CHECK 1808 /* Userspace enforced data integrity */ #define AUDIT_KERNEL 2000 /* Asynchronous audit record. NOT A REQUEST. */ diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index 884a3533f7af..998c46c769d8 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include #include @@ -469,6 +470,17 @@ int ima_check_blacklist(struct ima_iint_cache *iint, return rc; } +static bool is_bprm_creds_for_exec(enum ima_hooks func, struct file *file) +{ + struct linux_binprm *bprm; + + if (func == BPRM_CHECK) { + bprm = container_of(&file, struct linux_binprm, file); + return bprm->is_check; + } + return false; +} + /* * ima_appraise_measurement - appraise file measurement * @@ -483,6 +495,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, int xattr_len, const struct modsig *modsig) { static const char op[] = "appraise_data"; + int audit_msgno = AUDIT_INTEGRITY_DATA; const char *cause = "unknown"; struct dentry *dentry = file_dentry(file); struct inode *inode = d_backing_inode(dentry); @@ -494,6 +507,16 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, if (!(inode->i_opflags & IOP_XATTR) && !try_modsig) return INTEGRITY_UNKNOWN; + /* + * Unlike any of the other LSM hooks where the kernel enforces file + * integrity, enforcing file integrity for the bprm_creds_for_exec() + * LSM hook with the AT_EXECVE_CHECK flag is left up to the discretion + * of the script interpreter(userspace). Differentiate kernel and + * userspace enforced integrity audit messages. + */ + if (is_bprm_creds_for_exec(func, file)) + audit_msgno = AUDIT_INTEGRITY_DATA_CHECK; + /* If reading the xattr failed and there's no modsig, error out. */ if (rc <= 0 && !try_modsig) { if (rc && rc != -ENODATA) @@ -569,7 +592,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) { status = INTEGRITY_FAIL; cause = "unverifiable-signature"; - integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename, + integrity_audit_msg(audit_msgno, inode, filename, op, cause, rc, 0); } else if (status != INTEGRITY_PASS) { /* Fix mode, but don't replace file signatures. */ @@ -589,7 +612,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, status = INTEGRITY_PASS; } - integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename, + integrity_audit_msg(audit_msgno, inode, filename, op, cause, rc, 0); } else { ima_cache_flags(iint, func); diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 9b87556b03a7..9f9897a7c217 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -554,6 +554,34 @@ static int ima_bprm_check(struct linux_binprm *bprm) MAY_EXEC, CREDS_CHECK); } +/** + * ima_bprm_creds_for_exec - collect/store/appraise measurement. + * @bprm: contains the linux_binprm structure + * + * Based on the IMA policy and the execveat(2) AT_EXECVE_CHECK flag, measure + * and appraise the integrity of a file to be executed by script interpreters. + * Unlike any of the other LSM hooks where the kernel enforces file integrity, + * enforcing file integrity is left up to the discretion of the script + * interpreter (userspace). + * + * On success return 0. On integrity appraisal error, assuming the file + * is in policy and IMA-appraisal is in enforcing mode, return -EACCES. + */ +static int ima_bprm_creds_for_exec(struct linux_binprm *bprm) +{ + /* + * As security_bprm_check() is called multiple times, both + * the script and the shebang interpreter are measured, appraised, + * and audited. Limit usage of this LSM hook to just measuring, + * appraising, and auditing the indirect script execution + * (e.g. ./sh example.sh). + */ + if (!bprm->is_check) + return 0; + + return ima_bprm_check(bprm); +} + /** * ima_file_check - based on policy, collect/store measurement. * @file: pointer to the file to be measured @@ -1174,6 +1202,7 @@ static int __init init_ima(void) static struct security_hook_list ima_hooks[] __ro_after_init = { LSM_HOOK_INIT(bprm_check_security, ima_bprm_check), + LSM_HOOK_INIT(bprm_creds_for_exec, ima_bprm_creds_for_exec), LSM_HOOK_INIT(file_post_open, ima_file_check), LSM_HOOK_INIT(inode_post_create_tmpfile, ima_post_create_tmpfile), LSM_HOOK_INIT(file_release, ima_file_free),