From patchwork Thu Jul 23 17:12:21 2020 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: 11681343 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 601A7722 for ; Thu, 23 Jul 2020 17:12:52 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id C741B22B40 for ; Thu, 23 Jul 2020 17:12:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C741B22B40 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19427-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 19949 invoked by uid 550); 23 Jul 2020 17:12:47 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 19888 invoked from network); 23 Jul 2020 17:12:47 -0000 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?utf-8?q?Philippe_Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v7 1/7] exec: Change uselib(2) IS_SREG() failure to EACCES Date: Thu, 23 Jul 2020 19:12:21 +0200 Message-Id: <20200723171227.446711-2-mic@digikod.net> X-Mailer: git-send-email 2.28.0.rc1 In-Reply-To: <20200723171227.446711-1-mic@digikod.net> References: <20200723171227.446711-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 From: Kees Cook Change uselib(2)' S_ISREG() error return to EACCES instead of EINVAL so the behavior matches execve(2), and the seemingly documented value. The "not a regular file" failure mode of execve(2) is explicitly documented[1], but it is not mentioned in uselib(2)[2] which does, however, say that open(2) and mmap(2) errors may apply. The documentation for open(2) does not include a "not a regular file" error[3], but mmap(2) does[4], and it is EACCES. [1] http://man7.org/linux/man-pages/man2/execve.2.html#ERRORS [2] http://man7.org/linux/man-pages/man2/uselib.2.html#ERRORS [3] http://man7.org/linux/man-pages/man2/open.2.html#ERRORS [4] http://man7.org/linux/man-pages/man2/mmap.2.html#ERRORS Signed-off-by: Mickaël Salaün Signed-off-by: Kees Cook Acked-by: Christian Brauner Link: https://lore.kernel.org/r/20200605160013.3954297-2-keescook@chromium.org --- fs/exec.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index e6e8a9a70327..d7c937044d10 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -141,11 +141,10 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) if (IS_ERR(file)) goto out; - error = -EINVAL; + error = -EACCES; if (!S_ISREG(file_inode(file)->i_mode)) goto exit; - error = -EACCES; if (path_noexec(&file->f_path)) goto exit; From patchwork Thu Jul 23 17:12:22 2020 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: 11681353 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D6281722 for ; Thu, 23 Jul 2020 17:13:02 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 1F75522B40 for ; Thu, 23 Jul 2020 17:13:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F75522B40 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19428-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 20103 invoked by uid 550); 23 Jul 2020 17:12:49 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 20027 invoked from network); 23 Jul 2020 17:12:48 -0000 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?utf-8?q?Philippe_Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v7 2/7] exec: Move S_ISREG() check earlier Date: Thu, 23 Jul 2020 19:12:22 +0200 Message-Id: <20200723171227.446711-3-mic@digikod.net> X-Mailer: git-send-email 2.28.0.rc1 In-Reply-To: <20200723171227.446711-1-mic@digikod.net> References: <20200723171227.446711-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 From: Kees Cook The execve(2)/uselib(2) syscalls have always rejected non-regular files. Recently, it was noticed that a deadlock was introduced when trying to execute pipes, as the S_ISREG() test was happening too late. This was fixed in commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files during execve()"), but it was added after inode_permission() had already run, which meant LSMs could see bogus attempts to execute non-regular files. Move the test into the other inode type checks (which already look for other pathological conditions[1]). Since there is no need to use FMODE_EXEC while we still have access to "acc_mode", also switch the test to MAY_EXEC. Also include a comment with the redundant S_ISREG() checks at the end of execve(2)/uselib(2) to note that they are present to avoid any mistakes. My notes on the call path, and related arguments, checks, etc: do_open_execat() struct open_flags open_exec_flags = { .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, .acc_mode = MAY_EXEC, ... do_filp_open(dfd, filename, open_flags) path_openat(nameidata, open_flags, flags) file = alloc_empty_file(open_flags, current_cred()); do_open(nameidata, file, open_flags) may_open(path, acc_mode, open_flag) /* new location of MAY_EXEC vs S_ISREG() test */ inode_permission(inode, MAY_OPEN | acc_mode) security_inode_permission(inode, acc_mode) vfs_open(path, file) do_dentry_open(file, path->dentry->d_inode, open) /* old location of FMODE_EXEC vs S_ISREG() test */ security_file_open(f) open() [1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/ Signed-off-by: Mickaël Salaün Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org --- fs/exec.c | 14 ++++++++++++-- fs/namei.c | 6 ++++-- fs/open.c | 6 ------ 3 files changed, 16 insertions(+), 10 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index d7c937044d10..bdc6a6eb5dce 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -141,8 +141,13 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) if (IS_ERR(file)) goto out; + /* + * may_open() has already checked for this, so it should be + * impossible to trip now. But we need to be extra cautious + * and check again at the very end too. + */ error = -EACCES; - if (!S_ISREG(file_inode(file)->i_mode)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) goto exit; if (path_noexec(&file->f_path)) @@ -886,8 +891,13 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) if (IS_ERR(file)) goto out; + /* + * may_open() has already checked for this, so it should be + * impossible to trip now. But we need to be extra cautious + * and check again at the very end too. + */ err = -EACCES; - if (!S_ISREG(file_inode(file)->i_mode)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) goto exit; if (path_noexec(&file->f_path)) diff --git a/fs/namei.c b/fs/namei.c index 72d4219c93ac..a559ad943970 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2849,16 +2849,18 @@ static int may_open(const struct path *path, int acc_mode, int flag) case S_IFLNK: return -ELOOP; case S_IFDIR: - if (acc_mode & MAY_WRITE) + if (acc_mode & (MAY_WRITE | MAY_EXEC)) return -EISDIR; break; case S_IFBLK: case S_IFCHR: if (!may_open_dev(path)) return -EACCES; - /*FALLTHRU*/ + fallthrough; case S_IFIFO: case S_IFSOCK: + if (acc_mode & MAY_EXEC) + return -EACCES; flag &= ~O_TRUNC; break; } diff --git a/fs/open.c b/fs/open.c index 6cd48a61cda3..623b7506a6db 100644 --- a/fs/open.c +++ b/fs/open.c @@ -784,12 +784,6 @@ static int do_dentry_open(struct file *f, return 0; } - /* Any file opened for execve()/uselib() has to be a regular file. */ - if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) { - error = -EACCES; - goto cleanup_file; - } - if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) { error = get_write_access(inode); if (unlikely(error)) From patchwork Thu Jul 23 17:12:23 2020 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: 11681359 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 163D8138C for ; Thu, 23 Jul 2020 17:13:11 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 7BE2222B47 for ; Thu, 23 Jul 2020 17:13:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7BE2222B47 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19429-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 20251 invoked by uid 550); 23 Jul 2020 17:12:51 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 20191 invoked from network); 23 Jul 2020 17:12:50 -0000 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?utf-8?q?Philippe_Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v7 3/7] exec: Move path_noexec() check earlier Date: Thu, 23 Jul 2020 19:12:23 +0200 Message-Id: <20200723171227.446711-4-mic@digikod.net> X-Mailer: git-send-email 2.28.0.rc1 In-Reply-To: <20200723171227.446711-1-mic@digikod.net> References: <20200723171227.446711-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 From: Kees Cook The path_noexec() check, like the regular file check, was happening too late, letting LSMs see impossible execve()s. Check it earlier as well in may_open() and collect the redundant fs/exec.c path_noexec() test under the same robustness comment as the S_ISREG() check. My notes on the call path, and related arguments, checks, etc: do_open_execat() struct open_flags open_exec_flags = { .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, .acc_mode = MAY_EXEC, ... do_filp_open(dfd, filename, open_flags) path_openat(nameidata, open_flags, flags) file = alloc_empty_file(open_flags, current_cred()); do_open(nameidata, file, open_flags) may_open(path, acc_mode, open_flag) /* new location of MAY_EXEC vs path_noexec() test */ inode_permission(inode, MAY_OPEN | acc_mode) security_inode_permission(inode, acc_mode) vfs_open(path, file) do_dentry_open(file, path->dentry->d_inode, open) security_file_open(f) open() /* old location of path_noexec() test */ Signed-off-by: Mickaël Salaün Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org --- fs/exec.c | 12 ++++-------- fs/namei.c | 4 ++++ 2 files changed, 8 insertions(+), 8 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index bdc6a6eb5dce..4eea20c27b01 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) * and check again at the very end too. */ error = -EACCES; - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) - goto exit; - - if (path_noexec(&file->f_path)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || + path_noexec(&file->f_path))) goto exit; fsnotify_open(file); @@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) * and check again at the very end too. */ err = -EACCES; - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) - goto exit; - - if (path_noexec(&file->f_path)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || + path_noexec(&file->f_path))) goto exit; err = deny_write_access(file); diff --git a/fs/namei.c b/fs/namei.c index a559ad943970..ddc9b25540fe 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag) return -EACCES; flag &= ~O_TRUNC; break; + case S_IFREG: + if ((acc_mode & MAY_EXEC) && path_noexec(path)) + return -EACCES; + break; } error = inode_permission(inode, MAY_OPEN | acc_mode); From patchwork Thu Jul 23 17:12:24 2020 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: 11681369 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 47AF5138C for ; Thu, 23 Jul 2020 17:13:20 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 83DBC22B47 for ; Thu, 23 Jul 2020 17:13:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 83DBC22B47 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19430-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 20377 invoked by uid 550); 23 Jul 2020 17:12:53 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 20317 invoked from network); 23 Jul 2020 17:12:51 -0000 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?utf-8?q?Philippe_Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, Thibaut Sautereau Subject: [PATCH v7 4/7] fs: Introduce O_MAYEXEC flag for openat2(2) Date: Thu, 23 Jul 2020 19:12:24 +0200 Message-Id: <20200723171227.446711-5-mic@digikod.net> X-Mailer: git-send-email 2.28.0.rc1 In-Reply-To: <20200723171227.446711-1-mic@digikod.net> References: <20200723171227.446711-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 When the O_MAYEXEC flag is passed, openat2(2) may be subject to additional restrictions depending on a security policy managed by the kernel through a sysctl or implemented by an LSM thanks to the inode_permission hook. This new flag is ignored by open(2) and openat(2) because of their unspecified flags handling. When used with openat2(2), the default behavior is only to forbid to open a directory. The underlying idea is to be able to restrict scripts interpretation according to a policy defined by the system administrator. For this to be possible, script interpreters must use the O_MAYEXEC flag appropriately. To be fully effective, these interpreters also need to handle the other ways to execute code: command line parameters (e.g., option -e for Perl), module loading (e.g., option -m for Python), stdin, file sourcing, environment variables, configuration files, etc. According to the threat model, it may be acceptable to allow some script interpreters (e.g. Bash) to interpret commands from stdin, may it be a TTY or a pipe, because it may not be enough to (directly) perform syscalls. Further documentation can be found in a following patch. Even without enforced security policy, userland interpreters can set it to enforce the system policy at their level, knowing that it will not break anything on running systems which do not care about this feature. However, on systems which want this feature enforced, there will be knowledgeable people (i.e. sysadmins who enforced O_MAYEXEC deliberately) to manage it. A simple security policy implementation, configured through a dedicated sysctl, is available in a following patch. O_MAYEXEC should not be confused with the O_EXEC flag which is intended for execute-only, which obviously doesn't work for scripts. However, a similar behavior could be implemented in userland with O_PATH: https://lore.kernel.org/lkml/1e2f6913-42f2-3578-28ed-567f6a4bdda1@digikod.net/ The implementation of O_MAYEXEC almost duplicates what execve(2) and uselib(2) are already doing: setting MAY_OPENEXEC in acc_mode (which can then be checked as MAY_EXEC, if enforced). This is an updated subset of the patch initially written by Vincent Strubel for CLIP OS 4: https://github.com/clipos-archive/src_platform_clip-patches/blob/f5cb330d6b684752e403b4e41b39f7004d88e561/1901_open_mayexec.patch This patch has been used for more than 12 years with customized script interpreters. Some examples (with the original O_MAYEXEC) can be found here: https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC Co-developed-by: Vincent Strubel Signed-off-by: Vincent Strubel Co-developed-by: Thibaut Sautereau Signed-off-by: Thibaut Sautereau Signed-off-by: Mickaël Salaün Cc: Aleksa Sarai Cc: Al Viro Cc: Deven Bowers Cc: Kees Cook Acked-by: Kees Cook --- Changes since v6: * Do not set __FMODE_EXEC for now because of inconsistent behavior: https://lore.kernel.org/lkml/202007160822.CCDB5478@keescook/ * Returns EISDIR when opening a directory with O_MAYEXEC. * Removed Deven Bowers and Kees Cook Reviewed-by tags because of the current update. Changes since v5: * Update commit message. Changes since v3: * Switch back to O_MAYEXEC, but only handle it with openat2(2) which checks unknown flags (suggested by Aleksa Sarai). Cf. https://lore.kernel.org/lkml/20200430015429.wuob7m5ofdewubui@yavin.dot.cyphar.com/ Changes since v2: * Replace O_MAYEXEC with RESOLVE_MAYEXEC from openat2(2). This change enables to not break existing application using bogus O_* flags that may be ignored by current kernels by using a new dedicated flag, only usable through openat2(2) (suggested by Jeff Layton). Using this flag will results in an error if the running kernel does not support it. User space needs to manage this case, as with other RESOLVE_* flags. The best effort approach to security (for most common distros) will simply consists of ignoring such an error and retry without RESOLVE_MAYEXEC. However, a fully controlled system may which to error out if such an inconsistency is detected. Changes since v1: * Set __FMODE_EXEC when using O_MAYEXEC to make this information available through the new fanotify/FAN_OPEN_EXEC event (suggested by Jan Kara and Matthew Bobrowski): https://lore.kernel.org/lkml/20181213094658.GA996@lithium.mbobrowski.org/ --- fs/fcntl.c | 2 +- fs/namei.c | 4 ++-- fs/open.c | 6 ++++++ include/linux/fcntl.h | 2 +- include/linux/fs.h | 2 ++ include/uapi/asm-generic/fcntl.h | 7 +++++++ 6 files changed, 19 insertions(+), 4 deletions(-) diff --git a/fs/fcntl.c b/fs/fcntl.c index 2e4c0fa2074b..0357ad667563 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -1033,7 +1033,7 @@ static int __init fcntl_init(void) * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY * is defined as O_NONBLOCK on some platforms and not on others. */ - BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ != + BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32( (VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) | __FMODE_EXEC | __FMODE_NONOTIFY)); diff --git a/fs/namei.c b/fs/namei.c index ddc9b25540fe..3f074ec77390 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -428,7 +428,7 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask) /** * inode_permission - Check for access rights to a given inode * @inode: Inode to check permission on - * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) + * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, %MAY_OPENEXEC) * * Check for read/write/execute permissions on an inode. We use fs[ug]id for * this, letting us set arbitrary permissions for filesystem access without @@ -2849,7 +2849,7 @@ static int may_open(const struct path *path, int acc_mode, int flag) case S_IFLNK: return -ELOOP; case S_IFDIR: - if (acc_mode & (MAY_WRITE | MAY_EXEC)) + if (acc_mode & (MAY_WRITE | MAY_EXEC | MAY_OPENEXEC)) return -EISDIR; break; case S_IFBLK: diff --git a/fs/open.c b/fs/open.c index 623b7506a6db..21c2c1020574 100644 --- a/fs/open.c +++ b/fs/open.c @@ -987,6 +987,8 @@ inline struct open_how build_open_how(int flags, umode_t mode) .mode = mode & S_IALLUGO, }; + /* O_MAYEXEC is ignored by syscalls relying on build_open_how(). */ + how.flags &= ~O_MAYEXEC; /* O_PATH beats everything else. */ if (how.flags & O_PATH) how.flags &= O_PATH_FLAGS; @@ -1054,6 +1056,10 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op) if (flags & __O_SYNC) flags |= O_DSYNC; + /* Checks execution permissions on open. */ + if (flags & O_MAYEXEC) + acc_mode |= MAY_OPENEXEC; + op->open_flag = flags; /* O_TRUNC implies we need access checks for write permissions */ diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index 7bcdcf4f6ab2..e188a360fa5f 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -10,7 +10,7 @@ (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \ O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __O_SYNC | O_DSYNC | \ FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ - O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) + O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_MAYEXEC) /* List of all valid flags for the how->upgrade_mask argument: */ #define VALID_UPGRADE_FLAGS \ diff --git a/include/linux/fs.h b/include/linux/fs.h index f5abba86107d..56f835c9a87a 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -101,6 +101,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, #define MAY_CHDIR 0x00000040 /* called from RCU mode, don't block */ #define MAY_NOT_BLOCK 0x00000080 +/* the inode is opened with O_MAYEXEC */ +#define MAY_OPENEXEC 0x00000100 /* * flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h index 9dc0bf0c5a6e..bca90620119f 100644 --- a/include/uapi/asm-generic/fcntl.h +++ b/include/uapi/asm-generic/fcntl.h @@ -97,6 +97,13 @@ #define O_NDELAY O_NONBLOCK #endif +/* + * Code execution from file is intended, checks such permission. A simple + * policy can be enforced system-wide as explained in + * Documentation/admin-guide/sysctl/fs.rst . + */ +#define O_MAYEXEC 040000000 + #define F_DUPFD 0 /* dup */ #define F_GETFD 1 /* get close_on_exec */ #define F_SETFD 2 /* set/clear close_on_exec */ From patchwork Thu Jul 23 17:12:25 2020 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: 11681383 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A8BB5722 for ; Thu, 23 Jul 2020 17:13:30 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id B850C22B47 for ; Thu, 23 Jul 2020 17:13:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B850C22B47 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19431-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 21506 invoked by uid 550); 23 Jul 2020 17:12:55 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 20351 invoked from network); 23 Jul 2020 17:12:53 -0000 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?utf-8?q?Philippe_Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, Thibaut Sautereau , Randy Dunlap Subject: [PATCH v7 5/7] fs,doc: Enable to enforce noexec mounts or file exec through O_MAYEXEC Date: Thu, 23 Jul 2020 19:12:25 +0200 Message-Id: <20200723171227.446711-6-mic@digikod.net> X-Mailer: git-send-email 2.28.0.rc1 In-Reply-To: <20200723171227.446711-1-mic@digikod.net> References: <20200723171227.446711-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 Allow for the enforcement of the O_MAYEXEC openat2(2) flag. Thanks to the noexec option from the underlying VFS mount, or to the file execute permission, userspace can enforce these execution policies. This may allow script interpreters to check execution permission before reading commands from a file, or dynamic linkers to allow shared object loading. Add a new sysctl fs.open_mayexec_enforce to enable system administrators to enforce two complementary security policies according to the installed system: enforce the noexec mount option, and enforce executable file permission. Indeed, because of compatibility with installed systems, only system administrators are able to check that this new enforcement is in line with the system mount points and file permissions. A following patch adds documentation. Being able to restrict execution also enables to protect the kernel by restricting arbitrary syscalls that an attacker could perform with a crafted binary or certain script languages. It also improves multilevel isolation by reducing the ability of an attacker to use side channels with specific code. These restrictions can natively be enforced for ELF binaries (with the noexec mount option) but require this kernel extension to properly handle scripts (e.g., Python, Perl). To get a consistent execution policy, additional memory restrictions should also be enforced (e.g. thanks to SELinux). Because the O_MAYEXEC flag is a meant to enforce a system-wide security policy (but not application-centric policies), it does not make sense for userland to check the sysctl value. Indeed, this new flag only enables to extend the system ability to enforce a policy thanks to (some trusted) userland collaboration. Moreover, additional security policies could be managed by LSMs. This is a best-effort approach from the application developer point of view: https://lore.kernel.org/lkml/1477d3d7-4b36-afad-7077-a38f42322238@digikod.net/ Signed-off-by: Mickaël Salaün Reviewed-by: Thibaut Sautereau Cc: Aleksa Sarai Cc: Al Viro Cc: Jonathan Corbet Cc: Kees Cook Cc: Randy Dunlap Acked-by: Kees Cook --- Changes since v6: * Allow opening pipes, block devices and character devices with O_MAYEXEC when there is no enforced policy, but forbid any non-regular file opened with O_MAYEXEC otherwise (i.e. for any enforced policy). * Add a paragraph about the non-regular files policy. * Move path_noexec() calls out of the fast-path (suggested by Kees Cook). Changes since v5: * Remove the static enforcement configuration through Kconfig because it makes the code more simple like this, and because the current sysctl configuration can only be set with CAP_SYS_ADMIN, the same way mount options (i.e. noexec) can be set. If an harden distro wants to enforce a configuration, it should restrict capabilities or sysctl configuration. Furthermore, an LSM can easily leverage O_MAYEXEC to fit its need. * Move checks from inode_permission() to may_open() and make the error codes more consistent according to file types (in line with a previous commit): opening a directory with O_MAYEXEC returns EISDIR and other non-regular file types may return EACCES. * In may_open(), when OMAYEXEC_ENFORCE_FILE is set, replace explicit call to generic_permission() with an artificial MAY_EXEC to avoid double calls. This makes sense especially when an LSM policy forbids execution of a file. * Replace the custom proc_omayexec() with proc_dointvec_minmax_sysadmin(), and then replace the CAP_MAC_ADMIN check with a CAP_SYS_ADMIN one (suggested by Kees Cook and Stephen Smalley). * Use BIT() (suggested by Kees Cook). * Rename variables (suggested by Kees Cook). * Reword the kconfig help. * Import the documentation patch (suggested by Kees Cook): https://lore.kernel.org/lkml/20200505153156.925111-6-mic@digikod.net/ * Update documentation and add LWN.net article. Changes since v4: * Add kernel configuration options to enforce O_MAYEXEC at build time, and disable the sysctl in such case (requested by James Morris). * Reword commit message. Changes since v3: * Update comment with O_MAYEXEC. Changes since v2: * Cosmetic changes. Changes since v1: * Move code from Yama to the FS subsystem (suggested by Kees Cook). * Make omayexec_inode_permission() static (suggested by Jann Horn). * Use mode 0600 for the sysctl. * Only match regular files (not directories nor other types), which follows the same semantic as commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files during execve()"). --- Documentation/admin-guide/sysctl/fs.rst | 49 +++++++++++++++++++++++++ fs/namei.c | 24 ++++++++++++ include/linux/fs.h | 1 + kernel/sysctl.c | 12 +++++- 4 files changed, 84 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/sysctl/fs.rst b/Documentation/admin-guide/sysctl/fs.rst index 2a45119e3331..ce6e2081d3a9 100644 --- a/Documentation/admin-guide/sysctl/fs.rst +++ b/Documentation/admin-guide/sysctl/fs.rst @@ -37,6 +37,7 @@ Currently, these files are in /proc/sys/fs: - inode-nr - inode-state - nr_open +- open_mayexec_enforce - overflowuid - overflowgid - pipe-user-pages-hard @@ -165,6 +166,54 @@ system needs to prune the inode list instead of allocating more. +open_mayexec_enforce +-------------------- + +While being ignored by :manpage:`open(2)` and :manpage:`openat(2)`, the +``O_MAYEXEC`` flag can be passed to :manpage:`openat2(2)` to only open regular +files that are expected to be executable. If the file is not identified as +executable, then the syscall returns -EACCES. This may allow a script +interpreter to check executable permission before reading commands from a file, +or a dynamic linker to only load executable shared objects. One interesting +use case is to enforce a "write xor execute" policy through interpreters. + +The ability to restrict code execution must be thought as a system-wide policy, +which first starts by restricting mount points with the ``noexec`` option. +This option is also automatically applied to special filesystems such as /proc . +This prevents files on such mount points to be directly executed by the kernel +or mapped as executable memory (e.g. libraries). With script interpreters +using the ``O_MAYEXEC`` flag, the executable permission can then be checked +before reading commands from files. This makes it possible to enforce the +``noexec`` at the interpreter level, and thus propagates this security policy +to scripts. To be fully effective, these interpreters also need to handle the +other ways to execute code: command line parameters (e.g., option ``-e`` for +Perl), module loading (e.g., option ``-m`` for Python), stdin, file sourcing, +environment variables, configuration files, etc. According to the threat +model, it may be acceptable to allow some script interpreters (e.g. Bash) to +interpret commands from stdin, may it be a TTY or a pipe, because it may not be +enough to (directly) perform syscalls. + +There are two complementary security policies: enforce the ``noexec`` mount +option, and enforce executable file permission. These policies are handled by +the ``fs.open_mayexec_enforce`` sysctl (writable only with ``CAP_SYS_ADMIN``) +as a bitmask: + +1 - Mount restriction: checks that the mount options for the underlying VFS + mount do not prevent execution. + +2 - File permission restriction: checks that the to-be-opened file is marked as + executable for the current process (e.g., POSIX permissions). + +Note that as long as a policy is enforced, opening any non-regular file with +``O_MAYEXEC`` is denied (e.g. TTYs, pipe), even when such a file is marked as +executable or is on an executable mount point. + +Code samples can be found in tools/testing/selftests/openat2/omayexec_test.c +and interpreter patches (for the original O_MAYEXEC version) may be found at +https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC . +See also an overview article: https://lwn.net/Articles/820000/ . + + overflowgid & overflowuid ------------------------- diff --git a/fs/namei.c b/fs/namei.c index 3f074ec77390..8ec13c7fd403 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -39,6 +39,7 @@ #include #include #include +#include #include "internal.h" #include "mount.h" @@ -425,6 +426,11 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask) return 0; } +#define OPEN_MAYEXEC_ENFORCE_MOUNT BIT(0) +#define OPEN_MAYEXEC_ENFORCE_FILE BIT(1) + +int sysctl_open_mayexec_enforce __read_mostly; + /** * inode_permission - Check for access rights to a given inode * @inode: Inode to check permission on @@ -2861,11 +2867,29 @@ static int may_open(const struct path *path, int acc_mode, int flag) case S_IFSOCK: if (acc_mode & MAY_EXEC) return -EACCES; + /* + * Opening devices (e.g. TTYs) or pipes with O_MAYEXEC may be + * legitimate when there is no enforced policy. + */ + if ((acc_mode & MAY_OPENEXEC) && sysctl_open_mayexec_enforce) + return -EACCES; flag &= ~O_TRUNC; break; case S_IFREG: if ((acc_mode & MAY_EXEC) && path_noexec(path)) return -EACCES; + if (acc_mode & MAY_OPENEXEC) { + if ((sysctl_open_mayexec_enforce & OPEN_MAYEXEC_ENFORCE_MOUNT) + && path_noexec(path)) + return -EACCES; + if (sysctl_open_mayexec_enforce & OPEN_MAYEXEC_ENFORCE_FILE) + /* + * Because acc_mode may change here, the next and only + * use of acc_mode should then be by the following call + * to inode_permission(). + */ + acc_mode |= MAY_EXEC; + } break; } diff --git a/include/linux/fs.h b/include/linux/fs.h index 56f835c9a87a..071f37707ccc 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -83,6 +83,7 @@ extern int sysctl_protected_symlinks; extern int sysctl_protected_hardlinks; extern int sysctl_protected_fifos; extern int sysctl_protected_regular; +extern int sysctl_open_mayexec_enforce; typedef __kernel_rwf_t rwf_t; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index db1ce7af2563..5008a2566e79 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -113,6 +113,7 @@ static int sixty = 60; static int __maybe_unused neg_one = -1; static int __maybe_unused two = 2; +static int __maybe_unused three = 3; static int __maybe_unused four = 4; static unsigned long zero_ul; static unsigned long one_ul = 1; @@ -888,7 +889,6 @@ static int proc_taint(struct ctl_table *table, int write, return err; } -#ifdef CONFIG_PRINTK static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { @@ -897,7 +897,6 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write, return proc_dointvec_minmax(table, write, buffer, lenp, ppos); } -#endif /** * struct do_proc_dointvec_minmax_conv_param - proc_dointvec_minmax() range checking structure @@ -3264,6 +3263,15 @@ static struct ctl_table fs_table[] = { .extra1 = SYSCTL_ZERO, .extra2 = &two, }, + { + .procname = "open_mayexec_enforce", + .data = &sysctl_open_mayexec_enforce, + .maxlen = sizeof(int), + .mode = 0600, + .proc_handler = proc_dointvec_minmax_sysadmin, + .extra1 = SYSCTL_ZERO, + .extra2 = &three, + }, #if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE) { .procname = "binfmt_misc", From patchwork Thu Jul 23 17:12:26 2020 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: 11681385 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 11BEB138C for ; Thu, 23 Jul 2020 17:13:43 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 2373D22BF3 for ; Thu, 23 Jul 2020 17:13:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2373D22BF3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19432-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 21650 invoked by uid 550); 23 Jul 2020 17:12:56 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 21507 invoked from network); 23 Jul 2020 17:12:55 -0000 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?utf-8?q?Philippe_Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, Thibaut Sautereau Subject: [PATCH v7 6/7] selftest/openat2: Add tests for O_MAYEXEC enforcing Date: Thu, 23 Jul 2020 19:12:26 +0200 Message-Id: <20200723171227.446711-7-mic@digikod.net> X-Mailer: git-send-email 2.28.0.rc1 In-Reply-To: <20200723171227.446711-1-mic@digikod.net> References: <20200723171227.446711-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 Test propagation of noexec mount points or file executability through files open with or without O_MAYEXEC, thanks to the fs.open_mayexec_enforce sysctl. Signed-off-by: Mickaël Salaün Reviewed-by: Thibaut Sautereau Cc: Aleksa Sarai Cc: Al Viro Cc: Kees Cook Cc: Shuah Khan Reviewed-by: Kees Cook --- 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/kselftest_harness.h | 3 + tools/testing/selftests/openat2/Makefile | 3 +- tools/testing/selftests/openat2/config | 1 + tools/testing/selftests/openat2/helpers.h | 1 + .../testing/selftests/openat2/omayexec_test.c | 325 ++++++++++++++++++ 5 files changed, 332 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/openat2/config create mode 100644 tools/testing/selftests/openat2/omayexec_test.c diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h index c9f03ef93338..68a0acd9ea1e 100644 --- a/tools/testing/selftests/kselftest_harness.h +++ b/tools/testing/selftests/kselftest_harness.h @@ -50,7 +50,10 @@ #ifndef __KSELFTEST_HARNESS_H #define __KSELFTEST_HARNESS_H +#ifndef _GNU_SOURCE #define _GNU_SOURCE +#endif + #include #include #include diff --git a/tools/testing/selftests/openat2/Makefile b/tools/testing/selftests/openat2/Makefile index 4b93b1417b86..cb98bdb4d5b1 100644 --- a/tools/testing/selftests/openat2/Makefile +++ b/tools/testing/selftests/openat2/Makefile @@ -1,7 +1,8 @@ # SPDX-License-Identifier: GPL-2.0-or-later CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined -TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test +LDLIBS += -lcap +TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test omayexec_test include ../lib.mk diff --git a/tools/testing/selftests/openat2/config b/tools/testing/selftests/openat2/config new file mode 100644 index 000000000000..dd53c266bf52 --- /dev/null +++ b/tools/testing/selftests/openat2/config @@ -0,0 +1 @@ +CONFIG_SYSCTL=y diff --git a/tools/testing/selftests/openat2/helpers.h b/tools/testing/selftests/openat2/helpers.h index a6ea27344db2..1dcd3e1e2f38 100644 --- a/tools/testing/selftests/openat2/helpers.h +++ b/tools/testing/selftests/openat2/helpers.h @@ -9,6 +9,7 @@ #define _GNU_SOURCE #include +#include #include #include #include "../kselftest.h" diff --git a/tools/testing/selftests/openat2/omayexec_test.c b/tools/testing/selftests/openat2/omayexec_test.c new file mode 100644 index 000000000000..34b91f9d78d0 --- /dev/null +++ b/tools/testing/selftests/openat2/omayexec_test.c @@ -0,0 +1,325 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Test O_MAYEXEC + * + * Copyright © 2018-2020 ANSSI + * + * Author: Mickaël Salaün + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "helpers.h" +#include "../kselftest_harness.h" + +#ifndef O_MAYEXEC +#define O_MAYEXEC 040000000 +#endif + +static const char sysctl_path[] = "/proc/sys/fs/open_mayexec_enforce"; + +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 symlink_path[] = "./test-mount/symlink"; +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"; +static const char sock_path[] = "./test-mount/socket"; + +static void ignore_dac(struct __test_metadata *_metadata, int override) +{ + cap_t caps; + const cap_value_t cap_val[2] = { + CAP_DAC_OVERRIDE, + CAP_DAC_READ_SEARCH, + }; + + caps = cap_get_proc(); + ASSERT_NE(NULL, caps); + ASSERT_EQ(0, cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_val, + override ? CAP_SET : CAP_CLEAR)); + ASSERT_EQ(0, cap_set_proc(caps)); + EXPECT_EQ(0, cap_free(caps)); +} + +static void ignore_sys_admin(struct __test_metadata *_metadata, int override) +{ + cap_t caps; + const cap_value_t cap_val[1] = { + CAP_SYS_ADMIN, + }; + + caps = cap_get_proc(); + ASSERT_NE(NULL, caps); + ASSERT_EQ(0, cap_set_flag(caps, CAP_EFFECTIVE, 1, cap_val, + override ? CAP_SET : CAP_CLEAR)); + ASSERT_EQ(0, cap_set_proc(caps)); + EXPECT_EQ(0, cap_free(caps)); +} + +static void test_omx(struct __test_metadata *_metadata, + const char *const path, const int no_mayexec_err_code, + const int mayexec_err_code) +{ + struct open_how how = { + .flags = O_RDONLY | O_NOFOLLOW | O_CLOEXEC, + }; + int fd; + + /* Do not block on pipes. */ + if (path == fifo_path) + how.flags |= O_NONBLOCK; + + /* Opens without O_MAYEXEC. */ + fd = sys_openat2(AT_FDCWD, path, &how); + if (!no_mayexec_err_code) { + ASSERT_LE(0, fd) { + TH_LOG("Failed to openat2 %s: %d", path, -fd); + } + EXPECT_EQ(0, close(fd)); + } else { + ASSERT_EQ(no_mayexec_err_code, fd) { + TH_LOG("Wrong error for openat2 %s: %d", path, -fd); + } + } + + how.flags |= O_MAYEXEC; + + /* Checks that O_MAYEXEC is ignored with open(2). */ + fd = open(path, how.flags); + if (!no_mayexec_err_code) { + ASSERT_LE(0, fd) { + TH_LOG("Failed to open %s: %d", path, errno); + } + EXPECT_EQ(0, close(fd)); + } else { + ASSERT_EQ(no_mayexec_err_code, -errno); + } + + /* Checks that O_MAYEXEC is ignored with openat(2). */ + fd = openat(AT_FDCWD, path, how.flags); + if (!no_mayexec_err_code) { + ASSERT_LE(0, fd) { + TH_LOG("Failed to openat %s: %d", path, errno); + } + EXPECT_EQ(0, close(fd)); + } else { + ASSERT_EQ(no_mayexec_err_code, -errno); + } + + /* Opens with O_MAYEXEC. */ + fd = sys_openat2(AT_FDCWD, path, &how); + if (!mayexec_err_code) { + ASSERT_LE(0, fd) { + TH_LOG("Failed to openat2 %s: %d", path, -fd); + } + EXPECT_EQ(0, close(fd)); + } else { + ASSERT_EQ(mayexec_err_code, fd) { + TH_LOG("Wrong error for openat2 %s: %d", path, -fd); + } + } +} + +static void test_file_types(struct __test_metadata *_metadata, const int err_code, + const bool has_policy) +{ + test_omx(_metadata, reg_file_path, 0, err_code); + test_omx(_metadata, dir_path, 0, -EISDIR); + test_omx(_metadata, symlink_path, -ELOOP, -ELOOP); + test_omx(_metadata, block_dev_path, 0, has_policy ? -EACCES : 0); + test_omx(_metadata, char_dev_path, 0, has_policy ? -EACCES : 0); + test_omx(_metadata, fifo_path, 0, has_policy ? -EACCES : 0); + test_omx(_metadata, sock_path, -ENXIO, has_policy ? -EACCES : -ENXIO); +} + +static void test_files(struct __test_metadata *_metadata, const int err_code, + const bool has_policy) +{ + /* Tests as root. */ + ignore_dac(_metadata, 1); + test_file_types(_metadata, err_code, has_policy); + + /* Tests without bypass. */ + ignore_dac(_metadata, 0); + test_file_types(_metadata, err_code, has_policy); +} + +static void sysctl_write_char(struct __test_metadata *_metadata, const char value) +{ + int fd; + + fd = open(sysctl_path, O_WRONLY | O_CLOEXEC); + ASSERT_LE(0, fd); + ASSERT_EQ(1, write(fd, &value, 1)); + EXPECT_EQ(0, close(fd)); +} + +static char sysctl_read_char(struct __test_metadata *_metadata) +{ + int fd; + char sysctl_value; + + fd = open(sysctl_path, O_RDONLY | O_CLOEXEC); + ASSERT_LE(0, fd); + ASSERT_EQ(1, read(fd, &sysctl_value, 1)); + EXPECT_EQ(0, close(fd)); + return sysctl_value; +} + +FIXTURE(omayexec) { + char initial_sysctl_value; +}; + +FIXTURE_VARIANT(omayexec) { + const bool mount_exec; + const bool file_exec; + const int sysctl_err_code[3]; +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_exec_file_exec) { + .mount_exec = true, + .file_exec = true, + .sysctl_err_code = {0, 0, 0}, +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_exec_file_noexec) +{ + .mount_exec = true, + .file_exec = false, + .sysctl_err_code = {0, -EACCES, -EACCES}, +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_noexec_file_exec) +{ + .mount_exec = false, + .file_exec = true, + .sysctl_err_code = {-EACCES, 0, -EACCES}, +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_noexec_file_noexec) +{ + .mount_exec = false, + .file_exec = false, + .sysctl_err_code = {-EACCES, -EACCES, -EACCES}, +}; + +FIXTURE_SETUP(omayexec) +{ + /* + * 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=4k")); + + /* Creates a regular file. */ + ASSERT_EQ(0, mknod(reg_file_path, S_IFREG | (variant->file_exec ? 0500 : 0400), 0)); + /* Creates a directory. */ + ASSERT_EQ(0, mkdir(dir_path, variant->file_exec ? 0500 : 0400)); + /* Creates a symlink pointing to the regular file. */ + ASSERT_EQ(0, symlink("regular_file", symlink_path)); + /* 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 | 0400, 0)); + /* Creates a socket. */ + ASSERT_EQ(0, mknod(sock_path, S_IFSOCK | 0400, 0)); + + /* Saves initial sysctl value. */ + self->initial_sysctl_value = sysctl_read_char(_metadata); + + /* Prepares for sysctl writes. */ + ignore_sys_admin(_metadata, 1); +} + +FIXTURE_TEARDOWN(omayexec) +{ + /* Restores initial sysctl value. */ + sysctl_write_char(_metadata, self->initial_sysctl_value); + + /* There is no need to unlink the test files. */ + ASSERT_EQ(0, umount(workdir_path)); + ASSERT_EQ(0, rmdir(workdir_path)); +} + +TEST_F(omayexec, sysctl_0) +{ + /* Do not enforce anything. */ + sysctl_write_char(_metadata, '0'); + test_files(_metadata, 0, false); +} + +TEST_F(omayexec, sysctl_1) +{ + /* Enforces mount exec check. */ + sysctl_write_char(_metadata, '1'); + test_files(_metadata, variant->sysctl_err_code[0], true); +} + +TEST_F(omayexec, sysctl_2) +{ + /* Enforces file exec check. */ + sysctl_write_char(_metadata, '2'); + test_files(_metadata, variant->sysctl_err_code[1], true); +} + +TEST_F(omayexec, sysctl_3) +{ + /* Enforces mount and file exec check. */ + sysctl_write_char(_metadata, '3'); + test_files(_metadata, variant->sysctl_err_code[2], true); +} + +FIXTURE(cleanup) { + char initial_sysctl_value; +}; + +FIXTURE_SETUP(cleanup) +{ + /* Saves initial sysctl value. */ + self->initial_sysctl_value = sysctl_read_char(_metadata); +} + +FIXTURE_TEARDOWN(cleanup) +{ + /* Restores initial sysctl value. */ + ignore_sys_admin(_metadata, 1); + sysctl_write_char(_metadata, self->initial_sysctl_value); +} + +TEST_F(cleanup, sysctl_access_write) +{ + int fd; + ssize_t ret; + + ignore_sys_admin(_metadata, 1); + sysctl_write_char(_metadata, '0'); + + ignore_sys_admin(_metadata, 0); + fd = open(sysctl_path, O_WRONLY | O_CLOEXEC); + ASSERT_LE(0, fd); + ret = write(fd, "0", 1); + ASSERT_EQ(-1, ret); + ASSERT_EQ(EPERM, errno); + EXPECT_EQ(0, close(fd)); +} + +TEST_HARNESS_MAIN From patchwork Thu Jul 23 17:12:27 2020 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: 11681387 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 33883722 for ; Thu, 23 Jul 2020 17:13:55 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 6D47522B40 for ; Thu, 23 Jul 2020 17:13:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6D47522B40 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19433-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 21772 invoked by uid 550); 23 Jul 2020 17:12:57 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 21711 invoked from network); 23 Jul 2020 17:12:56 -0000 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?utf-8?q?Philippe_Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v7 7/7] ima: add policy support for the new file open MAY_OPENEXEC flag Date: Thu, 23 Jul 2020 19:12:27 +0200 Message-Id: <20200723171227.446711-8-mic@digikod.net> X-Mailer: git-send-email 2.28.0.rc1 In-Reply-To: <20200723171227.446711-1-mic@digikod.net> References: <20200723171227.446711-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 From: Mimi Zohar The kernel has no way of differentiating between a file containing data or code being opened by an interpreter. The proposed O_MAYEXEC openat2(2) flag bridges this gap by defining and enabling the MAY_OPENEXEC flag. This patch adds IMA policy support for the new MAY_OPENEXEC flag. Example: measure func=FILE_CHECK mask=^MAY_OPENEXEC appraise func=FILE_CHECK appraise_type=imasig mask=^MAY_OPENEXEC Signed-off-by: Mickaël Salaün Signed-off-by: Mimi Zohar Reviewed-by: Lakshmi Ramasubramanian Link: https://lore.kernel.org/r/1588167523-7866-3-git-send-email-zohar@linux.ibm.com Reviewed-by: Kees Cook --- Documentation/ABI/testing/ima_policy | 2 +- security/integrity/ima/ima_main.c | 3 ++- security/integrity/ima/ima_policy.c | 15 +++++++++++---- 3 files changed, 14 insertions(+), 6 deletions(-) diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index cd572912c593..caca46125fe0 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -31,7 +31,7 @@ Description: [KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK] [KEXEC_CMDLINE] [KEY_CHECK] mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND] - [[^]MAY_EXEC] + [[^]MAY_EXEC] [[^]MAY_OPENEXEC] fsmagic:= hex value fsuuid:= file system UUID (e.g 8bcbe394-4f13-4144-be8e-5aa9ea2ce2f6) uid:= decimal value diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index c1583d98c5e5..59fd1658a203 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -490,7 +490,8 @@ int ima_file_check(struct file *file, int mask) security_task_getsecid(current, &secid); return process_measurement(file, current_cred(), secid, NULL, 0, - mask & (MAY_READ | MAY_WRITE | MAY_EXEC | + mask & (MAY_READ | MAY_WRITE | + MAY_EXEC | MAY_OPENEXEC | MAY_APPEND), FILE_CHECK); } EXPORT_SYMBOL_GPL(ima_file_check); diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index e493063a3c34..6487f0b2afdd 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -406,7 +406,8 @@ static bool ima_match_keyring(struct ima_rule_entry *rule, * @cred: a pointer to a credentials structure for user validation * @secid: the secid of the task to be validated * @func: LIM hook identifier - * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) + * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC | + * MAY_OPENEXEC) * @keyring: keyring name to check in policy for KEY_CHECK func * * Returns true on rule match, false on failure. @@ -527,7 +528,8 @@ static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func) * being made * @secid: LSM secid of the task to be validated * @func: IMA hook identifier - * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) + * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC | + * MAY_OPENEXEC) * @pcr: set the pcr to extend * @template_desc: the template that should be used for this rule * @keyring: the keyring name, if given, to be used to check in the policy. @@ -1091,6 +1093,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) entry->mask = MAY_READ; else if (strcmp(from, "MAY_APPEND") == 0) entry->mask = MAY_APPEND; + else if (strcmp(from, "MAY_OPENEXEC") == 0) + entry->mask = MAY_OPENEXEC; else result = -EINVAL; if (!result) @@ -1422,14 +1426,15 @@ const char *const func_tokens[] = { #ifdef CONFIG_IMA_READ_POLICY enum { - mask_exec = 0, mask_write, mask_read, mask_append + mask_exec = 0, mask_write, mask_read, mask_append, mask_openexec }; static const char *const mask_tokens[] = { "^MAY_EXEC", "^MAY_WRITE", "^MAY_READ", - "^MAY_APPEND" + "^MAY_APPEND", + "^MAY_OPENEXEC" }; void *ima_policy_start(struct seq_file *m, loff_t *pos) @@ -1518,6 +1523,8 @@ int ima_policy_show(struct seq_file *m, void *v) seq_printf(m, pt(Opt_mask), mt(mask_read) + offset); if (entry->mask & MAY_APPEND) seq_printf(m, pt(Opt_mask), mt(mask_append) + offset); + if (entry->mask & MAY_OPENEXEC) + seq_printf(m, pt(Opt_mask), mt(mask_openexec) + offset); seq_puts(m, " "); }