From patchwork Wed May 9 20:28:11 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Garrett X-Patchwork-Id: 10390809 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id AA59E60236 for ; Wed, 9 May 2018 20:28:25 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3779128334 for ; Wed, 9 May 2018 20:28:21 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 2C3BD285D1; Wed, 9 May 2018 20:28:21 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, USER_IN_DEF_DKIM_WL autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6205328334 for ; Wed, 9 May 2018 20:28:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756254AbeEIU2U (ORCPT ); Wed, 9 May 2018 16:28:20 -0400 Received: from mail-yb0-f202.google.com ([209.85.213.202]:47224 "EHLO mail-yb0-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751756AbeEIU2T (ORCPT ); Wed, 9 May 2018 16:28:19 -0400 Received: by mail-yb0-f202.google.com with SMTP id l7-v6so23962754ybk.14 for ; Wed, 09 May 2018 13:28:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:date:in-reply-to:message-id:references:subject:from:to :cc; bh=2CtTGKBqsTryhv3i7KwRgeZsHb0Tfd8QREhtozmGbww=; b=bJ9NxoUSpDi6SESpnuSC8i2l6/pKeAiIAxwTQGSP7lfnbOC4G+ftE590T3kfroqb7f Ud5O88bQ7dvAc5Z+YW+qhe6tlcfl86h61zu7EVfrAAjfCON21wvojsjNGkO9rav3qFMD bWCD5uPclkHbwvV09OXbCygo2acVX2PEgoAx5y+eRtF8HTJZ/F04p+9XWklfHM8ZKlL2 kO71zXh/MFYNi6erPHKmwOdvqXY2/PiBztyDxuqB3oG0/ZvNDXGquCjRVeX9Icru/L7w A093hluoN16G0XY8qgBlyBbq1Mi0Vc+0LdDM2kEoIamOCOlnCYHShsF2ddEIewFe4Jqc AB2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:date:in-reply-to:message-id :references:subject:from:to:cc; bh=2CtTGKBqsTryhv3i7KwRgeZsHb0Tfd8QREhtozmGbww=; b=jvWfXIFBBE+1OUt/3ExqSP1j1fS2vBlIsHS1d5s4zB1p9X1MMHUfwZgbyVuP5ZF2rR Co4esi5frxWvmh5vRwzT8ij1fBgqkLDnI/fUhzm5HBWFGxQm796CGJIGZchutFX/5ky6 zLfD88ug3oxqiunA13CK72SpNd/Xu+PbEIW1yIjHRcXSycZrWJRO6hnTf6PE8rh1zjO4 +ueJrJV07UkHnar28f+pFgdQVU+I9dPJ+g+jR6yraPzFjmSQB4Xgo+QR0j23/yZMEH9y KMYVDO2FRUMUIeOLmomQavLDD63xfa8OwwqAKK/wC0CM+0cbE7sqJw//GUqPGHBN7P3n JXAQ== X-Gm-Message-State: ALQs6tBeNFY7v+r+6HXvOLbojqv7tIW/x9OujYz9mZXIPW0cAJ3WNv/4 GABSwpk6oZJNVjtmncT1QjHc0VXRx/Ji6+47VpqihM5HhgkvV0lejv5LT5oHBKZRjUVySPMnqdO O+YuAvenK+TZ2cVtGlgggDrRrBvi6z9rg/tU= X-Google-Smtp-Source: AB8JxZog6iMB4ICMSmakPAHWnqe6eQzj8LvdwOoKK7hNOvJ3FzG05i87daqKfpEcHbnJSqlkoMADNNhiw/RzUHsTkVkotA== MIME-Version: 1.0 X-Received: by 2002:a25:5f0e:: with SMTP id t14-v6mr15965098ybb.60.1525897698615; Wed, 09 May 2018 13:28:18 -0700 (PDT) Date: Wed, 9 May 2018 13:28:11 -0700 In-Reply-To: <20180509202811.29875-1-mjg59@google.com> Message-Id: <20180509202811.29875-2-mjg59@google.com> References: <20180509202811.29875-1-mjg59@google.com> X-Mailer: git-send-email 2.17.0.441.gb46fe60e1d-goog Subject: [PATCH V4 2/2] EVM: Allow runtime modification of the set of verified xattrs From: Matthew Garrett To: linux-integrity@vger.kernel.org Cc: zohar@linux.vnet.ibm.com, Matthew Garrett Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Sites may wish to provide additional metadata alongside files in order to make more fine-grained security decisions[1]. The security of this is enhanced if this metadata is protected, something that EVM makes possible. However, the kernel cannot know about the set of extended attributes that local admins may wish to protect, and hardcoding this policy in the kernel makes it difficult to change over time and less convenient for distributions to enable. This patch adds a new /sys/kernel/security/evm_xattrs node, which can be read to obtain the current set of EVM-protected extended attributes or written to in order to add new entries. Extending this list will not change the validity of any existing signatures provided that the file in question does not have any of the additional extended attributes - missing xattrs are skipped when calculating the EVM hash. [1] For instance, a package manager could install information about the package uploader in an additional extended attribute. Local LSM policy could then be associated with that extended attribute in order to restrict the privileges available to packages from less trusted uploaders. Signed-off-by: Matthew Garrett Reviewed-by: James Morris --- Updated to add support for locking down the list, and also to forbid adding the same xattr twice. Documentation/ABI/testing/evm | 13 +++ security/integrity/evm/Kconfig | 11 ++ security/integrity/evm/evm_crypto.c | 2 +- security/integrity/evm/evm_main.c | 6 +- security/integrity/evm/evm_secfs.c | 153 ++++++++++++++++++++++++++-- 5 files changed, 175 insertions(+), 10 deletions(-) diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm index d12cb2eae9ee..fa31df7fd30b 100644 --- a/Documentation/ABI/testing/evm +++ b/Documentation/ABI/testing/evm @@ -57,3 +57,16 @@ Description: dracut (via 97masterkey and 98integrity) and systemd (via core/ima-setup) have support for loading keys at boot time. + +What: security/evm_xattrs +Date: April 2018 +Contact: Matthew Garrett +Description: + Shows the set of extended attributes used to calculate or + validate the EVM signature, and allows additional attributes + to be added at runtime. Any signatures generated after + additional attributes are added (and on files posessing those + additional attributes) will only be valid if the same + additional attributes are configured on system boot. Writing + a single period (.) will lock the xattr list from any further + modification. diff --git a/security/integrity/evm/Kconfig b/security/integrity/evm/Kconfig index e825e0ae78e7..54adb3f9ad1d 100644 --- a/security/integrity/evm/Kconfig +++ b/security/integrity/evm/Kconfig @@ -42,6 +42,17 @@ config EVM_EXTRA_SMACK_XATTRS additional info to the calculation, requires existing EVM labeled file systems to be relabeled. +config EVM_ADD_XATTRS + bool "Add additional EVM extended attributes at runtime" + depends on EVM + default n + help + Allow userland to provide additional xattrs for HMAC calculation. + + When this option is enabled, root can add additional xattrs to the + list used by EVM by writing them into + /sys/kernel/security/evm_xattrs. + config EVM_LOAD_X509 bool "Load an X509 certificate onto the '.evm' trusted keyring" depends on EVM && INTEGRITY_TRUSTED_KEYRING diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c index caeea20670cc..494da5fcc092 100644 --- a/security/integrity/evm/evm_crypto.c +++ b/security/integrity/evm/evm_crypto.c @@ -208,7 +208,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry, return PTR_ERR(desc); error = -ENODATA; - list_for_each_entry(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { bool is_ima = false; if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index dd2415c55982..f049af2cc037 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -35,7 +35,7 @@ static const char * const integrity_status_msg[] = { }; int evm_hmac_attrs; -static struct xattr_list evm_config_default_xattrnames[] __ro_after_init = { +static struct xattr_list evm_config_default_xattrnames[] = { #ifdef CONFIG_SECURITY_SELINUX {.name = XATTR_NAME_SELINUX}, #endif @@ -98,7 +98,7 @@ static int evm_find_protected_xattrs(struct dentry *dentry) if (!(inode->i_opflags & IOP_XATTR)) return -EOPNOTSUPP; - list_for_each_entry(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0); if (error < 0) { if (error == -ENODATA) @@ -225,7 +225,7 @@ static int evm_protected_xattr(const char *req_xattr_name) struct xattr_list *xattr; namelen = strlen(req_xattr_name); - list_for_each_entry(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { if ((strlen(xattr->name) == namelen) && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) { found = 1; diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c index feba03bbedae..8dc11c0ac8a0 100644 --- a/security/integrity/evm/evm_secfs.c +++ b/security/integrity/evm/evm_secfs.c @@ -17,10 +17,17 @@ #include #include +#include #include "evm.h" static struct dentry *evm_init_tpm; +#ifdef CONFIG_EVM_ADD_XATTRS +static struct dentry *evm_xattrs; +static DEFINE_MUTEX(xattr_list_mutex); +static int evm_xattrs_locked; +#endif + /** * evm_read_key - read() for /evm * @@ -107,13 +114,147 @@ static const struct file_operations evm_key_ops = { .write = evm_write_key, }; -int __init evm_init_secfs(void) +#ifdef CONFIG_EVM_ADD_XATTRS +/** + * evm_read_xattrs - read() for /evm_xattrs + * + * @filp: file pointer, not actually used + * @buf: where to put the result + * @count: maximum to send along + * @ppos: where to start + * + * Returns number of bytes read or error code, as appropriate + */ +static ssize_t evm_read_xattrs(struct file *filp, char __user *buf, + size_t count, loff_t *ppos) +{ + char *temp; + int offset = 0; + ssize_t rc, size = 0; + struct xattr_list *xattr; + + if (*ppos != 0) + return 0; + + rc = mutex_lock_interruptible(&xattr_list_mutex); + if (rc) + return -ERESTARTSYS; + + list_for_each_entry(xattr, &evm_config_xattrnames, list) + size += strlen(xattr->name) + 1; + + temp = kmalloc(size + 1, GFP_KERNEL); + if (!temp) + return -ENOMEM; + + list_for_each_entry(xattr, &evm_config_xattrnames, list) { + sprintf(temp + offset, "%s\n", xattr->name); + offset += strlen(xattr->name) + 1; + } + + mutex_unlock(&xattr_list_mutex); + rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp)); + + return rc; +} + +/** + * evm_write_xattrs - write() for /evm_xattrs + * @file: file pointer, not actually used + * @buf: where to get the data from + * @count: bytes sent + * @ppos: where to start + * + * Returns number of bytes written or error code, as appropriate + */ +static ssize_t evm_write_xattrs(struct file *file, const char __user *buf, + size_t count, loff_t *ppos) +{ + int len, err; + struct xattr_list *xattr, *tmp; + + if (!capable(CAP_SYS_ADMIN) || evm_xattrs_locked) + return -EPERM; + + if (*ppos != 0) + return -EINVAL; + + if (count > XATTR_NAME_MAX) + return -E2BIG; + + xattr = kmalloc(sizeof(struct xattr_list), GFP_KERNEL); + if (!xattr) + return -ENOMEM; + + xattr->name = memdup_user_nul(buf, count); + if (IS_ERR(xattr->name)) { + err = PTR_ERR(xattr->name); + kfree(xattr); + return err; + } + + /* Remove any trailing newline */ + len = strlen(xattr->name); + if (xattr->name[len-1] == '\n') + xattr->name[len-1] = '\0'; + + if (strcmp(xattr->name, ".") == 0) { + evm_xattrs_locked = 1; + err = count; + goto out; + } + + /* Guard against races in evm_read_xattrs */ + mutex_lock(&xattr_list_mutex); + list_for_each_entry(tmp, &evm_config_xattrnames, list) { + if (strcmp(xattr->name, tmp->name) == 0) { + err = -EEXIST; + mutex_unlock(&xattr_list_mutex); + goto out; + } + } + list_add_tail_rcu(&xattr->list, &evm_config_xattrnames); + mutex_unlock(&xattr_list_mutex); + + return count; +out: + kfree(xattr->name); + kfree(xattr); + return err; +} + +static const struct file_operations evm_xattr_ops = { + .read = evm_read_xattrs, + .write = evm_write_xattrs, +}; + +static int evm_init_xattrs(void) +{ + evm_xattrs = securityfs_create_file("evm_xattrs", 0440, NULL, NULL, + &evm_xattr_ops); + if (!evm_xattrs || IS_ERR(evm_xattrs)) + return -EFAULT; + + return 0; +} +#else +static int evm_init_xattrs(void) { - int error = 0; + return 0; +} +#endif - evm_init_tpm = securityfs_create_file("evm", S_IRUSR | S_IRGRP, - NULL, NULL, &evm_key_ops); +int __init evm_init_secfs(void) +{ + evm_init_tpm = securityfs_create_file("evm", 0440, NULL, NULL, + &evm_key_ops); if (!evm_init_tpm || IS_ERR(evm_init_tpm)) - error = -EFAULT; - return error; + return -EFAULT; + + if (evm_init_xattrs()) { + securityfs_remove(evm_init_tpm); + return -EFAULT; + } + + return 0; }