From patchwork Wed Nov 23 15:47:06 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Roberto Sassu X-Patchwork-Id: 13053894 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7FF84C4167D for ; Wed, 23 Nov 2022 15:48:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238048AbiKWPsN (ORCPT ); Wed, 23 Nov 2022 10:48:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37512 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238723AbiKWPsK (ORCPT ); Wed, 23 Nov 2022 10:48:10 -0500 Received: from frasgout13.his.huawei.com (frasgout13.his.huawei.com [14.137.139.46]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6213A1B5; Wed, 23 Nov 2022 07:48:07 -0800 (PST) Received: from mail02.huawei.com (unknown [172.18.147.229]) by frasgout13.his.huawei.com (SkyGuard) with ESMTP id 4NHQMY4q3Rz9xGKG; Wed, 23 Nov 2022 23:41:13 +0800 (CST) Received: from huaweicloud.com (unknown [10.204.63.22]) by APP1 (Coremail) with SMTP id LxC2BwD34W6OQH5jUE+LAA--.33660S2; Wed, 23 Nov 2022 16:47:38 +0100 (CET) From: Roberto Sassu To: mark@fasheh.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com, zohar@linux.ibm.com, dmitry.kasatkin@gmail.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, stephen.smalley.work@gmail.com, eparis@parisplace.org, casey@schaufler-ca.com Cc: ocfs2-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-kernel@vger.kernel.org, keescook@chromium.org, nicolas.bouchinet@clip-os.org, Roberto Sassu Subject: [PATCH v6 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes Date: Wed, 23 Nov 2022 16:47:06 +0100 Message-Id: <20221123154712.752074-1-roberto.sassu@huaweicloud.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-CM-TRANSID: LxC2BwD34W6OQH5jUE+LAA--.33660S2 X-Coremail-Antispam: 1UD129KBjvJXoWxKFy3Xr47Aw1rKry3XFy8uFg_yoWfKr4xpF Wjg3W5Krn8AFWjgrWfAa1xua1SgrWrGr47Jrs3Gryjy3Z8Gr1xtr1Ikry5ua45XrZ5AF9a qw17Awn8u3Z8A37anT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkIb4IE77IF4wAFF20E14v26ryj6rWUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Jr0_JF4l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr0_Cr1l84ACjcxK6I8E87Iv67AKxVW8JVWxJwA2z4x0Y4vEx4A2jsIEc7CjxV AFwI0_Gr1j6F4UJwAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcxkI7VAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7MxAIw28I cxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr4lx2 IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVW8ZVWrXwCIc40Y0x0EwIxGrwCI 42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwCI42 IY6xAIw20EY4v20xvaj40_WFyUJVCq3wCI42IY6I8E87Iv67AKxVW8JVWxJwCI42IY6I8E 87Iv6xkF7I0E14v26r4UJVWxJrUvcSsGvfC2KfnxnUUI43ZEXa7IU13rcDUUUUU== X-CM-SenderInfo: purev21wro2thvvxqx5xdzvxpfor3voofrz/1tbiAgAFBF1jj4HL3wABsm X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org From: Roberto Sassu One of the major goals of LSM stacking is to run multiple LSMs side by side without interfering with each other. The ultimate decision will depend on individual LSM decision. Several changes need to be made to the LSM infrastructure to be able to support that. This patch set tackles one of them: gives to each LSM the ability to specify one or multiple xattrs to be set at inode creation time and, at the same time, gives to EVM the ability to access all those xattrs and calculate the HMAC on them. The first problem that this patch set addresses is to make the inode_init_security hook definition suitable to use with EVM which, unlike other LSMs, needs to have visibility of all xattrs and not only the one that the LSM infrastructure passes to the LSM to be set. The solution is to replace in the inode_init_security definition the name/value/len parameters with the beginning of the array containing all xattrs set by LSMs. Due to security_old_inode_init_security() API limitation of setting only one xattr, it has been dropped and the remaining users, ocfs2 and reiserfs, switch to security_inode_init_security(). However, due to the complexity of the changes required to fully exploit the ability of security_inode_init_security() to set multiple xattrs, those users can still set only one xattr (the first set in the xattr array) where previously they called security_old_inode_init_security(). Furthermore, while EVM is invoked unlike before, its xattr will not be set as it would not be the first set in the xattr array, or if it is the first, there would not be protected xattrs to calculate the HMAC on. The second problem this patch set addresses is the limitation of the call_int_hook() of stopping the loop when the return value from a hook implementation is not zero. Unfortunately, for the inode_init_security hook it is a legitimate case to return -EOPNOTSUPP, but this would not necessarily mean that there is an error to report to the LSM infrastructure but just that an LSM does not will to set an xattr. Other LSMs should be still consulted as well. The solution for this specific case is to replace the call_int_hook() with the loop itself, so that -EOPNOTSUPP can be ignored. Next, this patch set removes the limitation of creating only two xattrs, one by an active LSM and another by EVM. This patch set extends the reservation mechanism of the LSM infrastructure, to allow each LSM to request one or multiple xattrs. While this could potentially lead to reaching the filesystem limits of number/size of the xattrs, it seems not an issue that need to be solved by the LSM infrastructure but by the filesystems themselves. Currently, if the limit is reached, the only workaround would be to use fewer LSMs. The reservation mechanism concept makes it very easy for LSMs to position themselves correctly in the xattr array, as the LSM infrastructure at initialization time changes the number of xattrs requested by each LSM with an offset. LSMs can just take that offset as the starting index in the xattr array and fill the next slots depending on how many xattrs they requested. However, while this concept is intuitive, it needs extra care. While for security blobs (the main reason of the reservation mechanism) it is not relevant for an LSM if other LSMs filled their portion, it matters for xattrs, as both EVM and initxattrs() callbacks scan the entire array until a terminator (xattr with NULL name). If an LSM did not provide an xattr, which could happen if it is loaded but not initialized, consumers of the xattr array would stop prematurely. This patch set avoids this problem by compacting the xattr array each time after an LSM executed its implementation of the inode_init_security hook. It needs to be done after each LSM, and not after all, since there might be LSMs scanning that xattr array too. Compacting the array after all LSMs would be too late. Finally, this patch set modifies the evm_inode_init_security() definition to be compatible with the inode_init_security hook definition and adds support for scanning the whole xattr array and for calculating the HMAC on all xattrs provided by LSMs. This patch set has been tested by introducing several instances of a TestLSM (some providing an xattr, some not, one with a wrong implementation to see how the LSM infrastructure handles it, one providing multiple xattrs and another providing an xattr but in a disabled state). The patch is not included in this set but it is available here: https://github.com/robertosassu/linux/commit/e13a03236df0c399dccb73df5fe4cfceb4bb1d89 The test, added to ima-evm-utils, is available here: https://github.com/robertosassu/ima-evm-utils/blob/evm-multiple-lsms-v5-devel-v3/tests/evm_multiple_lsms.test The test takes a UML kernel built by Github Actions and launches it several times, each time with a different combination of LSMs and filesystems (ext4, reiserfs, ocfs2). After boot, it first checks that there is an xattr for each LSM providing it (for reiserfs and ocfs2 just the first LSM), and then (for ext4) calculates the HMAC in user space and compares it with the HMAC calculated by EVM in kernel space. A test report can be obtained here: https://github.com/robertosassu/ima-evm-utils/actions/runs/3525619568/jobs/5912560168 The patch set has been tested with both the SElinux and Smack test suites. Below, there is the summary of the test results: SELinux Test Suite result (without patches): Files=73, Tests=1346, 225 wallclock secs ( 0.43 usr 0.23 sys + 6.11 cusr 58.70 csys = 65.47 CPU) Result: FAIL Failed 4/73 test programs. 13/1346 subtests failed. SELinux Test Suite result (with patches): Files=73, Tests=1346, 225 wallclock secs ( 0.44 usr 0.22 sys + 6.15 cusr 59.94 csys = 66.75 CPU) Result: FAIL Failed 4/73 test programs. 13/1346 subtests failed. Smack Test Suite result (without patches): 95 Passed, 0 Failed, 100% Success rate Smack Test Suite result (with patches): 95 Passed, 0 Failed, 100% Success rate Changelog v5: - Modify the cover letter to explain that the goal of this patch set is supporting multiple per LSM xattrs in EVM, and not moving IMA and EVM to the LSM infrastructure - Remove references in the patches description about moving IMA and EVM to the LSM infrastructure - Explain that the additional EVM invocation due to the switch to security_inode_init_security() will not cause the EVM xattr to be added v4: - Remove patch to call reiserfs_security_free(), already queued - Switch ocfs2 and reiserfs to security_inode_init_security() (suggested by Mimi) - Remove security_old_inode_init_security() (suggested by Paul) - Rename security_check_compact_xattrs() to security_check_compact_filled_xattrs() and add function description (suggested by Mimi) - Rename checked_xattrs parameter of security_check_compact_filled_xattrs() to num_filled_xattrs (suggested by Mimi) - Rename cur_xattrs variable in security_inode_init_security() to num_filled_xattrs (suggested by Mimi) v3: - Don't free the xattr name in reiserfs_security_free() - Don't include fs_data parameter in inode_init_security hook - Don't change evm_inode_init_security(), as it will be removed if EVM is stacked - Fix inode_init_security hook documentation - Drop lsm_find_xattr_slot(), use simple xattr reservation mechanism and introduce security_check_compact_xattrs() to compact the xattr array - Don't allocate xattr array if LSMs didn't reserve any xattr - Return zero if initxattrs() is not provided to security_inode_init_security(), -EOPNOTSUPP if value is not provided to security_old_inode_init_security() - Request LSMs to fill xattrs if only value (not the triple) is provided to security_old_inode_init_security(), to avoid unnecessary memory allocation v2: - rewrite selinux_old_inode_init_security() to use security_inode_init_security() - add lbs_xattr field to lsm_blob_sizes structure, to give the ability to LSMs to reserve slots in the xattr array (suggested by Casey) - add new parameter base_slot to inode_init_security hook definition v1: - add calls to reiserfs_security_free() and initialize sec->value to NULL (suggested by Tetsuo and Mimi) - change definition of inode_init_security hook, replace the name, value and len triple with the xattr array (suggested by Casey) - introduce lsm_find_xattr_slot() helper for LSMs to find an unused slot in the passed xattr array Roberto Sassu (6): reiserfs: Switch to security_inode_init_security() ocfs2: Switch to security_inode_init_security() security: Remove security_old_inode_init_security() security: Allow all LSMs to provide xattrs for inode_init_security hook evm: Align evm_inode_init_security() definition with LSM infrastructure evm: Support multiple LSMs providing an xattr fs/ocfs2/namei.c | 18 ++--- fs/ocfs2/xattr.c | 30 +++++++- fs/reiserfs/xattr_security.c | 23 ++++-- include/linux/evm.h | 12 +-- include/linux/lsm_hook_defs.h | 3 +- include/linux/lsm_hooks.h | 17 ++-- include/linux/security.h | 12 --- security/integrity/evm/evm.h | 2 + security/integrity/evm/evm_crypto.c | 9 ++- security/integrity/evm/evm_main.c | 28 +++++-- security/security.c | 115 +++++++++++++++++++++------- security/selinux/hooks.c | 19 +++-- security/smack/smack_lsm.c | 26 ++++--- 13 files changed, 213 insertions(+), 101 deletions(-) Reviewed-by: Casey Schaufler