From: "Mickaël Salaün" <email@example.com> To: James Morris <firstname.lastname@example.org>, "Serge E . Hallyn" <email@example.com> Cc: "Mickaël Salaün" <firstname.lastname@example.org>, "Al Viro" <email@example.com>, "Jann Horn" <firstname.lastname@example.org>, "John Johansen" <email@example.com>, "Kees Cook" <firstname.lastname@example.org>, "Konstantin Meskhidze" <email@example.com>, "Paul Moore" <firstname.lastname@example.org>, "Shuah Khan" <email@example.com>, "Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: [PATCH v3 00/12] Landlock: file linking and renaming support Date: Fri, 6 May 2022 18:10:50 +0200 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) Hi, This third patch series is mostly a rebase with some whitespace changes because of clang-format. There is also some new "unlikely()" calls and minor code cleanup. Test coverage for security/landlock was 94.4% of 504 lines (with the previous patch series), and it is now 95.4% of 604 lines according to gcc/gcov-11. Problem ======= One of the most annoying limitations of Landlock is that sandboxed processes can only link and rename files to the same directory (i.e. file reparenting is always denied). Indeed, because of the unprivileged nature of Landlock, file hierarchy are identified thanks to ephemeral inode tagging, which may cause arbitrary renaming and linking to change the security policy in an unexpected way. Solution ======== This patch series brings a new access right, LANDLOCK_ACCESS_FS_REFER, which enables to allow safe file linking and renaming. In a nutshell, Landlock checks that the inherited access rights of a moved or renamed file cannot increase but only reduce. Eleven new test suits cover file renaming and linking, which improves test coverage. The documentation and the tutorial is extended with this new access right, along with more explanations about backward and forward compatibility, good practices, and a bit about the current access rights rational. While developing this new feature, I also found an issue with the current implementation of Landlock. In some (rare) cases, sandboxed processes may be more restricted than intended. Indeed, because of the current way to check file hierarchy access rights, composition of rules may be incomplete when requesting multiple accesses at the same time. This is fixed with a dedicated patch involving some refactoring. A new test suite checks relevant new edge cases. As a side effect, and to limit the increased use of the stack, I reduced the number of Landlock nested domains from 64 to 16. I think this should be more than enough for legitimate use cases, but feel free to challenge this decision with real and legitimate use cases. Additionally, a new dedicated syzkaller test has been developed to cover new paths. This patch series is based on and was developed with some complementary new tests sent in a standalone patch series: https://email@example.com Previous versions: v2: https://firstname.lastname@example.org v1: https://email@example.com Regards, Mickaël Salaün (12): landlock: Define access_mask_t to enforce a consistent access mask size landlock: Reduce the maximum number of layers to 16 landlock: Create find_rule() from unmask_layers() landlock: Fix same-layer rule unions landlock: Move filesystem helpers and add a new one LSM: Remove double path_rename hook calls for RENAME_EXCHANGE landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER selftests/landlock: Add 11 new test suites dedicated to file reparenting samples/landlock: Add support for file reparenting landlock: Document LANDLOCK_ACCESS_FS_REFER and ABI versioning landlock: Document good practices about filesystem policies landlock: Add design choices documentation for filesystem access rights Documentation/security/landlock.rst | 17 +- Documentation/userspace-api/landlock.rst | 151 ++- include/linux/lsm_hook_defs.h | 2 +- include/linux/lsm_hooks.h | 1 + include/uapi/linux/landlock.h | 27 +- samples/landlock/sandboxer.c | 40 +- security/apparmor/lsm.c | 30 +- security/landlock/fs.c | 771 ++++++++++--- security/landlock/fs.h | 2 +- security/landlock/limits.h | 6 +- security/landlock/ruleset.c | 6 +- security/landlock/ruleset.h | 22 +- security/landlock/syscalls.c | 2 +- security/security.c | 9 +- security/tomoyo/tomoyo.c | 11 +- tools/testing/selftests/landlock/base_test.c | 2 +- tools/testing/selftests/landlock/fs_test.c | 1039 ++++++++++++++++-- 17 files changed, 1853 insertions(+), 285 deletions(-) base-commit: 4b0cdb0cf6eefa7521322007931ccfb7edc96c53 -- 2.35.1
next reply other threads:[~2022-05-06 16:11 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-05-06 16:10 Mickaël Salaün [this message] 2022-05-06 16:10 ` [PATCH v3 01/12] landlock: Define access_mask_t to enforce a consistent access mask size Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 02/12] landlock: Reduce the maximum number of layers to 16 Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 03/12] landlock: Create find_rule() from unmask_layers() Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 04/12] landlock: Fix same-layer rule unions Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 05/12] landlock: Move filesystem helpers and add a new one Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 06/12] LSM: Remove double path_rename hook calls for RENAME_EXCHANGE Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 07/12] landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 08/12] selftests/landlock: Add 11 new test suites dedicated to file reparenting Mickaël Salaün 2022-05-06 16:10 ` [PATCH v3 09/12] samples/landlock: Add support for " Mickaël Salaün 2022-05-06 16:11 ` [PATCH v3 10/12] landlock: Document LANDLOCK_ACCESS_FS_REFER and ABI versioning Mickaël Salaün 2022-05-06 16:11 ` [PATCH v3 11/12] landlock: Document good practices about filesystem policies Mickaël Salaün 2022-05-06 16:11 ` [PATCH v3 12/12] landlock: Add design choices documentation for filesystem access rights Mickaël Salaün 2022-05-06 16:31 ` [PATCH v3 00/12] Landlock: file linking and renaming support Mickaël Salaün
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