kernel/linux.git/security/landlock, branch v6.1.168

landlock: Add the errata interface

2025-04-25T08:44:02+00:00

commit 15383a0d63dbcd63dc7e8d9ec1bf3a0f7ebf64ac upstream. Some fixes may require user space to check if they are applied on the running kernel before using a specific feature. For instance, this applies when a restriction was previously too restrictive and is now getting relaxed (e.g. for compatibility reasons). However, non-visible changes for legitimate use (e.g. security fixes) do not require an erratum. Because fixes are backported down to a specific Landlock ABI, we need a way to avoid cherry-pick conflicts. The solution is to only update a file related to the lower ABI impacted by this issue. All the ABI files are then used to create a bitmask of fixes. The new errata interface is similar to the one used to get the supported Landlock ABI version, but it returns a bitmask instead because the order of fixes may not match the order of versions, and not all fixes may apply to all versions. The actual errata will come with dedicated commits. The description is not actually used in the code but serves as documentation. Create the landlock_abi_version symbol and use its value to check errata consistency. Update test_base's create_ruleset_checks_ordering tests and add errata tests. This commit is backportable down to the first version of Landlock. Fixes: 3532b0b4352c ("landlock: Enable user space to infer supported features") Cc: Günther Noack Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20250318161443.279194-3-mic@digikod.net Signed-off-by: Mickaël Salaün Signed-off-by: Greg Kroah-Hartman

landlock: Handle weird files

2025-02-21T12:49:04+00:00

[ Upstream commit 49440290a0935f428a1e43a5ac8dc275a647ff80 ] A corrupted filesystem (e.g. bcachefs) might return weird files. Instead of throwing a warning and allowing access to such file, treat them as regular files. Cc: Dave Chinner Cc: Kent Overstreet Cc: Paul Moore Reported-by: syzbot+34b68f850391452207df@syzkaller.appspotmail.com Closes: https://lore.kernel.org/r/000000000000a65b35061cffca61@google.com Reported-by: syzbot+360866a59e3c80510a62@syzkaller.appspotmail.com Closes: https://lore.kernel.org/r/67379b3f.050a0220.85a0.0001.GAE@google.com Reported-by: Ubisectech Sirius Closes: https://lore.kernel.org/r/c426821d-8380-46c4-a494-7008bbd7dd13.bugreport@ubisectech.com Fixes: cb2c7d1a1776 ("landlock: Support filesystem access-control") Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20250110153918.241810-1-mic@digikod.net Signed-off-by: Mickaël Salaün Signed-off-by: Sasha Levin

landlock: Don't lose track of restrictions on cred_transfer

2024-08-03T06:49:29+00:00

commit 39705a6c29f8a2b93cf5b99528a55366c50014d1 upstream. When a process' cred struct is replaced, this _almost_ always invokes the cred_prepare LSM hook; but in one special case (when KEYCTL_SESSION_TO_PARENT updates the parent's credentials), the cred_transfer LSM hook is used instead. Landlock only implements the cred_prepare hook, not cred_transfer, so KEYCTL_SESSION_TO_PARENT causes all information on Landlock restrictions to be lost. This basically means that a process with the ability to use the fork() and keyctl() syscalls can get rid of all Landlock restrictions on itself. Fix it by adding a cred_transfer hook that does the same thing as the existing cred_prepare hook. (Implemented by having hook_cred_prepare() call hook_cred_transfer() so that the two functions are less likely to accidentally diverge in the future.) Cc: stable@kernel.org Fixes: 385975dca53e ("landlock: Set up the security framework and manage credentials") Signed-off-by: Jann Horn Link: https://lore.kernel.org/r/20240724-landlock-houdini-fix-v1-1-df89a4560ca3@google.com Signed-off-by: Mickaël Salaün Signed-off-by: Greg Kroah-Hartman

landlock: Fix d_parent walk

2024-06-21T12:35:43+00:00

commit 88da52ccd66e65f2e63a6c35c9dff55d448ef4dc upstream. The WARN_ON_ONCE() in collect_domain_accesses() can be triggered when trying to link a root mount point. This cannot work in practice because this directory is mounted, but the VFS check is done after the call to security_path_link(). Do not use source directory's d_parent when the source directory is the mount point. Cc: Günther Noack Cc: Paul Moore Cc: stable@vger.kernel.org Reported-by: syzbot+bf4903dc7e12b18ebc87@syzkaller.appspotmail.com Fixes: b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER") Closes: https://lore.kernel.org/r/000000000000553d3f0618198200@google.com Link: https://lore.kernel.org/r/20240516181935.1645983-2-mic@digikod.net [mic: Fix commit message] Signed-off-by: Mickaël Salaün Signed-off-by: Greg Kroah-Hartman

landlock: Warn once if a Landlock action is requested while disabled

2024-04-03T13:19:32+00:00

[ Upstream commit 782191c74875cc33b50263e21d76080b1411884d ] Because sandboxing can be used as an opportunistic security measure, user space may not log unsupported features. Let the system administrator know if an application tries to use Landlock but failed because it isn't enabled at boot time. This may be caused by boot loader configurations with outdated "lsm" kernel's command-line parameter. Cc: stable@vger.kernel.org Fixes: 265885daf3e5 ("landlock: Add syscall implementations") Reviewed-by: Kees Cook Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20240227110550.3702236-2-mic@digikod.net Signed-off-by: Mickaël Salaün Signed-off-by: Sasha Levin

landlock: Fix asymmetric private inodes referring

2024-03-06T14:45:10+00:00

commit d9818b3e906a0ee1ab02ea79e74a2f755fc5461a upstream. When linking or renaming a file, if only one of the source or destination directory is backed by an S_PRIVATE inode, then the related set of layer masks would be used as uninitialized by is_access_to_paths_allowed(). This would result to indeterministic access for one side instead of always being allowed. This bug could only be triggered with a mounted filesystem containing both S_PRIVATE and !S_PRIVATE inodes, which doesn't seem possible. The collect_domain_accesses() calls return early if is_nouser_or_private() returns false, which means that the directory's superblock has SB_NOUSER or its inode has S_PRIVATE. Because rename or link actions are only allowed on the same mounted filesystem, the superblock is always the same for both source and destination directories. However, it might be possible in theory to have an S_PRIVATE parent source inode with an !S_PRIVATE parent destination inode, or vice versa. To make sure this case is not an issue, explicitly initialized both set of layer masks to 0, which means to allow all actions on the related side. If at least on side has !S_PRIVATE, then collect_domain_accesses() and is_access_to_paths_allowed() check for the required access rights. Cc: Arnd Bergmann Cc: Christian Brauner Cc: Günther Noack Cc: Jann Horn Cc: Shervin Oloumi Cc: stable@vger.kernel.org Fixes: b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER") Link: https://lore.kernel.org/r/20240219190345.2928627-1-mic@digikod.net Signed-off-by: Mickaël Salaün Signed-off-by: Greg Kroah-Hartman

landlock: Fix documentation style

2022-09-29T16:43:04+00:00

It seems that all code should use double backquotes, which is also used to convert "%" defines. Let's use an homogeneous style and remove all use of simple backquotes (which should only be used for emphasis). Cc: Günther Noack Cc: Paul Moore Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20220923154207.3311629-4-mic@digikod.net

landlock: Slightly improve documentation and fix spelling

2022-09-29T16:43:03+00:00

Now that we have more than one ABI version, make limitation explanation more consistent by replacing "ABI 1" with "ABI < 2". This also indicates which ABIs support such past limitation. Improve documentation consistency by not using contractions. Fix spelling in fs.c . Cc: Paul Moore Signed-off-by: Mickaël Salaün Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20220923154207.3311629-3-mic@digikod.net

landlock: Fix file reparenting without explicit LANDLOCK_ACCESS_FS_REFER

2022-09-02T13:29:08+00:00

This change fixes a mis-handling of the LANDLOCK_ACCESS_FS_REFER right when multiple rulesets/domains are stacked. The expected behaviour was that an additional ruleset can only restrict the set of permitted operations, but in this particular case, it was potentially possible to re-gain the LANDLOCK_ACCESS_FS_REFER right. With the introduction of LANDLOCK_ACCESS_FS_REFER, we added the first globally denied-by-default access right. Indeed, this lifted an initial Landlock limitation to rename and link files, which was initially always denied when the source or the destination were different directories. This led to an inconsistent backward compatibility behavior which was only taken into account if no domain layer were using the new LANDLOCK_ACCESS_FS_REFER right. However, when restricting a thread with a new ruleset handling LANDLOCK_ACCESS_FS_REFER, all inherited parent rulesets/layers not explicitly handling LANDLOCK_ACCESS_FS_REFER would behave as if they were handling this access right and with all their rules allowing it. This means that renaming and linking files could became allowed by these parent layers, but all the other required accesses must also be granted: all layers must allow file removal or creation, and renaming and linking operations cannot lead to privilege escalation according to the Landlock policy. See detailed explanation in commit b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER"). To say it another way, this bug may lift the renaming and linking limitations of the initial Landlock version, and a same ruleset can enforce different restrictions depending on previous or next enforced ruleset (i.e. inconsistent behavior). The LANDLOCK_ACCESS_FS_REFER right cannot give access to data not already allowed, but this doesn't follow the contract of the first Landlock ABI. This fix puts back the limitation for sandboxes that didn't opt-in for this additional right. For instance, if a first ruleset allows LANDLOCK_ACCESS_FS_MAKE_REG on /dst and LANDLOCK_ACCESS_FS_REMOVE_FILE on /src, renaming /src/file to /dst/file is denied. However, without this fix, stacking a new ruleset which allows LANDLOCK_ACCESS_FS_REFER on / would now permit the sandboxed thread to rename /src/file to /dst/file . This change fixes the (absolute) rule access rights, which now always forbid LANDLOCK_ACCESS_FS_REFER except when it is explicitly allowed when creating a rule. Making all domain handle LANDLOCK_ACCESS_FS_REFER was an initial approach but there is two downsides: * it makes the code more complex because we still want to check that a rule allowing LANDLOCK_ACCESS_FS_REFER is legitimate according to the ruleset's handled access rights (i.e. ABI v1 != ABI v2); * it would not allow to identify if the user created a ruleset explicitly handling LANDLOCK_ACCESS_FS_REFER or not, which will be an issue to audit Landlock. Instead, this change adds an ACCESS_INITIALLY_DENIED list of denied-by-default rights, which (only) contains LANDLOCK_ACCESS_FS_REFER. All domains are treated as if they are also handling this list, but without modifying their fs_access_masks field. A side effect is that the errno code returned by rename(2) or link(2) *may* be changed from EXDEV to EACCES according to the enforced restrictions. Indeed, we now have the mechanic to identify if an access is denied because of a required right (e.g. LANDLOCK_ACCESS_FS_MAKE_REG, LANDLOCK_ACCESS_FS_REMOVE_FILE) or if it is denied because of missing LANDLOCK_ACCESS_FS_REFER rights. This may result in different errno codes than for the initial Landlock version, but this approach is more consistent and better for rename/link compatibility reasons, and it wasn't possible before (hence no backport to ABI v1). The layout1.rename_file test reflects this change. Add 4 layout1.refer_denied_by_default* test suites to check that the behavior of a ruleset not handling LANDLOCK_ACCESS_FS_REFER (ABI v1) is unchanged even if another layer handles LANDLOCK_ACCESS_FS_REFER (i.e. ABI v1 precedence). Make sure rule's absolute access rights are correct by testing with and without a matching path. Add test_rename() and test_exchange() helpers. Extend layout1.inval tests to check that a denied-by-default access right is not necessarily part of a domain's handled access rights. Test coverage for security/landlock is 95.3% of 599 lines according to gcc/gcov-11. Fixes: b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER") Reviewed-by: Paul Moore Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20220831203840.1370732-1-mic@digikod.net Cc: stable@vger.kernel.org [mic: Constify and slightly simplify test helpers] Signed-off-by: Mickaël Salaün

landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER

2022-05-23T11:27:59+00:00

Add a new LANDLOCK_ACCESS_FS_REFER access right to enable policy writers to allow sandboxed processes to link and rename files from and to a specific set of file hierarchies. This access right should be composed with LANDLOCK_ACCESS_FS_MAKE_* for the destination of a link or rename, and with LANDLOCK_ACCESS_FS_REMOVE_* for a source of a rename. This lift a Landlock limitation that always denied changing the parent of an inode. Renaming or linking to the same directory is still always allowed, whatever LANDLOCK_ACCESS_FS_REFER is used or not, because it is not considered a threat to user data. However, creating multiple links or renaming to a different parent directory may lead to privilege escalations if not handled properly. Indeed, we must be sure that the source doesn't gain more privileges by being accessible from the destination. This is handled by making sure that the source hierarchy (including the referenced file or directory itself) restricts at least as much the destination hierarchy. If it is not the case, an EXDEV error is returned, making it potentially possible for user space to copy the file hierarchy instead of moving or linking it. Instead of creating different access rights for the source and the destination, we choose to make it simple and consistent for users. Indeed, considering the previous constraint, it would be weird to require such destination access right to be also granted to the source (to make it a superset). Moreover, RENAME_EXCHANGE would also add to the confusion because of paths being both a source and a destination. See the provided documentation for additional details. New tests are provided with a following commit. Reviewed-by: Paul Moore Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20220506161102.525323-8-mic@digikod.net