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 <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
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 <mic@digikod.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Use landlock_cred(file->f_cred)->domain instead of
landlock_get_current_domain() in security_file_open() hook
implementation.

This should not change the current behavior but could avoid potential
race conditions in case of current task's credentials change.

This will also ensure consistency with upcoming audit support relying on
file->f_cred.

Add and use a new get_fs_domain() helper to mask non-filesystem domains.

file->f_cred is set by path_openat()/alloc_empty_file()/init_file() just
before calling security_file_alloc().

Cc: Christian Brauner <brauner@kernel.org>
Cc: Günther Noack <gnoack@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240307095203.1467189-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

ptrace.[ch] are currently only used for the ptrace LSM hooks but their
scope will expand with IPCs and audit support.  Rename ptrace.[ch] to
task.[ch], which better reflect their content.  Similarly, rename
landlock_add_ptrace_hooks() to landlock_add_task_hooks().  Keep header
files for now.

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20240307093923.1466071-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Remove the handled_access variable in current_check_access_socket() and
update access_request instead.  One up-to-date variable avoids picking
the wrong one.

Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Link: https://lore.kernel.org/r/20240307093923.1466071-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

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 <keescook@chromium.org>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20240227110550.3702236-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Add the SECURITY_LANDLOCK_KUNIT_TEST option to enable KUnit tests for
Landlock.  The minimal required configuration is listed in the
security/landlock/.kunitconfig file.

Add an initial landlock_fs KUnit test suite with 7 test cases for
filesystem helpers.  These are related to the LANDLOCK_ACCESS_FS_REFER
right.

There is one KUnit test case per:
* mutated state (e.g. test_scope_to_request_*) or,
* shared state between tests (e.g. test_is_eaccess_*).

Add macros to improve readability of tests (i.e. one per line).  Test
cases are collocated with the tested functions to help maintenance and
improve documentation.  This is why SECURITY_LANDLOCK_KUNIT_TEST cannot
be set as module.

This is a nice complement to Landlock's user space kselftests.  We
expect new Landlock features to come with KUnit tests as well.

Thanks to UML support, we can run all KUnit tests for Landlock with:
./tools/testing/kunit/kunit.py run --kunitconfig security/landlock

[00:00:00] ======================= landlock_fs  =======================
[00:00:00] [PASSED] test_no_more_access
[00:00:00] [PASSED] test_scope_to_request_with_exec_none
[00:00:00] [PASSED] test_scope_to_request_with_exec_some
[00:00:00] [PASSED] test_scope_to_request_without_access
[00:00:00] [PASSED] test_is_eacces_with_none
[00:00:00] [PASSED] test_is_eacces_with_refer
[00:00:00] [PASSED] test_is_eacces_with_write
[00:00:00] =================== [PASSED] landlock_fs ===================
[00:00:00] ============================================================
[00:00:00] Testing complete. Ran 7 tests: passed: 7

Cc: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Reviewed-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20240118113632.1948478-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

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 <arnd@arndb.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Günther Noack <gnoack@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Shervin Oloumi <enlightened@chromium.org>
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 <mic@digikod.net>

Pull Landlock updates from Mickaël Salaün:
 "New tests, a slight optimization, and some cosmetic changes"

* tag 'landlock-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux:
  landlock: Optimize the number of calls to get_access_mask slightly
  selftests/landlock: Rename "permitted" to "allowed" in ftruncate tests
  landlock: Remove remaining "inline" modifiers in .c files [v6.6]
  landlock: Remove remaining "inline" modifiers in .c files [v6.1]
  landlock: Remove remaining "inline" modifiers in .c files [v5.15]
  selftests/landlock: Add tests to check unhandled rule's access rights
  selftests/landlock: Add tests to check unknown rule's access rights

This call is now going through a function pointer,
and it is not as obvious any more that it will be inlined.

Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20231208155121.1943775-4-gnoack@google.com
Fixes: 7a11275c3787 ("landlock: Refactor layer helpers")
Signed-off-by: Mickaël Salaün <mic@digikod.net>

For module-internal static functions, compilers are already in a good
position to decide whether to inline them or not.

Suggested-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20231208155121.1943775-2-gnoack@google.com
[mic: Split patch for Linux 6.6]
Signed-off-by: Mickaël Salaün <mic@digikod.net>