landlock: Log truncate and IOCTL denials

Add audit support to the file_truncate and file_ioctl hooks.

Add a deny_masks_t type and related helpers to store the domain's layer
level per optional access rights (i.e. LANDLOCK_ACCESS_FS_TRUNCATE and
LANDLOCK_ACCESS_FS_IOCTL_DEV) when opening a file, which cannot be
inferred later.  In practice, the landlock_file_security aligned blob size is
still 16 bytes because this new one-byte deny_masks field follows the
existing two-bytes allowed_access field and precede the packed
fown_subject.

Implementing deny_masks_t with a bitfield instead of a struct enables a
generic implementation to store and extract layer levels.

Add KUnit tests to check the identification of a layer level from a
deny_masks_t, and the computation of a deny_masks_t from an access right
with its layer level or a layer_mask_t array.

Audit event sample:

  type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=fs.ioctl_dev path="/dev/tty" dev="devtmpfs" ino=9 ioctlcmd=0x5401

Cc: Günther Noack <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mickaël Salaün <[email protected]>

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