CVE-2026-68082libceph: fix two unsafe bare decodes in decode_lockers()

Official description

In the Linux kernel, the following vulnerability has been resolved: libceph: fix two unsafe bare decodes in decode_lockers() decode_lockers() in cls_lock_client.c contains two bare decode operations that allow a malicious or compromised OSD to trigger slab-out-of-bounds reads: 1. ceph_decode_32(p) at the num_lockers field has no preceding bounds check. ceph_start_decoding() accepts struct_len=0 as valid -- the internal ceph_decode_need(p, end, 0, bad) always passes -- so when an OSD sends struct_len=0, ceph_start_decoding() returns success with p == end. The immediately following bare ceph_decode_32(p) then reads 4 bytes past the validated buffer boundary. The garbage value is passed directly to kzalloc_objs() as the locker count. The sibling function decode_watchers() in osd_client.c already uses ceph_decode_32_safe() after its own ceph_start_decoding() call. decode_lockers() was the only site using the bare variant. 2. ceph_decode_8(p) after the decode_locker() loop has no preceding bounds check. If an OSD crafts num_lockers such that the loop advances p exactly to end, the subsequent bare ceph_decode_8(p) reads one byte past the validated buffer boundary. The result is passed directly into *type, which is used as a lock type discriminator by callers, giving an OSD-controlled one-byte OOB read with direct influence over the lock type field. Fix both by replacing bare operations with their safe variants: ceph_decode_32(p) -> ceph_decode_32_safe(p, end, *num_lockers, err_inval) ceph_decode_8(p) -> ceph_decode_8_safe(p, end, *type, err_free_lockers) The goto targets differ intentionally: err_inval: is a new label returning -EINVAL directly. It is used for the pre-allocation failure path where *lockers is not yet allocated and must not be passed to ceph_free_lockers(). err_free_lockers: is the existing label. It is used for the post-allocation failure path where *lockers is allocated and must be freed. ret is set to -EINVAL before ceph_decode_8_safe() so that err_free_lockers returns the correct error code on bounds violation. Without this, err_free_lockers would return a stale ret value (0 from the successful decode_locker() loop), silently swallowing the error. -EINVAL is correct for both failure paths. The data received from the OSD is structurally malformed. -ENOMEM would misrepresent the failure class to callers and to stable@ backporters triaging error paths. Attacker model: a malicious or compromised OSD in a multi-tenant Ceph deployment can trigger this against any kernel client that issues the lock.get_info class method (e.g. during RBD exclusive lock acquisition). [ idryomov: trim changelog, formatting ]

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/c8ade01170a27d8ede0d761c255268af81e417f8
• https://git.kernel.org/stable/c/001835c599899ef1bd3506a815110a6374451554
• https://git.kernel.org/stable/c/7c422364acd93d7da1dfc27d6b54635a269653a1
• https://git.kernel.org/stable/c/02430f6f729b297e803d0605871f0a670b4eafd6
• https://git.kernel.org/stable/c/57ba829804fe6d34bbac3b826c4b15c1caa54862
• https://git.kernel.org/stable/c/89df5d71f83f8e2781286798fd8ae5e42cf5f1a7
• https://git.kernel.org/stable/c/a54be593d0b749161b08a1e56189b2cb9114267a
• https://git.kernel.org/stable/c/a109a556115271ca7896dcda7b4b7e45e156c227