CVE-2026-68082 libceph: fix two unsafe bare decodes in decode_lockers()
A malicious OSD can trigger out-of-bounds reads in the Linux kernel Ceph client, potentially causing crashes or leaking memory.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68082?
CVE-2026-68082 is a critical memory corruption vulnerability in Linux, published on 8 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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 ]
Weakness: CWE-125
Which versions are affected by CVE-2026-68082?
How do I fix CVE-2026-68082?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-68082 being exploited?
There is no known exploitation of CVE-2026-68082 in the wild and no public exploit code.
Sources
Also known as AZL-94643, BELL-CVE-2026-68082, DEBIAN-CVE-2026-68082, GHSA-7xmj-3fxq-r5hp, UBUNTU-CVE-2026-68082.