CVE-2026-89654

Summary

In the Linux kernel, the following vulnerability has been resolved:

ceph: fix UAF in check_new_map() on session freed during unlock

check_new_map() iterates mdsc->sessions[] and for each active session drops mdsc->mutex to perform per-session operations. The forced-close path (rank removed from map) correctly takes a reference on s via ceph_get_mds_session() before releasing mdsc->mutex, but three other paths do not:

Path A (address changed): mutex_unlock → mutex_lock(&s->s_mutex) Path B (reconnect): mutex_unlock → send_mds_reconnect(mdsc, s) Path C (active transition): mutex_unlock → mutex_lock(&s->s_mutex)

Without the extra reference, another thread can acquire mdsc->mutex during the unlock window, call __unregister_session() which drops the last reference on s, and free it. The original thread then accesses freed memory via s->s_mutex.

Fix by adding ceph_get_mds_session(s) before each mutex_unlock and ceph_put_mds_session(s) after the corresponding mutex_lock, matching the pattern already used in the forced-close path.

Race timeline (Path A):

Thread A (check_new_map) Thread B (another map update holds mdsc->mutex or session teardown)

s = mdsc->sessions[i] (refcount == 1, held only by sessions[] array)

mutex_unlock(&mdsc->mutex) —> acquires mdsc->mutex __unregister_session(mdsc, s) sessions[i] = NULL ceph_put_mds_session(s) refcount: 1 -> 0 kfree(s) <— freed!

mutex_lock(&s->s_mutex) UAF on freed s->s_mutex

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/21d5be092d947f8d83f76f7ebf3989e7e9230a98
• https://git.kernel.org/stable/c/ee611a7509554c4ca1f54f6aefe592fb1df7ea70

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