CVE-2026-63804

/// Technical description

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

gfs2: fix use-after-free in gfs2_qd_dealloc

gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(),

accesses the superblock object sdp through qd->qd_sbd after freeing qd.

It does so to decrement sd_quota_count and wake up sd_kill_wait.

However, by the time the RCU callback runs, gfs2_put_super() may have

already freed sdp via free_sbd(). This can happen when

gfs2_quota_cleanup() is called during unmount: it disposes of quota

objects via call_rcu() and then waits on sd_kill_wait with a 60-second

timeout. If the timeout expires, or if gfs2_gl_hash_clear() triggers

additional qd_put() calls that schedule more RCU callbacks after the

wait completes, gfs2_put_super() will proceed to free the superblock

while RCU callbacks referencing it are still pending.

Add an rcu_barrier() before free_sbd() in gfs2_put_super() to ensure

all pending RCU callbacks (including gfs2_qd_dealloc) have completed

before the su

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References