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

gfs2: Fix use-after-free in gfs2_glock_shrink_scan

The GLF_LRU flag is checked under lru_lock in gfs2_glock_remove_from_lru() to
remove the glock from the lru list in __gfs2_glock_put().

On the shrink scan path, the same flag is cleared under lru_lock but because
of cond_resched_lock(&lru_lock) in gfs2_dispose_glock_lru(), progress on the
put side can be made without deleting the glock from the lru list.

Keep GLF_LRU across the race window opened by cond_resched_lock(&lru_lock) to
ensure correct behavior on both sides - clear GLF_LRU after list_del under
lru_lock.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-47254
• https://git.kernel.org/stable/c/0364742decb0f02bc183404868b82896f7992595
• https://git.kernel.org/stable/c/094bf5670e762afa243d2c41a5c4ab71c7447bf4
• https://git.kernel.org/stable/c/1ab19c5de4c537ec0d9b21020395a5b5a6c059b2
• https://git.kernel.org/stable/c/38ce329534500bf4ae71f81df6a37a406cf187b4
• https://git.kernel.org/stable/c/86fd5b27db743a0ce0cc245e3a34813b2aa6ec1d
• https://git.kernel.org/stable/c/92869945cc5b78ee8a1ef90336fe070893e3458a
• https://git.kernel.org/stable/c/a61156314b66456ab6a291ed5deba1ebd002ab3c
• https://git.kernel.org/stable/c/e87ef30fe73e7e10d2c85bdcc778dcec24dca553