CVE-2021-47254

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.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• 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
• 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