CVE-2021-47646: Revert "Revert "block, bfq: honor already-setup queue merges""

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-02-26 · updated 2026-08-11
Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: Revert "Revert "block, bfq: honor already-setup queue merges"" A crash [1] happened to be triggered in conjunction with commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq: honor already-setup queue merges""). Yet, the reverted commit was not the one introducing the bug. In fact, it actually triggered a UAF introduced by a different commit, and now fixed by commit d29bd41428cf ("block, bfq: reset last_bfqq_created on group change"). So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges") out. This commit restores it. [1] https://bugzilla.kernel.org/show_bug.cgi?id=214503

Affected products

Linux kernel: before 4.19.238; from 4.20 before 5.4.189; from 5.5 before 5.10.110; from 5.11 before 5.15.33; from 5.16 before 5.16.19; from 5.17 before 5.17.2 — fixed in 4.19.238, 5.10.110, 5.15.33, 5.16.19, 5.17.2, 5.4.189

How to fix

Upgrade to a fixed version: Linux kernel 4.19.238, 5.10.110, 5.15.33, 5.16.19. Check the vendor advisory for mitigations.

References

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