CVE-2021-47646: Linux Kernel

High severity, CVSS 7.8. EPSS: 0.3% chance of exploitation in the next 30 days.

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 Linux Kernel: before 4.19.238 (fixed in 4.19.238); from 4.20, before 5.4.189 (fixed in 5.4.189); from 5.5, before 5.10.110 (fixed in 5.10.110); from 5.11, before 5.15.33 (fixed in 5.15.33); from 5.16, before 5.16.19 (fixed in 5.16.19); from 5.17, before 5.17.2 (fixed in 5.17.2)

Published 2025-02-26. Last modified 2026-08-11.