CVE-2021-47646: linux kernel Use-After-Free — Fix

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

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-416 Use After Free

Affected Products

Vendor	Product	Versions
linux	linux_kernel	< 4.19.238
linux	linux_kernel	4.20 — 5.4.189
linux	linux_kernel	5.5 — 5.10.110
linux	linux_kernel	5.11 — 5.15.33
linux	linux_kernel	5.16 — 5.16.19
linux	linux_kernel	5.17 — 5.17.2

References

Advisories & Patches

https://git.kernel.org/stable/c/15729ff8143f8135b03988a100a19e66d7cb7ecd https://git.kernel.org/stable/c/4083925bd6dc89216d156474a8076feec904e607 https://git.kernel.org/stable/c/65d8a737452e88f251fe5d925371de6d606df613 https://git.kernel.org/stable/c/931aff627469a75c77b9fd3823146d0575afffd6 https://git.kernel.org/stable/c/abc2129e646af7b43025d90a071f83043f1ae76c https://git.kernel.org/stable/c/cc051f497eac9d8a0d816cd4bffa3415f2724871 https://git.kernel.org/stable/c/f990f0985eda59d4f29fc83fcf300c92b1225d39

Frequently Asked Questions

What is CVE-2021-47646? +

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 It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2021-47646? +

CVE-2021-47646 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2021-47646? +

CVE-2021-47646 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47646? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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