CVE-2021-47646 Information

Description

In the Linux kernel the following vulnerability has been resolved:

Revert \Revert lock bfq: honor already-setup queue merges\

A crash [1] happened to be triggered in conjunction with commit 2d52c58b9c9b (lock bfq: honor already-setup queue merges). The latter was then reverted by commit ebc69e897e17 (\Revert lock 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 (lock bfq: reset last_bfqq_created on group change).

So there is no point in keeping commit 2d52c58b9c9b (lock bfq: honor already-setup queue merges) out. This commit restores it.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=214503

Reference

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