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

• 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)