CVE-2021-47504: io_uring: ensure task_work gets run as part of cancelations

CVE-2021-47504: io_uring: ensure task_work gets run as part of cancelations

[Greg Kroah-Hartman]

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

io_uring: ensure task_work gets run as part of cancelations

If we successfully cancel a work item but that work item needs to be
processed through task_work, then we can be sleeping uninterruptibly
in io_uring_cancel_generic() and never process it. Hence we don't
make forward progress and we end up with an uninterruptible sleep
warning.

While in there, correct a comment that should be IFF, not IIF.

The Linux kernel CVE team has assigned CVE-2021-47504 to this issue.


Affected and fixed versions
===========================

	Fixed in 5.15.8 with commit 8e12976c0c19
	Fixed in 5.16 with commit 78a780602075

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47504
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/io_uring.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/8e12976c0c19ebc14b60046b1348c516a74c25a2
	https://git.kernel.org/stable/c/78a780602075d8b00c98070fa26e389b3b3efa72