Subject: CVE-2021-47124: io_uring: fix link timeout refs

From: Greg Kroah-Hartman <[email-masked]>

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

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

io_uring: fix link timeout refs

WARNING: CPU: 0 PID: 10242 at lib/refcount.c:28 refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28
RIP: 0010:refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28
Call Trace:
 __refcount_sub_and_test include/linux/refcount.h:283 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 io_put_req fs/io_uring.c:2140 [inline]
 io_queue_linked_timeout fs/io_uring.c:6300 [inline]
 __io_queue_sqe+0xbef/0xec0 fs/io_uring.c:6354
 io_submit_sqe fs/io_uring.c:6534 [inline]
 io_submit_sqes+0x2bbd/0x7c50 fs/io_uring.c:6660
 __do_sys_io_uring_enter fs/io_uring.c:9240 [inline]
 __se_sys_io_uring_enter+0x256/0x1d60 fs/io_uring.c:9182

io_link_timeout_fn() should put only one reference of the linked timeout
request, however in case of racing with the master request's completion
first io_req_complete() puts one and then io_put_req_deferred() is
called.

The Linux kernel CVE team has assigned CVE-2021-47124 to this issue.

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

	Issue introduced in 5.10.26 with commit 1c20e9040f49 and fixed in 5.10.43 with commit 0b2a990e5d2f
	Issue introduced in 5.10.26 with commit 1c20e9040f49 and fixed in 5.10.55 with commit 6f5d7a45f58d
	Issue introduced in 5.12 with commit 9ae1f8dd372e and fixed in 5.12.10 with commit 876808dba2ff
	Issue introduced in 5.12 with commit 9ae1f8dd372e and fixed in 5.12.19 with commit ff4a96ba5c8f
	Issue introduced in 5.12 with commit 9ae1f8dd372e and fixed in 5.13 with commit a298232ee6b9
	Issue introduced in 5.11.6 with commit 567c81912cec

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-2021-47124
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/0b2a990e5d2f76d020cb840c456e6ec5f0c27530
	https://git.kernel.org/stable/c/6f5d7a45f58d3abe3a936de1441b8d6318f978ff
	https://git.kernel.org/stable/c/876808dba2ff7509bdd7f230c4f374a0caf4f410
	https://git.kernel.org/stable/c/ff4a96ba5c8f9b266706280ff8021d2ef3f17e86
	https://git.kernel.org/stable/c/a298232ee6b9a1d5d732aa497ff8be0d45b5bd82