Subject: CVE-2023-52895: io_uring/poll: don't reissue in case of poll race on multishot request

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

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

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

io_uring/poll: don't reissue in case of poll race on multishot request

A previous commit fixed a poll race that can occur, but it's only
applicable for multishot requests. For a multishot request, we can safely
ignore a spurious wakeup, as we never leave the waitqueue to begin with.

A blunt reissue of a multishot armed request can cause us to leak a
buffer, if they are ring provided. While this seems like a bug in itself,
it's not really defined behavior to reissue a multishot request directly.
It's less efficient to do so as well, and not required to rearm anything
like it is for singleshot poll requests.

The Linux kernel CVE team has assigned CVE-2023-52895 to this issue.

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

	Issue introduced in 6.1.7 with commit c06015ebc436 and fixed in 6.1.8 with commit 36fc7317cdb1

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-2023-52895
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:
	io_uring/poll.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/36fc7317cdb16cfeae0f879916995037bb615ac4
	https://git.kernel.org/stable/c/8caa03f10bf92cb8657408a6ece6a8a73f96ce13