Subject: CVE-2022-48874: misc: fastrpc: Fix use-after-free and race in fastrpc_map_find

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

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

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

misc: fastrpc: Fix use-after-free and race in fastrpc_map_find

Currently, there is a race window between the point when the mutex is
unlocked in fastrpc_map_lookup and the reference count increasing
(fastrpc_map_get) in fastrpc_map_find, which can also lead to
use-after-free.

So lets merge fastrpc_map_find into fastrpc_map_lookup which allows us
to both protect the maps list by also taking the &fl->lock spinlock and
the reference count, since the spinlock will be released only after.
Add take_ref argument to make this suitable for all callers.

The Linux kernel CVE team has assigned CVE-2022-48874 to this issue.

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

	Issue introduced in 5.18 with commit 8f6c1d8c4f0c and fixed in 6.1.8 with commit a50c5c25b6e7
	Issue introduced in 5.18 with commit 8f6c1d8c4f0c and fixed in 6.2 with commit 9446fa1683a7

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-2022-48874
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:
	drivers/misc/fastrpc.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/a50c5c25b6e7d2824698c0e6385f882a18f4a498
	https://git.kernel.org/stable/c/9446fa1683a7e3937d9970248ced427c1983a1c5