linux-cve-announce - CVE-2022-50530: blk-mq: fix null pointer dereference in blk_mq_clear_rq

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Message-ID: <2025100707-CVE-2022-50530-ef6b@gregkh>
Date: Tue,  7 Oct 2025 17:19:17 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-50530: blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping()

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping()

Our syzkaller report a null pointer dereference, root cause is
following:

__blk_mq_alloc_map_and_rqs
 set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs
  blk_mq_alloc_map_and_rqs
   blk_mq_alloc_rqs
    // failed due to oom
    alloc_pages_node
    // set->tags[hctx_idx] is still NULL
    blk_mq_free_rqs
     drv_tags = set->tags[hctx_idx];
     // null pointer dereference is triggered
     blk_mq_clear_rq_mapping(drv_tags, ...)

This is because commit 63064be150e4 ("blk-mq:
Add blk_mq_alloc_map_and_rqs()") merged the two steps:

1) set->tags[hctx_idx] = blk_mq_alloc_rq_map()
2) blk_mq_alloc_rqs(..., set->tags[hctx_idx])

into one step:

set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs()

Since tags is not initialized yet in this case, fix the problem by
checking if tags is NULL pointer in blk_mq_clear_rq_mapping().

The Linux kernel CVE team has assigned CVE-2022-50530 to this issue.


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

	Issue introduced in 5.16 with commit 63064be150e4b1ba1e4af594ef5aa81adf21a52d and fixed in 6.0.6 with commit 6a440e6d04431e774dc084abe88c106e2a474c1a
	Issue introduced in 5.16 with commit 63064be150e4b1ba1e4af594ef5aa81adf21a52d and fixed in 6.1 with commit 76dd298094f484c6250ebd076fa53287477b2328

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-2022-50530
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:
	block/blk-mq.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/6a440e6d04431e774dc084abe88c106e2a474c1a
	https://git.kernel.org/stable/c/76dd298094f484c6250ebd076fa53287477b2328