Subject: CVE-2021-47369: s390/qeth: fix NULL deref in qeth_clear_working_pool_list()

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

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

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

s390/qeth: fix NULL deref in qeth_clear_working_pool_list()

When qeth_set_online() calls qeth_clear_working_pool_list() to roll
back after an error exit from qeth_hardsetup_card(), we are at risk of
accessing card->qdio.in_q before it was allocated by
qeth_alloc_qdio_queues() via qeth_mpc_initialize().

qeth_clear_working_pool_list() then dereferences NULL, and by writing to
queue->bufs[i].pool_entry scribbles all over the CPU's lowcore.
Resulting in a crash when those lowcore areas are used next (eg. on
the next machine-check interrupt).

Such a scenario would typically happen when the device is first set
online and its queues aren't allocated yet. An early IO error or certain
misconfigs (eg. mismatched transport mode, bad portno) then cause us to
error out from qeth_hardsetup_card() with card->qdio.in_q still being
NULL.

Fix it by checking the pointer for NULL before accessing it.

Note that we also have (rare) paths inside qeth_mpc_initialize() where
a configuration change can cause us to free the existing queues,
expecting that subsequent code will allocate them again. If we then
error out before that re-allocation happens, the same bug occurs.

Root-caused-by: Heiko Carstens <[email-masked]>

The Linux kernel CVE team has assigned CVE-2021-47369 to this issue.

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

	Issue introduced in 5.9 with commit eff73e16ee11 and fixed in 5.10.70 with commit db94f89e1dad
	Issue introduced in 5.9 with commit eff73e16ee11 and fixed in 5.14.9 with commit 9b00fb12cdc9
	Issue introduced in 5.9 with commit eff73e16ee11 and fixed in 5.15 with commit 248f064af222
	Issue introduced in 5.7.16 with commit b2400fe7e101
	Issue introduced in 5.8.2 with commit 22697ca855c0

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-2021-47369
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/s390/net/qeth_core_main.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/db94f89e1dadf693c15c2d60de0c34777cea5779
	https://git.kernel.org/stable/c/9b00fb12cdc9d8d1c3ffe82a78e74738127803fc
	https://git.kernel.org/stable/c/248f064af222a1f97ee02c84a98013dfbccad386