Subject: CVE-2024-26627: scsi: core: Move scsi_host_busy() out of host lock for waking up EH handler

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

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

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

scsi: core: Move scsi_host_busy() out of host lock for waking up EH handler

Inside scsi_eh_wakeup(), scsi_host_busy() is called & checked with host
lock every time for deciding if error handler kthread needs to be waken up.

This can be too heavy in case of recovery, such as:

 - N hardware queues

 - queue depth is M for each hardware queue

 - each scsi_host_busy() iterates over (N * M) tag/requests

If recovery is triggered in case that all requests are in-flight, each
scsi_eh_wakeup() is strictly serialized, when scsi_eh_wakeup() is called
for the last in-flight request, scsi_host_busy() has been run for (N * M -
1) times, and request has been iterated for (N*M - 1) * (N * M) times.

If both N and M are big enough, hard lockup can be triggered on acquiring
host lock, and it is observed on mpi3mr(128 hw queues, queue depth 8169).

Fix the issue by calling scsi_host_busy() outside the host lock. We don't
need the host lock for getting busy count because host the lock never
covers that.

[mkp: Drop unnecessary 'busy' variables pointed out by Bart]

The Linux kernel CVE team has assigned CVE-2024-26627 to this issue.

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

	Issue introduced in 5.5 with commit 6eb045e092ef and fixed in 5.10.210 with commit f5944853f7a9
	Issue introduced in 5.5 with commit 6eb045e092ef and fixed in 5.15.149 with commit d37c1c81419f
	Issue introduced in 5.5 with commit 6eb045e092ef and fixed in 6.1.77 with commit db6338f45971
	Issue introduced in 5.5 with commit 6eb045e092ef and fixed in 6.6.16 with commit 65ead8468c21
	Issue introduced in 5.5 with commit 6eb045e092ef and fixed in 6.7.4 with commit 07e3ca0f17f5
	Issue introduced in 5.5 with commit 6eb045e092ef and fixed in 6.8 with commit 4373534a9850

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-2024-26627
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/scsi/scsi_error.c
	drivers/scsi/scsi_lib.c
	drivers/scsi/scsi_priv.h

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/f5944853f7a961fedc1227dc8f60393f8936d37c
	https://git.kernel.org/stable/c/d37c1c81419fdef66ebd0747cf76fb8b7d979059
	https://git.kernel.org/stable/c/db6338f45971b4285ea368432a84033690eaf53c
	https://git.kernel.org/stable/c/65ead8468c21c2676d4d06f50b46beffdea69df1
	https://git.kernel.org/stable/c/07e3ca0f17f579491b5f54e9ed05173d6c1d6fcb
	https://git.kernel.org/stable/c/4373534a9850627a2695317944898eb1283a2db0