Subject: CVE-2024-43889: padata: Fix possible divide-by-0 panic in padata_mt_helper()

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

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

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

padata: Fix possible divide-by-0 panic in padata_mt_helper()

We are hit with a not easily reproducible divide-by-0 panic in padata.c at
bootup time.

  [   10.017908] Oops: divide error: 0000 1 PREEMPT SMP NOPTI
  [   10.017908] CPU: 26 PID: 2627 Comm: kworker/u1666:1 Not tainted 6.10.0-15.el10.x86_64 #1
  [   10.017908] Hardware name: Lenovo ThinkSystem SR950 [7X12CTO1WW]/[7X12CTO1WW], BIOS [PSE140J-2.30] 07/20/2021
  [   10.017908] Workqueue: events_unbound padata_mt_helper
  [   10.017908] RIP: 0010:padata_mt_helper+0x39/0xb0
    :
  [   10.017963] Call Trace:
  [   10.017968]  <TASK>
  [   10.018004]  ? padata_mt_helper+0x39/0xb0
  [   10.018084]  process_one_work+0x174/0x330
  [   10.018093]  worker_thread+0x266/0x3a0
  [   10.018111]  kthread+0xcf/0x100
  [   10.018124]  ret_from_fork+0x31/0x50
  [   10.018138]  ret_from_fork_asm+0x1a/0x30
  [   10.018147]  </TASK>

Looking at the padata_mt_helper() function, the only way a divide-by-0
panic can happen is when ps->chunk_size is 0.  The way that chunk_size is
initialized in padata_do_multithreaded(), chunk_size can be 0 when the
min_chunk in the passed-in padata_mt_job structure is 0.

Fix this divide-by-0 panic by making sure that chunk_size will be at least
1 no matter what the input parameters are.

The Linux kernel CVE team has assigned CVE-2024-43889 to this issue.

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

	Issue introduced in 5.8 with commit 004ed42638f4 and fixed in 5.10.224 with commit ab8b397d5997
	Issue introduced in 5.8 with commit 004ed42638f4 and fixed in 5.15.165 with commit 8f5ffd2af727
	Issue introduced in 5.8 with commit 004ed42638f4 and fixed in 6.1.105 with commit a29cfcb848c3
	Issue introduced in 5.8 with commit 004ed42638f4 and fixed in 6.6.46 with commit 924f788c906d
	Issue introduced in 5.8 with commit 004ed42638f4 and fixed in 6.10.5 with commit da0ffe84fcc1
	Issue introduced in 5.8 with commit 004ed42638f4 and fixed in 6.11 with commit 6d45e1c948a8

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-2024-43889
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:
	kernel/padata.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/ab8b397d5997d8c37610252528edc54bebf9f6d3
	https://git.kernel.org/stable/c/8f5ffd2af7274853ff91d6cd62541191d9fbd10d
	https://git.kernel.org/stable/c/a29cfcb848c31f22b4de6a531c3e1d68c9bfe09f
	https://git.kernel.org/stable/c/924f788c906dccaca30acab86c7124371e1d6f2c
	https://git.kernel.org/stable/c/da0ffe84fcc1627a7dff82c80b823b94236af905
	https://git.kernel.org/stable/c/6d45e1c948a8b7ed6ceddb14319af69424db730c