Subject: CVE-2024-42102: Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again"

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

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

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

Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again"

Patch series "mm: Avoid possible overflows in dirty throttling".

Dirty throttling logic assumes dirty limits in page units fit into
32-bits.  This patch series makes sure this is true (see patch 2/2 for
more details).

This patch (of 2):

This reverts commit 9319b647902cbd5cc884ac08a8a6d54ce111fc78.

The commit is broken in several ways.  Firstly, the removed (u64) cast
from the multiplication will introduce a multiplication overflow on 32-bit
archs if wb_thresh * bg_thresh >= 1<<32 (which is actually common - the
default settings with 4GB of RAM will trigger this).  Secondly, the
div64_u64() is unnecessarily expensive on 32-bit archs.  We have
div64_ul() in case we want to be safe & cheap.  Thirdly, if dirty
thresholds are larger than 1<<32 pages, then dirty balancing is going to
blow up in many other spectacular ways anyway so trying to fix one
possible overflow is just moot.

The Linux kernel CVE team has assigned CVE-2024-42102 to this issue.

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

	Issue introduced in 4.19.307 with commit c593d26fb5d5 and fixed in 4.19.318 with commit 253f9ea7e8e5
	Issue introduced in 5.4.269 with commit 1f12e4b3284d and fixed in 5.4.280 with commit 23a28f5f3f6c
	Issue introduced in 5.10.210 with commit 81e7d2530d45 and fixed in 5.10.222 with commit 145faa3d0368
	Issue introduced in 5.15.149 with commit 5099871b3703 and fixed in 5.15.163 with commit 2820005edae1
	Issue introduced in 6.1.79 with commit 16b1025eaa8f and fixed in 6.1.98 with commit cbbe17a32443
	Issue introduced in 6.6.18 with commit ec18ec230301 and fixed in 6.6.39 with commit f6620df12cb6
	Issue introduced in 6.8 with commit 9319b647902c and fixed in 6.9.9 with commit 000099d71648
	Issue introduced in 6.8 with commit 9319b647902c and fixed in 6.10 with commit 30139c702048
	Issue introduced in 6.7.6 with commit 65977bed167a

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-2024-42102
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:
	mm/page-writeback.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/253f9ea7e8e53a5176bd80ceb174907b10724c1a
	https://git.kernel.org/stable/c/23a28f5f3f6ca1e4184bd0e9631cd0944cf1c807
	https://git.kernel.org/stable/c/145faa3d03688cbb7bbaaecbd84c01539852942c
	https://git.kernel.org/stable/c/2820005edae13b140f2d54267d1bd6bb23915f59
	https://git.kernel.org/stable/c/cbbe17a324437c0ff99881a3ee453da45b228a00
	https://git.kernel.org/stable/c/f6620df12cb6bdcad671d269debbb23573502f9d
	https://git.kernel.org/stable/c/000099d71648504fb9c7a4616f92c2b70c3e44ec
	https://git.kernel.org/stable/c/30139c702048f1097342a31302cbd3d478f50c63