Subject: CVE-2024-42131: mm: avoid overflows in dirty throttling logic

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

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

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

mm: avoid overflows in dirty throttling logic

The dirty throttling logic is interspersed with assumptions that dirty
limits in PAGE_SIZE units fit into 32-bit (so that various multiplications
fit into 64-bits).  If limits end up being larger, we will hit overflows,
possible divisions by 0 etc.  Fix these problems by never allowing so
large dirty limits as they have dubious practical value anyway.  For
dirty_bytes / dirty_background_bytes interfaces we can just refuse to set
so large limits.  For dirty_ratio / dirty_background_ratio it isn't so
simple as the dirty limit is computed from the amount of available memory
which can change due to memory hotplug etc.  So when converting dirty
limits from ratios to numbers of pages, we just don't allow the result to
exceed UINT_MAX.

This is root-only triggerable problem which occurs when the operator
sets dirty limits to >16 TB.

The Linux kernel CVE team has assigned CVE-2024-42131 to this issue.

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

	Fixed in 4.19.320 with commit 2b2d2b8766db
	Fixed in 5.4.282 with commit 4d3817b64eda
	Fixed in 5.10.222 with commit 7a49389771ae
	Fixed in 5.15.163 with commit a25e85361845
	Fixed in 6.1.98 with commit c83ed422c24f
	Fixed in 6.6.39 with commit bd16a7ee339a
	Fixed in 6.9.9 with commit 8e0b5e7f2895
	Fixed in 6.10 with commit 385d838df280

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-2024-42131
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/2b2d2b8766db028bd827af34075f221ae9e9efff
	https://git.kernel.org/stable/c/4d3817b64eda07491bdd86a234629fe0764fb42a
	https://git.kernel.org/stable/c/7a49389771ae7666f4dc3426e2a4594bf23ae290
	https://git.kernel.org/stable/c/a25e8536184516b55ef89ab91dd2eea429de28d2
	https://git.kernel.org/stable/c/c83ed422c24f0d4b264f89291d4fabe285f80dbc
	https://git.kernel.org/stable/c/bd16a7ee339aef3ee4c90cb23902afb6af379ea0
	https://git.kernel.org/stable/c/8e0b5e7f2895eccef5c2a0018b589266f90c4805
	https://git.kernel.org/stable/c/385d838df280eba6c8680f9777bfa0d0bfe7e8b2