Subject: CVE-2024-26885: bpf: Fix DEVMAP_HASH overflow check on 32-bit arches

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

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

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

bpf: Fix DEVMAP_HASH overflow check on 32-bit arches

The devmap code allocates a number hash buckets equal to the next power
of two of the max_entries value provided when creating the map. When
rounding up to the next power of two, the 32-bit variable storing the
number of buckets can overflow, and the code checks for overflow by
checking if the truncated 32-bit value is equal to 0. However, on 32-bit
arches the rounding up itself can overflow mid-way through, because it
ends up doing a left-shift of 32 bits on an unsigned long value. If the
size of an unsigned long is four bytes, this is undefined behaviour, so
there is no guarantee that we'll end up with a nice and tidy 0-value at
the end.

Syzbot managed to turn this into a crash on arm32 by creating a
DEVMAP_HASH with max_entries > 0x80000000 and then trying to update it.
Fix this by moving the overflow check to before the rounding up
operation.

The Linux kernel CVE team has assigned CVE-2024-26885 to this issue.

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

	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 5.10.214 with commit 225da02acdc9
	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 5.10.227 with commit 4b81a9f92b36
	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 5.15.153 with commit c826502bed93
	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 6.1.83 with commit edf7990baa48
	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 6.6.23 with commit 250051acc21f
	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 6.7.11 with commit 22079b3a4233
	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 6.8.2 with commit e89386f62ce9
	Issue introduced in 5.4 with commit 6f9d451ab1a3 and fixed in 6.9 with commit 281d464a34f5

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-2024-26885
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/bpf/devmap.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/225da02acdc97af01b6bc6ce1a3e5362bf01d3fb
	https://git.kernel.org/stable/c/4b81a9f92b3676cb74b907a7a209b3d15bd9a7f9
	https://git.kernel.org/stable/c/c826502bed93970f2fd488918a7b8d5f1d30e2e3
	https://git.kernel.org/stable/c/edf7990baa48de5097daa9ac02e06cb4c798a737
	https://git.kernel.org/stable/c/250051acc21f9d4c5c595e4fcb55986ea08c4691
	https://git.kernel.org/stable/c/22079b3a423382335f47d9ed32114e6c9fe88d7c
	https://git.kernel.org/stable/c/e89386f62ce9a9ab9a94835a9890883c23d9d52c
	https://git.kernel.org/stable/c/281d464a34f540de166cee74b723e97ac2515ec3