CVE-2026-31675: net/sched: sch_netem: fix out-of-bounds access in packet corruption

CVE-2026-31675: net/sched: sch_netem: fix out-of-bounds access in packet corruption

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

net/sched: sch_netem: fix out-of-bounds access in packet corruption

In netem_enqueue(), the packet corruption logic uses
get_random_u32_below(skb_headlen(skb)) to select an index for
modifying skb->data. When an AF_PACKET TX_RING sends fully non-linear
packets over an IPIP tunnel, skb_headlen(skb) evaluates to 0.

Passing 0 to get_random_u32_below() takes the variable-ceil slow path
which returns an unconstrained 32-bit random integer. Using this
unconstrained value as an offset into skb->data results in an
out-of-bounds memory access.

Fix this by verifying skb_headlen(skb) is non-zero before attempting
to corrupt the linear data area. Fully non-linear packets will silently
bypass the corruption logic.

The Linux kernel CVE team has assigned CVE-2026-31675 to this issue.


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

	Issue introduced in 2.6.16 with commit c865e5d99e25a171e8262fc0f7ba608568633c64 and fixed in 6.6.134 with commit a14b56863348686dd0387eea8ce66b85cf455908
	Issue introduced in 2.6.16 with commit c865e5d99e25a171e8262fc0f7ba608568633c64 and fixed in 6.12.81 with commit 13a66ca1e235d4bcd53d12d4c68490cad7f8e46f
	Issue introduced in 2.6.16 with commit c865e5d99e25a171e8262fc0f7ba608568633c64 and fixed in 6.18.22 with commit 3a2999704ac36cfb4041fed3652d26a3373e8d12
	Issue introduced in 2.6.16 with commit c865e5d99e25a171e8262fc0f7ba608568633c64 and fixed in 6.19.12 with commit 4fd258e281fa8bc15e9ce2c7691941537e9258ad
	Issue introduced in 2.6.16 with commit c865e5d99e25a171e8262fc0f7ba608568633c64 and fixed in 7.0 with commit d64cb81dcbd54927515a7f65e5e24affdc73c14b

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-2026-31675
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:
	net/sched/sch_netem.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/a14b56863348686dd0387eea8ce66b85cf455908
	https://git.kernel.org/stable/c/13a66ca1e235d4bcd53d12d4c68490cad7f8e46f
	https://git.kernel.org/stable/c/3a2999704ac36cfb4041fed3652d26a3373e8d12
	https://git.kernel.org/stable/c/4fd258e281fa8bc15e9ce2c7691941537e9258ad
	https://git.kernel.org/stable/c/d64cb81dcbd54927515a7f65e5e24affdc73c14b