CVE-2026-46273: ibmveth: Disable GSO for packets with small MSS

CVE-2026-46273: ibmveth: Disable GSO for packets with small MSS

[Greg Kroah-Hartman]

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

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

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

ibmveth: Disable GSO for packets with small MSS

Some physical adapters on Power systems do not support segmentation
offload when the MSS is less than 224 bytes. Attempting to send such
packets causes the adapter to freeze, stopping all traffic until
manually reset.

Implement ndo_features_check to disable GSO for packets with small MSS
values. The network stack will perform software segmentation instead.

The 224-byte minimum matches ibmvnic
commit <f10b09ef687f> ("ibmvnic: Enforce stronger sanity checks
on GSO packets")
which uses the same physical adapters in SEA configurations.

The issue occurs specifically when the hardware attempts to perform
segmentation (gso_segs > 1) with a small MSS. Single-segment GSO packets
(gso_segs == 1) do not trigger the problematic LSO code path and are
transmitted normally without segmentation.

Add an ndo_features_check callback to disable GSO when MSS < 224 bytes.
Also call vlan_features_check() to ensure proper handling of VLAN packets,
particularly QinQ (802.1ad) configurations where the hardware parser may
not support certain offload features.

Validated using iptables to force small MSS values. Without the fix,
the adapter freezes. With the fix, packets are segmented in software
and transmission succeeds. Comprehensive regression testing completedd
(MSS tests, performance, stability).

The Linux kernel CVE team has assigned CVE-2026-46273 to this issue.


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

	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 5.10.258 with commit 86fc64584811d43c9ccd74447de58620189d8b77
	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 5.15.209 with commit 9a5e984d7af910e46dcbed3ce77873e000a4f77d
	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 6.1.175 with commit 1cdf5dbcec988d06f5f720bdf89e91073f77fa10
	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 6.6.140 with commit 82bc89fbb82d9396fb4eaee8720ea85e2e787957
	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 6.12.88 with commit db8012c631cb845e9ae2b4b531e17d86c9519755
	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 6.18.30 with commit c1f261863e65b508f37416dfbc5c5d911c9b9233
	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 7.0.7 with commit 3af24f0c4c31f18a4a2d927990759194832bb6e9
	Issue introduced in 4.2 with commit 8641dd85799f85bef5f0d1f87356aaa12cb2195e and fixed in 7.1-rc2 with commit cc427d24ac6442ffdeafd157a63c7c5b73ed4de4

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-2026-46273
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:
	drivers/net/ethernet/ibm/ibmveth.c
	drivers/net/ethernet/ibm/ibmveth.h


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/86fc64584811d43c9ccd74447de58620189d8b77
	https://git.kernel.org/stable/c/9a5e984d7af910e46dcbed3ce77873e000a4f77d
	https://git.kernel.org/stable/c/1cdf5dbcec988d06f5f720bdf89e91073f77fa10
	https://git.kernel.org/stable/c/82bc89fbb82d9396fb4eaee8720ea85e2e787957
	https://git.kernel.org/stable/c/db8012c631cb845e9ae2b4b531e17d86c9519755
	https://git.kernel.org/stable/c/c1f261863e65b508f37416dfbc5c5d911c9b9233
	https://git.kernel.org/stable/c/3af24f0c4c31f18a4a2d927990759194832bb6e9
	https://git.kernel.org/stable/c/cc427d24ac6442ffdeafd157a63c7c5b73ed4de4