CVE-2026-89562: ip6_gre: fix hardware header length for NBMA tunnels

CVE-2026-89562: ip6_gre: fix hardware header length for NBMA tunnels

[Greg Kroah-Hartman]

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

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

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

ip6_gre: fix hardware header length for NBMA tunnels

ip6gre_tnl_link_config_route() accumulates the lower device's hardware
header length into dev->hard_header_len whenever header_ops is set. This
is incorrect for both users of header_ops.

ip6gretap and ip6erspan have a fixed Ethernet hardware header length.
For an NBMA ip6gre tunnel, ip6gre_header() creates only the GRE header,
the optional FOU or GUE header, and the outer IPv6 header. The lower
device header is headroom needed later, not part of the tunnel device's
hardware header.

Keep the lower device header in needed_headroom. Set hard_header_len to
the tunnel header length only for ARPHRD_IP6GRE devices with header_ops,
and leave the fixed Ethernet header length unchanged for tap and erspan
devices.

The Linux kernel CVE team has assigned CVE-2026-89562 to this issue.


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

	Issue introduced in 5.10 with commit 832ba596494b2c9eac7760259eff2d8b7dcad0ee and fixed in 6.12.109 with commit 8bfe746afee38dd6e4348ddcd22d554789dbb9ff
	Issue introduced in 5.10 with commit 832ba596494b2c9eac7760259eff2d8b7dcad0ee and fixed in 6.18.50 with commit b8282668d8fa7c61b80e8e4890729031c291a16c
	Issue introduced in 5.10 with commit 832ba596494b2c9eac7760259eff2d8b7dcad0ee and fixed in 7.2.4 with commit 565038b0092f65afe384961c0f548d605bf438b9
	Issue introduced in 5.10 with commit 832ba596494b2c9eac7760259eff2d8b7dcad0ee and fixed in 7.3-rc1 with commit 505b6d296c486ef7d1274f279d4c43a172f63224
	Issue introduced in 4.19.162 with commit cf3d9717a5271573fa193c4dfa0df856295d5b15
	Issue introduced in 5.4.82 with commit 187a6daf5db45adc807c85bbe285319107bed198
	Issue introduced in 5.9.13 with commit d9897bb66ce989325b4bf4cdbb6a799e4ac878b6

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-2026-89562
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/ipv6/ip6_gre.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/8bfe746afee38dd6e4348ddcd22d554789dbb9ff
	https://git.kernel.org/stable/c/b8282668d8fa7c61b80e8e4890729031c291a16c
	https://git.kernel.org/stable/c/565038b0092f65afe384961c0f548d605bf438b9
	https://git.kernel.org/stable/c/505b6d296c486ef7d1274f279d4c43a172f63224