CVE-2026-63992: tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()

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

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

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

tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()

In some cases, iptunnel_pmtud_check_icmp() can be called while
skb transport header is not set.

This triggers an out-of-bound access, because
(typeof(skb->transport_header))~0U is 65535.

Access the icmp header based on IPv4 network header,
after making sure icmp->type is present in skb linear part.

Note that iptunnel_pmtud_check_icmpv6()) is fine.

The Linux kernel CVE team has assigned CVE-2026-63992 to this issue.


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

	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 5.10.259 with commit 5a92cb45e34749865d03daf8d3500f77b5f6644c
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 5.15.210 with commit c7b7ec3e69e673c0d6b57f74d21da50c485c598e
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.1.176 with commit 7f4f7efe7f30edd29c4988de01728bf2398217e4
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.6.143 with commit e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.12.93 with commit a096b6e34f602950af9a2b0856cd93a5f4c276d7
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.18.35 with commit 43368636c663cff6e59dde93cf4b8e43ac28eb93
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 7.0.12 with commit cb549df9ce4ee15c9d5b19ddab12cf2128e4313c
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 7.1 with commit 509323077ef79a26ba0c60bb556e45c12c398b2d

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-2026-63992
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/ipv4/ip_tunnel_core.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/5a92cb45e34749865d03daf8d3500f77b5f6644c
	https://git.kernel.org/stable/c/c7b7ec3e69e673c0d6b57f74d21da50c485c598e
	https://git.kernel.org/stable/c/7f4f7efe7f30edd29c4988de01728bf2398217e4
	https://git.kernel.org/stable/c/e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec
	https://git.kernel.org/stable/c/a096b6e34f602950af9a2b0856cd93a5f4c276d7
	https://git.kernel.org/stable/c/43368636c663cff6e59dde93cf4b8e43ac28eb93
	https://git.kernel.org/stable/c/cb549df9ce4ee15c9d5b19ddab12cf2128e4313c
	https://git.kernel.org/stable/c/509323077ef79a26ba0c60bb556e45c12c398b2d