CVE-2026-63993: vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu()

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

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

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

vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu()

skb_tunnel_check_pmtu() can change skb->head.

Reusing old_iph afer skb_tunnel_check_pmtu() can cause an UAF.

Use instead ip_hdr(skb) as done in drivers/net/bareudp.c
and drivers/net/geneve.c.

Found by Sashiko.

The Linux kernel CVE team has assigned CVE-2026-63993 to this issue.


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

	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 5.10.259 with commit 6b8bfce9d2f774d2c2243e0248e03efb99bba6c0
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 5.15.210 with commit 9257f56ac47ef1976bcd056cf986a9988eeec67a
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.1.176 with commit 8d435d68d71fb875876b722f4136caf74f2f48bd
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.6.143 with commit dc3bfa050f873371e745bdf478b1f5b738e5733d
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.12.93 with commit 609e63312c29aad18026a1d3222e123d4b6b0feb
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 6.18.35 with commit 5303925e360527243b46a440a04667826bbc72b7
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 7.0.12 with commit a493efd4336cf19122ae0e4cbb3d31b32d70deea
	Issue introduced in 5.9 with commit 4cb47a8644cc9eb8ec81190a50e79e6530d0297f and fixed in 7.1 with commit 7d9ef0cb271555d8cf39fefe6c981e1493b25ecf

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-2026-63993
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/vxlan/vxlan_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/6b8bfce9d2f774d2c2243e0248e03efb99bba6c0
	https://git.kernel.org/stable/c/9257f56ac47ef1976bcd056cf986a9988eeec67a
	https://git.kernel.org/stable/c/8d435d68d71fb875876b722f4136caf74f2f48bd
	https://git.kernel.org/stable/c/dc3bfa050f873371e745bdf478b1f5b738e5733d
	https://git.kernel.org/stable/c/609e63312c29aad18026a1d3222e123d4b6b0feb
	https://git.kernel.org/stable/c/5303925e360527243b46a440a04667826bbc72b7
	https://git.kernel.org/stable/c/a493efd4336cf19122ae0e4cbb3d31b32d70deea
	https://git.kernel.org/stable/c/7d9ef0cb271555d8cf39fefe6c981e1493b25ecf