CVE-2026-74406: vxlan: Fix potential null-ptr-deref in vxlan_gro_prepare_receive().

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

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

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

vxlan: Fix potential null-ptr-deref in vxlan_gro_prepare_receive().

udp_tunnel_sock_release() could set sk->sk_user_data to NULL
while vxlan_gro_prepare_receive() is running.

Let's check if rcu_dereference_sk_user_data() is NULL after
skb_gro_remcsum_init().

The Linux kernel CVE team has assigned CVE-2026-74406 to this issue.


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

	Issue introduced in 4.7 with commit 5602c48cf87562c2f95b831d690631935e834295 and fixed in 6.1.178 with commit 9c58c729d32e7cea5772cc44929c6cd61e5a31cd
	Issue introduced in 4.7 with commit 5602c48cf87562c2f95b831d690631935e834295 and fixed in 6.6.145 with commit f79c80f173fda9545b220c1f094b65fc06c252d0
	Issue introduced in 4.7 with commit 5602c48cf87562c2f95b831d690631935e834295 and fixed in 6.12.97 with commit 08f40c0d23c67c3aa4224c3311e134999c721fb4
	Issue introduced in 4.7 with commit 5602c48cf87562c2f95b831d690631935e834295 and fixed in 6.18.40 with commit 4a8cde6f7281ea2c4c290f9ad9923b3631defceb
	Issue introduced in 4.7 with commit 5602c48cf87562c2f95b831d690631935e834295 and fixed in 7.1.5 with commit ef44dac2a37f86eeae6b88ed10a6d60b35387dfd
	Issue introduced in 4.7 with commit 5602c48cf87562c2f95b831d690631935e834295 and fixed in 7.2-rc1 with commit 30a45c0bffdd62350261e2f2689fdba426a33578

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-2026-74406
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/9c58c729d32e7cea5772cc44929c6cd61e5a31cd
	https://git.kernel.org/stable/c/f79c80f173fda9545b220c1f094b65fc06c252d0
	https://git.kernel.org/stable/c/08f40c0d23c67c3aa4224c3311e134999c721fb4
	https://git.kernel.org/stable/c/4a8cde6f7281ea2c4c290f9ad9923b3631defceb
	https://git.kernel.org/stable/c/ef44dac2a37f86eeae6b88ed10a6d60b35387dfd
	https://git.kernel.org/stable/c/30a45c0bffdd62350261e2f2689fdba426a33578