CVE-2026-68116: vxlan: mdb: Fix source list corruption on a failed replace

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

vxlan: mdb: Fix source list corruption on a failed replace

When replacing the source list of an MDB remote entry, all existing
sources are first marked for deletion and vxlan_mdb_remote_srcs_add()
is then called to add the new source list. Sources present in the new
list have their deletion mark cleared, and any sources left marked
afterwards are removed.

If vxlan_mdb_remote_srcs_add() fails partway through, its error path
deletes all entries on the remote's source list. That rollback is only
correct for its other caller, vxlan_mdb_remote_add(), where the remote
was just allocated and the list contains solely entries added during
the call. On the replace path the list also holds pre-existing sources,
so a failed replace tears them down together with their (S, G)
forwarding entries instead of leaving the entry unchanged.

This is reachable from an existing (*, G) remote. An EXCLUDE filter
that loses sources starts forwarding traffic that should be blocked,
while an INCLUDE filter that loses sources drops traffic that should be
forwarded.

Mark entries created during the current pass with a new
VXLAN_SGRP_F_NEW flag. On failure, delete only those entries and clear
the deletion mark on the pre-existing ones, so a failed replace leaves
the source list untouched. Retain the flag until the whole operation
succeeds and then clear it. Also stop vxlan_mdb_remote_src_add() from
deleting a pre-existing entry it only looked up when adding that
entry's forwarding entry fails.

The Linux kernel CVE team has assigned CVE-2026-68116 to this issue.


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

	Issue introduced in 6.4 with commit a3a48de5eade770e911d35291217bdd69ce04ef1 and fixed in 6.6.148 with commit 5bc8fc1d2ff802eec839e03adef5df597421898d
	Issue introduced in 6.4 with commit a3a48de5eade770e911d35291217bdd69ce04ef1 and fixed in 6.12.101 with commit 2c54dff57606590fa4abec46bab6bea3133f1539
	Issue introduced in 6.4 with commit a3a48de5eade770e911d35291217bdd69ce04ef1 and fixed in 6.18.42 with commit 79370b573e92e8f190eb5f9a511fa5398340d8b2
	Issue introduced in 6.4 with commit a3a48de5eade770e911d35291217bdd69ce04ef1 and fixed in 7.1.6 with commit 54a3c27b357dfb34f327f89bfadeb998bef8051e
	Issue introduced in 6.4 with commit a3a48de5eade770e911d35291217bdd69ce04ef1 and fixed in 7.2-rc5 with commit dcd9b465965422b9654f6026e8a2fa8984f74c3c

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-2026-68116
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_mdb.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/5bc8fc1d2ff802eec839e03adef5df597421898d
	https://git.kernel.org/stable/c/2c54dff57606590fa4abec46bab6bea3133f1539
	https://git.kernel.org/stable/c/79370b573e92e8f190eb5f9a511fa5398340d8b2
	https://git.kernel.org/stable/c/54a3c27b357dfb34f327f89bfadeb998bef8051e
	https://git.kernel.org/stable/c/dcd9b465965422b9654f6026e8a2fa8984f74c3c