CVE-2026-31406: xfrm: Fix work re-schedule after cancel in xfrm_nat_keepalive_net_fini()

CVE-2026-31406: xfrm: Fix work re-schedule after cancel in xfrm_nat_keepalive_net_fini()

[Greg Kroah-Hartman]

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

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

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

xfrm: Fix work re-schedule after cancel in xfrm_nat_keepalive_net_fini()

After cancel_delayed_work_sync() is called from
xfrm_nat_keepalive_net_fini(), xfrm_state_fini() flushes remaining
states via __xfrm_state_delete(), which calls
xfrm_nat_keepalive_state_updated() to re-schedule nat_keepalive_work.

The following is a simple race scenario:

           cpu0                             cpu1

cleanup_net() [Round 1]
  ops_undo_list()
    xfrm_net_exit()
      xfrm_nat_keepalive_net_fini()
        cancel_delayed_work_sync(nat_keepalive_work);
      xfrm_state_fini()
        xfrm_state_flush()
          xfrm_state_delete(x)
            __xfrm_state_delete(x)
              xfrm_nat_keepalive_state_updated(x)
                schedule_delayed_work(nat_keepalive_work);
  rcu_barrier();
  net_complete_free();
  net_passive_dec(net);
    llist_add(&net->defer_free_list, &defer_free_list);

cleanup_net() [Round 2]
  rcu_barrier();
  net_complete_free()
    kmem_cache_free(net_cachep, net);
                                     nat_keepalive_work()
                                       // on freed net

To prevent this, cancel_delayed_work_sync() is replaced with
disable_delayed_work_sync().

The Linux kernel CVE team has assigned CVE-2026-31406 to this issue.


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

	Issue introduced in 6.11 with commit f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae and fixed in 6.12.80 with commit 32d0f44c2f14d60fe8e920e69a28c11051543ec1
	Issue introduced in 6.11 with commit f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae and fixed in 6.18.21 with commit 2255ed6adbc3100d2c4a83abd9d0396d04b87792
	Issue introduced in 6.11 with commit f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae and fixed in 6.19.11 with commit 21f2fc49ca6faa393c31da33b8a4e6c41fc84c13
	Issue introduced in 6.11 with commit f531d13bdfe3f4f084aaa8acae2cb0f02295f5ae and fixed in 7.0-rc6 with commit daf8e3b253aa760ff9e96c7768a464bc1d6b3c90

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-2026-31406
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/xfrm/xfrm_nat_keepalive.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/32d0f44c2f14d60fe8e920e69a28c11051543ec1
	https://git.kernel.org/stable/c/2255ed6adbc3100d2c4a83abd9d0396d04b87792
	https://git.kernel.org/stable/c/21f2fc49ca6faa393c31da33b8a4e6c41fc84c13
	https://git.kernel.org/stable/c/daf8e3b253aa760ff9e96c7768a464bc1d6b3c90