xfrm: Allow Set Mark to be Updated Using UPDSA

Allow UPDSA to change "set mark" to permit
policy separation of packet routing decisions from
SA keying in systems that use mark-based routing.

The set mark, used as a routing and firewall mark
for outbound packets, is made update-able which
allows routing decisions to be handled independently
of keying/SA creation. To maintain consistency with
other optional attributes, the set mark is only
updated if sent with a non-zero value.

The per-SA lock and the xfrm_state_lock are taken in
that order to avoid a deadlock with
xfrm_timer_handler(), which also takes the locks in
that order.

Signed-off-by: Nathan Harold <nharold@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_state.c

@@ -1562,6 +1562,15 @@ out:
 		if (x1->curlft.use_time)
 			xfrm_state_check_expire(x1);
 
+		if (x->props.smark.m || x->props.smark.v) {
+			spin_lock_bh(&net->xfrm.xfrm_state_lock);
+
+			x1->props.smark = x->props.smark;
+
+			__xfrm_state_bump_genids(x1);
+			spin_unlock_bh(&net->xfrm.xfrm_state_lock);
+		}
+
 		err = 0;
 		x->km.state = XFRM_STATE_DEAD;
 		__xfrm_state_put(x);