xfrm: Add refcount handling to queued policies

We need to ensure that policies can't go away as long as the hold timer
is armed, so take a refcont when we arm the timer and drop one if we
delete it.

Bug was introduced with git commit a0073fe1 ("xfrm: Add a state
resolution packet queue")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -334,7 +334,8 @@ static void xfrm_policy_kill(struct xfrm_policy *policy)
 
 	atomic_inc(&policy->genid);
 
-	del_timer(&policy->polq.hold_timer);
+	if (del_timer(&policy->polq.hold_timer))
+		xfrm_pol_put(policy);
 	xfrm_queue_purge(&policy->polq.hold_queue);
 
 	if (del_timer(&policy->timer))
@@ -589,7 +590,8 @@ static void xfrm_policy_requeue(struct xfrm_policy *old,
 
 	spin_lock_bh(&pq->hold_queue.lock);
 	skb_queue_splice_init(&pq->hold_queue, &list);
-	del_timer(&pq->hold_timer);
+	if (del_timer(&pq->hold_timer))
+		xfrm_pol_put(old);
 	spin_unlock_bh(&pq->hold_queue.lock);
 
 	if (skb_queue_empty(&list))
@@ -600,7 +602,8 @@ static void xfrm_policy_requeue(struct xfrm_policy *old,
 	spin_lock_bh(&pq->hold_queue.lock);
 	skb_queue_splice(&list, &pq->hold_queue);
 	pq->timeout = XFRM_QUEUE_TMO_MIN;
-	mod_timer(&pq->hold_timer, jiffies);
+	if (!mod_timer(&pq->hold_timer, jiffies))
+		xfrm_pol_hold(new);
 	spin_unlock_bh(&pq->hold_queue.lock);
 }
 
@@ -1787,8 +1790,9 @@ static void xfrm_policy_queue_process(unsigned long arg)
 			goto purge_queue;
 
 		pq->timeout = pq->timeout << 1;
-		mod_timer(&pq->hold_timer, jiffies + pq->timeout);
-		return;
+		if (!mod_timer(&pq->hold_timer, jiffies + pq->timeout))
+			xfrm_pol_hold(pol);
+	goto out;
 	}
 
 	dst_release(dst);
@@ -1819,11 +1823,14 @@ static void xfrm_policy_queue_process(unsigned long arg)
 		err = dst_output(skb);
 	}
 
+out:
+	xfrm_pol_put(pol);
 	return;
 
 purge_queue:
 	pq->timeout = 0;
 	xfrm_queue_purge(&pq->hold_queue);
+	xfrm_pol_put(pol);
 }
 
 static int xdst_queue_output(struct sk_buff *skb)
@@ -1831,7 +1838,8 @@ static int xdst_queue_output(struct sk_buff *skb)
 	unsigned long sched_next;
 	struct dst_entry *dst = skb_dst(skb);
 	struct xfrm_dst *xdst = (struct xfrm_dst *) dst;
-	struct xfrm_policy_queue *pq = &xdst->pols[0]->polq;
+	struct xfrm_policy *pol = xdst->pols[0];
+	struct xfrm_policy_queue *pq = &pol->polq;
 
 	if (pq->hold_queue.qlen > XFRM_MAX_QUEUE_LEN) {
 		kfree_skb(skb);
@@ -1850,10 +1858,12 @@ static int xdst_queue_output(struct sk_buff *skb)
 	if (del_timer(&pq->hold_timer)) {
 		if (time_before(pq->hold_timer.expires, sched_next))
 			sched_next = pq->hold_timer.expires;
+		xfrm_pol_put(pol);
 	}
 
 	__skb_queue_tail(&pq->hold_queue, skb);
-	mod_timer(&pq->hold_timer, sched_next);
+	if (!mod_timer(&pq->hold_timer, sched_next))
+		xfrm_pol_hold(pol);
 
 	spin_unlock_bh(&pq->hold_queue.lock);