[PATCH 3.16 192/305] netem: fix a use after free

[Ben Hutchings]

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit 21de12ee5568fd1aec47890c72967abf791ac80a upstream.

If the packet was dropped by lower qdisc, then we must not
access it later.

Save qdisc_pkt_len(skb) in a temp variable.

Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: WANG Cong <xiyou.wangcong@xxxxxxxxx>
Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Cc: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: not using qdisc_qstats_drop()]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/sched/sch_netem.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -606,14 +606,14 @@ deliver:
 #endif
 
 			if (q->qdisc) {
+				unsigned int pkt_len = qdisc_pkt_len(skb);
 				int err = qdisc_enqueue(skb, q->qdisc);
 
-				if (unlikely(err != NET_XMIT_SUCCESS)) {
-					if (net_xmit_drop_count(err)) {
-						sch->qstats.drops++;
-						qdisc_tree_reduce_backlog(sch, 1,
-									  qdisc_pkt_len(skb));
-					}
+				if (err != NET_XMIT_SUCCESS &&
+				    net_xmit_drop_count(err)) {
+					sch->qstats.drops++;
+					qdisc_tree_reduce_backlog(sch, 1,
+								  pkt_len);
 				}
 				goto tfifo_dequeue;
 			}