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

Ben Hutchings
2016-08-14T12:06:08Z

From: Eric Dumazet <edumazet@google.com>

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@google.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: not using qdisc_qstats_drop()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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;
}