netdev - [PATCH net-next] netem: fix possible NULL deref in netem

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Message-ID: <1372885454.4979.73.camel@edumazet-glaptop>
Date:	Wed, 03 Jul 2013 14:04:14 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	Dan Carpenter <dan.carpenter@...cle.com>
Subject: [PATCH net-next] netem: fix possible NULL deref in netem_dequeue()

From: Eric Dumazet <edumazet@...gle.com>

commit aec0a40a6f7884 ("netem: use rb tree to implement the time queue")
added a regression if a child qdisc is attached to netem, as we perform
a NULL dereference.

Fix this by adding a temporary variable to cache
netem_skb_cb(skb)->time_to_send.

Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/sched/sch_netem.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index ed0082c..ca4a5d5 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -554,10 +554,13 @@ deliver:
 	}
 	p = rb_first(&q->t_root);
 	if (p) {
+		psched_time_t time_to_send;
+
 		skb = netem_rb_to_skb(p);
 
 		/* if more time remaining? */
-		if (netem_skb_cb(skb)->time_to_send <= psched_get_time()) {
+		time_to_send = netem_skb_cb(skb)->time_to_send;
+		if (time_to_send <= psched_get_time()) {
 			rb_erase(p, &q->t_root);
 
 			sch->q.qlen--;
@@ -593,8 +596,7 @@ deliver:
 			if (skb)
 				goto deliver;
 		}
-		qdisc_watchdog_schedule(&q->watchdog,
-					netem_skb_cb(skb)->time_to_send);
+		qdisc_watchdog_schedule(&q->watchdog, time_to_send);
 	}
 
 	if (q->qdisc) {


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