net_sched: properly check for empty skb array on error path

First, the check of &q->ring.queue against NULL is wrong, it
is always false. We should check the value rather than the address.

Secondly, we need the same check in pfifo_fast_reset() too,
as both ->reset() and ->destroy() are called in qdisc_destroy().

Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array")
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 981c08f..876fab2 100644 (file)
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -659,6 +659,12 @@ static void pfifo_fast_reset(struct Qdisc *qdisc)
                struct skb_array *q = band2list(priv, band);
                struct sk_buff *skb;
 
+               /* NULL ring is possible if destroy path is due to a failed
+                * skb_array_init() in pfifo_fast_init() case.
+                */
+               if (!q->ring.queue)
+                       continue;
+
                while ((skb = skb_array_consume_bh(q)) != NULL)
                        kfree_skb(skb);
        }
@@ -719,7 +725,7 @@ static void pfifo_fast_destroy(struct Qdisc *sch)
                /* NULL ring is possible if destroy path is due to a failed
                 * skb_array_init() in pfifo_fast_init() case.
                 */
-               if (!&q->ring.queue)
+               if (!q->ring.queue)
                        continue;
                /* Destroy ring but no need to kfree_skb because a call to
                 * pfifo_fast_reset() has already done that work.