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Subject[PATCH 4.14 20/33] net: sched: Fix a possible null-pointer dereference in dequeue_func()
Date
From: Jia-Ju Bai <baijiaju1990@gmail.com>

[ Upstream commit 051c7b39be4a91f6b7d8c4548444e4b850f1f56c ]

In dequeue_func(), there is an if statement on line 74 to check whether
skb is NULL:
if (skb)

When skb is NULL, it is used on line 77:
prefetch(&skb->end);

Thus, a possible null-pointer dereference may occur.

To fix this bug, skb->end is used when skb is not NULL.

This bug is found by a static analysis tool STCheck written by us.

Fixes: 76e3cc126bb2 ("codel: Controlled Delay AQM")
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/sch_codel.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -71,10 +71,10 @@ static struct sk_buff *dequeue_func(stru
struct Qdisc *sch = ctx;
struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);

- if (skb)
+ if (skb) {
sch->qstats.backlog -= qdisc_pkt_len(skb);
-
- prefetch(&skb->end); /* we'll need skb_shinfo() */
+ prefetch(&skb->end); /* we'll need skb_shinfo() */
+ }
return skb;
}


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