2019-07-29 08:52:26

by Jia-Ju Bai

Subject: [PATCH v2] net: sched: Fix a possible null-pointer dereference in dequeue_func()

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: 79bdc4c862af ("codel: generalize the implementation")
Signed-off-by: Jia-Ju Bai <[email protected]>
---
v2:
* Add a fix tag.
Thank Jiri Pirko for helpful advice.

---
net/sched/sch_codel.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
index 25ef172c23df..30169b3adbbb 100644
--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -71,10 +71,10 @@ static struct sk_buff *dequeue_func(struct codel_vars *vars, void *ctx)
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;
}

--
2.17.0

2019-07-29 12:07:37

by Jiri Pirko

Subject: Re: [PATCH v2] net: sched: Fix a possible null-pointer dereference in dequeue_func()

Mon, Jul 29, 2019 at 10:00:18AM CEST, [email protected] wrote:
>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: 79bdc4c862af ("codel: generalize the implementation")

Looks like this is something being there since the beginning:
commit 76e3cc126bb223013a6b9a0e2a51238d1ef2e409
Author: Eric Dumazet <[email protected]>
Date: Thu May 10 07:51:25 2012 +0000

codel: Controlled Delay AQM


Please adjust "Fixes:".

The fix itself looks fine to me.
Reviewed-by: Jiri Pirko <[email protected]>



>Signed-off-by: Jia-Ju Bai <[email protected]>
>---
>v2:
>* Add a fix tag.
> Thank Jiri Pirko for helpful advice.
>
>---
> net/sched/sch_codel.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
>index 25ef172c23df..30169b3adbbb 100644
>--- a/net/sched/sch_codel.c
>+++ b/net/sched/sch_codel.c
>@@ -71,10 +71,10 @@ static struct sk_buff *dequeue_func(struct codel_vars *vars, void *ctx)
> 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;
> }
>
>--
>2.17.0
>

2019-07-29 12:07:59

by Jia-Ju Bai

Subject: Re: [PATCH v2] net: sched: Fix a possible null-pointer dereference in dequeue_func()

On 2019/7/29 16:18, Jiri Pirko wrote:
> Mon, Jul 29, 2019 at 10:00:18AM CEST, [email protected] wrote:
>> 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: 79bdc4c862af ("codel: generalize the implementation")
> Looks like this is something being there since the beginning:
> commit 76e3cc126bb223013a6b9a0e2a51238d1ef2e409
> Author: Eric Dumazet <[email protected]>
> Date: Thu May 10 07:51:25 2012 +0000
>
> codel: Controlled Delay AQM
>
>
> Please adjust "Fixes:".

Thanks for the advice :)
I have sent a v3 patch.


Best wishes,
Jia-Ju Bai