2019-07-29 02:22:55

by Jia-Ju Bai

Subject: [PATCH] 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.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
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 07:03:22

by Jiri Pirko

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

Mon, Jul 29, 2019 at 04:21:57AM 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.
>
>Signed-off-by: Jia-Ju Bai <[email protected]>

Fixes tag, please?


>---
> 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 07:33:19

by Jia-Ju Bai

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

On 2019/7/29 14:56, Jiri Pirko wrote:
> Mon, Jul 29, 2019 at 04:21:57AM 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.
>>
>> Signed-off-by: Jia-Ju Bai <[email protected]>
> Fixes tag, please?

Sorry, I do not know what "fixes tag" means...
I just find a possible bug and fix it in this patch.


Best wishes,
Jia-Ju Bai

2019-07-29 08:10:17

by Jiri Pirko

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

Mon, Jul 29, 2019 at 09:32:00AM CEST, [email protected] wrote:
>
>
>On 2019/7/29 14:56, Jiri Pirko wrote:
>> Mon, Jul 29, 2019 at 04:21:57AM 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.
>> >
>> > Signed-off-by: Jia-Ju Bai <[email protected]>
>> Fixes tag, please?
>
>Sorry, I do not know what "fixes tag" means...
>I just find a possible bug and fix it in this patch.

git log |grep Fixes:

If A fix goes to -net tree, it most probably fixes some bug introduced
by some commit in the past. So this tag is to put a reference.


>
>
>Best wishes,
>Jia-Ju Bai

2019-07-29 08:51:58

by Jia-Ju Bai

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

On 2019/7/29 15:41, Jiri Pirko wrote:
> Mon, Jul 29, 2019 at 09:32:00AM CEST, [email protected] wrote:
>>
>> On 2019/7/29 14:56, Jiri Pirko wrote:
>>> Mon, Jul 29, 2019 at 04:21:57AM 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.
>>>>
>>>> Signed-off-by: Jia-Ju Bai <[email protected]>
>>> Fixes tag, please?
>> Sorry, I do not know what "fixes tag" means...
>> I just find a possible bug and fix it in this patch.
> git log |grep Fixes:
>
> If A fix goes to -net tree, it most probably fixes some bug introduced
> by some commit in the past. So this tag is to put a reference.

Thanks for the explanation.
I will add it and submit a v2 patch.


Best wishes,
Jia-Ju Bai