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

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

[Jia-Ju Bai]

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 <baijiaju1990@gmail.com>
---
 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

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

[Jiri Pirko]

Mon, Jul 29, 2019 at 04:21:57AM CEST, baijiaju1990@gmail.com 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 <baijiaju1990@gmail.com>

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
>

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

[Jia-Ju Bai]

On 2019/7/29 14:56, Jiri Pirko wrote:
> Mon, Jul 29, 2019 at 04:21:57AM CEST, baijiaju1990@gmail.com 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 <baijiaju1990@gmail.com>
> 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

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

[Jiri Pirko]

Mon, Jul 29, 2019 at 09:32:00AM CEST, baijiaju1990@gmail.com wrote:
>
>
>On 2019/7/29 14:56, Jiri Pirko wrote:
>> Mon, Jul 29, 2019 at 04:21:57AM CEST, baijiaju1990@gmail.com 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 <baijiaju1990@gmail.com>
>> 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

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

[Jia-Ju Bai]

On 2019/7/29 15:41, Jiri Pirko wrote:
> Mon, Jul 29, 2019 at 09:32:00AM CEST, baijiaju1990@gmail.com wrote:
>>
>> On 2019/7/29 14:56, Jiri Pirko wrote:
>>> Mon, Jul 29, 2019 at 04:21:57AM CEST, baijiaju1990@gmail.com 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 <baijiaju1990@gmail.com>
>>> 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