[Patch net v2] net_sched: let qdisc_put() accept NULL pointer

[Patch net v2] net_sched: let qdisc_put() accept NULL pointer

[Cong Wang]

When tcf_block_get() fails in sfb_init(), q->qdisc is still a NULL
pointer which leads to a crash in sfb_destroy(). Similar for
sch_dsmark.

Instead of fixing each separately, Linus suggested to just accept
NULL pointer in qdisc_put(), which would make callers easier.

(For sch_dsmark, the bug probably exists long before commit
6529eaba33f0.)

Fixes: 6529eaba33f0 ("net: sched: introduce tcf block infractructure")
Reported-by: syzbot+d5870a903591faaca4ae@syzkaller.appspotmail.com
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/sched/sch_generic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index ac28f6a5d70e..17bd8f539bc7 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -985,6 +985,9 @@ static void qdisc_destroy(struct Qdisc *qdisc)
 
 void qdisc_put(struct Qdisc *qdisc)
 {
+	if (!qdisc)
+		return;
+
 	if (qdisc->flags & TCQ_F_BUILTIN ||
 	    !refcount_dec_and_test(&qdisc->refcnt))
 		return;
-- 
2.21.0

Re: [Patch net v2] net_sched: let qdisc_put() accept NULL pointer

[Jiri Pirko]

Thu, Sep 12, 2019 at 07:22:30PM CEST, xiyou.wangcong@gmail.com wrote:
>When tcf_block_get() fails in sfb_init(), q->qdisc is still a NULL
>pointer which leads to a crash in sfb_destroy(). Similar for
>sch_dsmark.
>
>Instead of fixing each separately, Linus suggested to just accept
>NULL pointer in qdisc_put(), which would make callers easier.
>
>(For sch_dsmark, the bug probably exists long before commit
>6529eaba33f0.)
>
>Fixes: 6529eaba33f0 ("net: sched: introduce tcf block infractructure")
>Reported-by: syzbot+d5870a903591faaca4ae@syzkaller.appspotmail.com
>Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
>Cc: Jamal Hadi Salim <jhs@mojatatu.com>
>Cc: Jiri Pirko <jiri@resnulli.us>
>Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Acked-by: Jiri Pirko <jiri@mellanox.com>

Thanks!

Re: [Patch net v2] net_sched: let qdisc_put() accept NULL pointer

[David Miller]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Thu, 12 Sep 2019 10:22:30 -0700

> When tcf_block_get() fails in sfb_init(), q->qdisc is still a NULL
> pointer which leads to a crash in sfb_destroy(). Similar for
> sch_dsmark.
> 
> Instead of fixing each separately, Linus suggested to just accept
> NULL pointer in qdisc_put(), which would make callers easier.
> 
> (For sch_dsmark, the bug probably exists long before commit
> 6529eaba33f0.)
> 
> Fixes: 6529eaba33f0 ("net: sched: introduce tcf block infractructure")
> Reported-by: syzbot+d5870a903591faaca4ae@syzkaller.appspotmail.com
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Applied and queued up for -stable, thanks.