Messages in this thread | | | From | Eric Dumazet <> | Date | Fri, 10 Jun 2022 00:35:04 -0700 | Subject | Re: [PATCH] fq_codel: Discard problematic packets with pkt_len 0 |
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On Fri, Jun 10, 2022 at 12:32 AM Eric Dumazet <edumazet@google.com> wrote: > > On Fri, Jun 10, 2022 at 12:07 AM Di Zhu <zhudi2@huawei.com> wrote: > > > > Syzbot found an issue [1]: fq_codel_drop() try to drop a flow whitout any > > skbs, that is, the flow->head is null. > > The root cause is that: when the first queued skb with pkt_len 0, backlogs > > of the flow that this skb enqueued is still 0 and if sch->limit is set to > > 0 then fq_codel_drop() will be called. At this point, the backlogs of all > > flows are all 0, so flow with idx 0 is selected to drop, but this flow have > > not any skbs. > > skb with pkt_len 0 can break existing processing logic, so just discard > > these invalid skbs. > > > > LINK: [1] https://syzkaller.appspot.com/bug?id=0b84da80c2917757915afa89f7738a9d16ec96c5 > > > > Reported-by: syzbot+7a12909485b94426aceb@syzkaller.appspotmail.com > > Signed-off-by: Di Zhu <zhudi2@huawei.com> > > --- > > net/sched/sch_fq_codel.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c > > index 839e1235db05..c0f82b7358e1 100644 > > --- a/net/sched/sch_fq_codel.c > > +++ b/net/sched/sch_fq_codel.c > > @@ -191,6 +191,9 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch, > > unsigned int pkt_len; > > bool memory_limited; > > > > + if (unlikely(!qdisc_pkt_len(skb))) > > + return qdisc_drop(skb, sch, to_free); > > + > > > This has been discussed in the past. >
https://www.spinics.net/lists/netdev/msg777503.html
> Feeding ndo_start_xmit() in hundreds of drivers with zero-length > packets will crash anyway. > > We are not going to add such silly tests in all qdiscs, and then all > ndo_start_xmit(), since qdiscs are not mandatory. > > Please instead fix BPF layer, instead of hundreds of drivers/qdiscs.
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