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Date: Sat, 17 Dec 2022 13:37:15 -0800 From: Cong Wang <xiyou.wangcong@...il.com> To: Paolo Abeni <pabeni@...hat.com> Cc: Jun Nie <jun.nie@...aro.org>, jhs@...atatu.com, jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net v2] net: sched: ematch: reject invalid data On Thu, Dec 15, 2022 at 01:50:43PM +0100, Paolo Abeni wrote: > On Wed, 2022-12-14 at 10:20 +0800, Jun Nie wrote: > > --- > > net/sched/em_cmp.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/net/sched/em_cmp.c b/net/sched/em_cmp.c > > index f17b049ea530..0284394be53f 100644 > > --- a/net/sched/em_cmp.c > > +++ b/net/sched/em_cmp.c > > @@ -22,9 +22,14 @@ static int em_cmp_match(struct sk_buff *skb, struct tcf_ematch *em, > > struct tcf_pkt_info *info) > > { > > struct tcf_em_cmp *cmp = (struct tcf_em_cmp *) em->data; > > - unsigned char *ptr = tcf_get_base_ptr(skb, cmp->layer) + cmp->off; > > + unsigned char *ptr; > > u32 val = 0; > > > > + if (!cmp) > > + return 0; > > It feels like this is papering over the real issue. Why em->data is > NULL here? why other ematches are not afflicted by this issue? > > is em->data really NULL or some small value instead? KASAN seams to > tell it's a small value, not 0, so this patch should not avoid the > oops. Have you tested it vs the reproducer? Right. I think I have found the root cause, let me test my patch to see if it makes syzbot happy. Thanks.
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