From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f193.google.com ([209.85.192.193]:34625 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750715AbeCOFTu (ORCPT ); Thu, 15 Mar 2018 01:19:50 -0400 Received: by mail-pf0-f193.google.com with SMTP id j20so2437581pfi.1 for ; Wed, 14 Mar 2018 22:19:50 -0700 (PDT) Subject: Re: [PATCH v2 net] net: sched: fix uses after free From: John Fastabend To: Eric Dumazet , "David S . Miller" Cc: netdev , Eric Dumazet , Jamal Hadi Salim References: <20180315015300.233327-1-edumazet@google.com> <5b7c5a08-4225-9f20-2a2c-57767a36a967@gmail.com> Message-ID: Date: Wed, 14 Mar 2018 22:19:38 -0700 MIME-Version: 1.0 In-Reply-To: <5b7c5a08-4225-9f20-2a2c-57767a36a967@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org List-ID: On 03/14/2018 08:10 PM, John Fastabend wrote: > On 03/14/2018 06:53 PM, Eric Dumazet wrote: >> syzbot reported one use-after-free in pfifo_fast_enqueue() [1] >> >> Issue here is that we can not reuse skb after a successful skb_array_produce() >> since another cpu might have consumed it already. >> >> I believe a similar problem exists in try_bulk_dequeue_skb_slow() >> in case we put an skb into qdisc_enqueue_skb_bad_txq() for lockless qdisc. >> > > [...] > >> Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array") >> Signed-off-by: Eric Dumazet >> Reported-by: syzbot+ed43b6903ab968b16f54@syzkaller.appspotmail.com >> Cc: John Fastabend >> Cc: Jamal Hadi Salim >> Cc: Cong Wang >> Cc: Jiri Pirko >> --- >> net/sched/sch_generic.c | 22 +++++++++++++--------- >> 1 file changed, 13 insertions(+), 9 deletions(-) >> > > Thanks! > > Acked-by: John Fastabend > >> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c >> index 190570f21b208d5a17943360a3a6f85e1c2a2187..7e3fbe9cc936be376b66a5b12bf8957c3b601f2c 100644 >> --- a/net/sched/sch_generic.c >> +++ b/net/sched/sch_generic.c >> @@ -106,6 +106,14 @@ static inline void qdisc_enqueue_skb_bad_txq(struct Qdisc *q, >> >> __skb_queue_tail(&q->skb_bad_txq, skb); >> >> + if (qdisc_is_percpu_stats(q)) { >> + qdisc_qstats_cpu_backlog_inc(q, skb); > > So I guess the skb access above needs to be removed as > well per your comment in the commit description. But that > can be another patch. > Actually this is fine I read this too quickly on first read. Sorry for the noise. Looks good to me. >> + qdisc_qstats_cpu_qlen_inc(q); >> + } else { >> + qdisc_qstats_backlog_inc(q, skb); >> + q->q.qlen++; >> + } >> + >> if (lock) >> spin_unlock(lock); >> } > >