linux-kernel - Re: net/ipv4: warning in nf_nat_ipv4

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Date:   Wed, 8 Feb 2017 23:10:06 +0100
From:   Florian Westphal <fw@...len.de>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Patrick McHardy <kaber@...sh.net>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv4: warning in nf_nat_ipv4_fn

Andrey Konovalov <andreyknvl@...gle.com> wrote:
> Hi,
> 
> I've got the following error report while fuzzing the kernel with syzkaller.
> 
> On commit 926af6273fc683cd98cd0ce7bf0d04a02eed6742.
> 
> A reproducer and .config are attached.
> 
> WARNING: CPU: 2 PID: 26582 at
> net/ipv4/netfilter/nf_nat_l3proto_ipv4.c:261
> nf_nat_ipv4_fn+0x7f2/0xa50
> net/ipv4/netfilter/nf_nat_l3proto_ipv4.c:261
> Kernel panic - not syncing: panic_on_warn set ...

Thats this assert:
/* We never see fragments: conntrack defrags on pre-routing
 * and local-out, and nf_nat_out protects post-routing.
 */
NF_CT_ASSERT(!ip_is_fragment(ip_hdr(skb)));


... and its wrong. I will send a patch to remove it.