Subject: Re: net/ipv4: warning in nf_nat_ipv4_fn

From: Florian Westphal <[email-masked]>
Date: Wed, 8 Feb 2017 23:10:06 +0100

Andrey Konovalov <[email-masked]> 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.