linux-kernel - Re: [PATCH] icmp: Fixed bug in raw sockets causing incorrect ICMP SNMP counter values

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Message-ID: <CAL=9YSUt2j6tgP2OXntHn-_TcFz4i_=WQ9fo86sEZBLW9afbvw@mail.gmail.com>
Date:	Mon, 12 Oct 2015 00:14:46 +0100
From:	Ben Cox <ben@...jojo.co.uk>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ben Cox <ben@...jojo.co.uk>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	ben+patches@...jojo.co.uk, David L Stevens <dlstevens@...ibm.com>
Subject: Re: [PATCH] icmp: Fixed bug in raw sockets causing incorrect ICMP
 SNMP counter values

Nice!

That works in my head at least, Sorry about not seeing that fairly
glaring memory issue there.

Are you sure " skb->transport_header += iphlen; " won't have a knock
on affect when it's given to NF_HOOK ( as in, would a potential
userspace program get something it does not expect anymore ) ?

How does submission work at this point if the above is not a issue
(apologies if this is already in a FAQ somewhere I missed)?

On Mon, Oct 12, 2015 at 12:09 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Sun, 2015-10-11 at 15:44 -0700, Eric Dumazet wrote:
>> On Sun, 2015-10-11 at 15:43 -0700, Eric Dumazet wrote:
>>
>> > But your code reads 21th byte.
>>
>> BTW, nice catch !
>
> Maybe the following one.
>
> 1) We properly set transport header
> 2) We use icmp_hdr() helper.
>
> diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
> index 561cd4b8fc6e..ffe25cd1f0e0 100644
> --- a/net/ipv4/raw.c
> +++ b/net/ipv4/raw.c
> @@ -406,11 +406,11 @@ static int raw_send_hdrinc(struct sock *sk, struct flowi4 *fl4,
>                         ip_select_ident(net, skb, NULL);
>
>                 iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
> +               skb->transport_header += iphlen;
> +               if (iph->protocol == IPPROTO_ICMP &&
> +                   length >= iphlen + sizeof(struct icmphdr))
> +                       icmp_out_count(net, icmp_hdr(skb)->type);
>         }
> -       if (iph->protocol == IPPROTO_ICMP)
> -               icmp_out_count(net, ((struct icmphdr *)
> -                       skb_transport_header(skb))->type);
> -
>         err = NF_HOOK(NFPROTO_IPV4, NF_INET_LOCAL_OUT, sk, skb,
>                       NULL, rt->dst.dev, dst_output_sk);
>         if (err > 0)
>
>
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