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

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Date:	Sun, 11 Oct 2015 15:10:48 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Cartwright-Cox <ben@...jojo.co.uk>
Cc:	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

On Sun, 2015-10-11 at 20:55 +0000, Ben Cartwright-Cox wrote:
> Sending ICMP packets with raw sockets ends up in the SNMP counters
> logging the type as the first byte of the IPv4 header rather than
> the ICMP header (in nearly all cases this is seen as "OutType69".
> This is fixed by adding the IP Header Length to the casting into
> a icmphdr struct.
> 
> Signed-off-by: Ben Cartwright-Cox <ben@...jojo.co.uk>
> ---
>  net/ipv4/raw.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
> index 561cd4b..1ad8bae 100644
> --- a/net/ipv4/raw.c
> +++ b/net/ipv4/raw.c
> @@ -409,7 +409,7 @@ static int raw_send_hdrinc(struct sock *sk, struct flowi4 *fl4,
>  	}
>  	if (iph->protocol == IPPROTO_ICMP)
>  		icmp_out_count(net, ((struct icmphdr *)
> -			skb_transport_header(skb))->type);
> +			skb_transport_header(skb) + iphlen)->type);
>  
>  	err = NF_HOOK(NFPROTO_IPV4, NF_INET_LOCAL_OUT, sk, skb,
>  		      NULL, rt->dst.dev, dst_output_sk);


Hmm... This seems to lack checks against a malicious user ?

The only guarantee you have here is that iphlen < length.

It is not enough.

Make sure you do not access not initialized memory or even non existent
one.



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