netdev - Re: [PATCH net] net: flow_dissector: fail on evil iph->ihl

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Date:	Sat, 2 Nov 2013 22:22:27 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, edumazet@...gle.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Petr Matousek <pmatouse@...hat.com>,
	Daniel Borkmann <dborkman@...hat.com>
Subject: Re: [PATCH net] net: flow_dissector: fail on evil iph->ihl

On Fri, Nov 01, 2013 at 03:01:10PM +0800, Jason Wang wrote:
> We don't validate iph->ihl which may lead a dead loop if we meet a IPIP
> skb whose iph->ihl is zero. Fix this by failing immediately when iph->ihl
> is evil (less than 5).
> 
> This issue were introduced by commit ec5efe7946280d1e84603389a1030ccec0a767ae
> (rps: support IPIP encapsulation).
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Petr Matousek <pmatouse@...hat.com>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: Daniel Borkmann <dborkman@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>


Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
> This patch is needed for stable.
> ---
>  net/core/flow_dissector.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 8d7d0dd..143b6fd 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -40,7 +40,7 @@ again:
>  		struct iphdr _iph;
>  ip:
>  		iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
> -		if (!iph)
> +		if (!iph || iph->ihl < 5)
>  			return false;
>  
>  		if (ip_is_fragment(iph))
> -- 
> 1.8.1.2
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