Re: [SECURITY] CERT/CC VU#464113, SYN plus RST/FIN

[Alex Riesen]

On Fri, Oct 25, 2002 at 11:00:43AM +0200, Florian Weimer wrote:
> This patch prevents SYN+RST and SYN+FIN segments which arrive in the
> LISTEN state from initiating a three-way handshake.
> 
> I'm not sure if it is correct, but it's better than nothing (so far, I
> haven't seen any patch for this issue).
> 
> --- tcp_input.c	2002/10/25 08:45:20	1.1
> +++ tcp_input.c	2002/10/25 08:49:21
> @@ -3668,6 +3668,8 @@
>  	case TCP_LISTEN:
>  		if(th->ack)
>  			return 1;
> +		if(th->rst || th->fin)
> +			goto discard;
>  
>  		if(th->syn) {
>  			if(tp->af_specific->conn_request(sk, skb) < 0)
> 

You mean to place the check below "if(th->syn)", don't you?

-alex