netdev - Re: [PATCH] net: check the length of the data before dereferencing it

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Message-ID: <1333342467.2325.6739.camel@edumazet-glaptop>
Date:	Mon, 02 Apr 2012 06:54:27 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	David Miller <davem@...emloft.net>, kaber@...sh.net,
	pablo@...filter.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] net: check the length of the data before dereferencing
 it

On Mon, 2012-04-02 at 12:47 +0800, Changli Gao wrote:

> Got it. Thanks. FYI, the tcp options are copied to the stack before
> being parsed.
> 

What do you mean ?

code looks like :

const struct tcphdr *th = tcp_hdr(skb);
int length = (th->doff * 4) - sizeof(struct tcphdr);

ptr = (const unsigned char *)(th + 1);



Therefore ptr points somewhere in skb->head ... 



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