netdev - Re: Bug in using inet

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Message-ID: <20071114111305.GA14670@2ka.mipt.ru>
Date:	Wed, 14 Nov 2007 14:13:05 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Nj A <nj_a83@...oo.fr>
Cc:	netdev@...r.kernel.org
Subject: Re: Bug in using inet_lookup ()

On Wed, Nov 14, 2007 at 09:26:18AM +0000, Nj A (nj_a83@...oo.fr) wrote:
> /* The kernel TCP hashtable */
> struct inet_hashinfo __cacheline_aligned tcp_hashinfo = {
> .lhash_lock = __RW_LOCK_UNLOCKED (tcp_hashinfo.lhash_lock),
> .lhash_users = ATOMIC_INIT (0),
> .lhash_wait = __WAIT_QUEUE_HEAD_INITIALIZER (tcp_hashinfo.lhash_wait),
> };
> ...
> struct sock *sk;
> struct sk_buff *skb;
> skb = alloc_skb (MAX_TCP_HEADER + 15, GFP_KERNEL);
> if (skb == NULL)
> printk ("%s: Unable to allocate memory \n", __FUNCTION__);
> sk = inet_lookup (&tcp_hashinfo, ip_src, src_port, ip_dst, dst_port, inet_iif (skb));
> if (!sk)
> ...
> This portion of code seems to cause the kernel to panic due to dereferencing a NULL pointer.
> Can anyone please tell me what is the error above?
> Best Regards,
 
Where exactly? Likely in inet_iif(), since it dereferences dst (routing
info), which is not presented after simple alloc_skb().
You have to setup skb correctly, check how ip_rcv() does it.

-- 
	Evgeniy Polyakov
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