netdev - Re: [PATCH] [IPV4]: Buffer overflow

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Date:	Thu, 30 Jul 2009 00:02:39 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Roel Kluin <roel.kluin@...il.com>
CC:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] [IPV4]: Buffer overflow

Roel Kluin wrote, On 07/29/2009 12:52 PM:

> If arp_format_neigh_entry() can be called with n->dev->addr_len == 0, then a
> write to hbuffer[-1] occurs.
> 
> Signed-off-by: Roel Kluin <roel.kluin@...il.com>
> ---
> Found with Parfait, http://research.sun.com/projects/parfait/
> 
> It's not clear whether this can happen or not.
> 
> diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
> index c29d75d..252336f 100644
> --- a/net/ipv4/arp.c
> +++ b/net/ipv4/arp.c
> @@ -1304,7 +1304,8 @@ static void arp_format_neigh_entry(struct seq_file *seq,
>  		hbuffer[k++] = hex_asc_lo(n->ha[j]);
>  		hbuffer[k++] = ':';
>  	}
> -	hbuffer[--k] = 0;
> +	if (k != 0)
> +		hbuffer[--k] = 0;


I guess for k == 0 we need hbuffer[0] = 0 too.

Jarek P.

>  #if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
>  	}
>  #endif
> --
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