From mboxrd@z Thu Jan  1 00:00:00 1970
From: Roel Kluin <roel.kluin@gmail.com>
Subject: Re: [PATCH] [IPV4]: Buffer overflow
Date: Thu, 30 Jul 2009 11:46:59 +0200
Message-ID: <4A716C13.6030208@gmail.com>
References: <4A702A02.30509@gmail.com> <4A70C6FF.9060302@gmail.com>
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Cc: "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
To: Jarek Poplawski <jarkao2@gmail.com>
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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@gmail.com>
---
Op 30-07-09 00:02, Jarek Poplawski schreef:
> Roel Kluin wrote, On 07/29/2009 12:52 PM:

>> -	hbuffer[--k] = 0;
>> +	if (k != 0)
>> +		hbuffer[--k] = 0;
> 
> 
> I guess for k == 0 we need hbuffer[0] = 0 too.
> 
> Jarek P.

Thanks, updated patch below.

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index c29d75d..090e999 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1304,7 +1304,9 @@ 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)
+		--k;
+	hbuffer[k] = 0;
 #if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
 	}
 #endif