linux-kernel - [PATCH] Even Batman should not dereference NULL pointers

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Message-ID: <alpine.LNX.2.00.1101132146400.11347@swampdragon.chaosbits.net>
Date:	Thu, 13 Jan 2011 21:53:38 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	b.a.t.m.a.n@...ts.open-mesh.org
cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marek Lindner <lindner_marek@...oo.de>,
	Simon Wunderlich <siwu@....tu-chemnitz.de>,
	Sven Eckelmann <sven@...fation.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH] Even Batman should not dereference NULL pointers

There's a problem in net/batman-adv/unicast.c::frag_send_skb().
dev_alloc_skb() allocates memory and may fail, thus returning NULL. If 
this happens we'll pass a NULL pointer on to skb_split() which in turn 
hands it to skb_split_inside_header() from where it gets passed to 
skb_put() that lets skb_tail_pointer() play with it and that function 
dereferences it. And thus the bat dies.

While I was at it I also moved the call to dev_alloc_skb() above the 
assignment to 'unicast_packet' since there's no reason to do that 
assignment if the memory allocation fails.

Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 unicast.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/unicast.c b/net/batman-adv/unicast.c
index dc2e28b..ee41fef 100644
--- a/net/batman-adv/unicast.c
+++ b/net/batman-adv/unicast.c
@@ -229,10 +229,12 @@ int frag_send_skb(struct sk_buff *skb, struct bat_priv *bat_priv,
 	if (!bat_priv->primary_if)
 		goto dropped;
 
-	unicast_packet = (struct unicast_packet *) skb->data;
+	frag_skb = dev_alloc_skb(data_len - (data_len / 2) + ucf_hdr_len);
+	if (!frag_skb)
+		goto dropped;
 
+	unicast_packet = (struct unicast_packet *) skb->data;
 	memcpy(&tmp_uc, unicast_packet, uc_hdr_len);
-	frag_skb = dev_alloc_skb(data_len - (data_len / 2) + ucf_hdr_len);
 	skb_split(skb, frag_skb, data_len / 2);
 
 	if (my_skb_head_push(skb, ucf_hdr_len - uc_hdr_len) < 0 ||


-- 
Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

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