netdev - [Patch net] gre: verify packet before using inner header

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Date:	Tue,  7 May 2013 16:20:50 +0800
From:	Cong Wang <amwang@...hat.com>
To:	netdev@...r.kernel.org
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Pravin B Shelar <pshelar@...ira.com>,
	"David S. Miller" <davem@...emloft.net>,
	Cong Wang <amwang@...hat.com>
Subject: [Patch net] gre: verify packet before using inner header

From: Cong Wang <amwang@...hat.com>

We use ->h_proto of the inner mac header before calling
pskb_may_pull() to verify the length of the packet.
This might not be a problem, but at least we'd better
error out as early as possible.

Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: Pravin B Shelar <pshelar@...ira.com>
Cc: David S. Miller <davem@...emloft.net>
Signed-off-by: Cong Wang <amwang@...hat.com>

---
diff --git a/net/ipv4/gre.c b/net/ipv4/gre.c
index cc22363..8a90c67 100644
--- a/net/ipv4/gre.c
+++ b/net/ipv4/gre.c
@@ -149,6 +149,9 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
 	} else
 		csum = false;
 
+	if (unlikely(!pskb_may_pull(skb, ghl)))
+		goto out;
+
 	/* setup inner skb. */
 	if (greh->protocol == htons(ETH_P_TEB)) {
 		struct ethhdr *eth = (struct ethhdr *)skb_inner_mac_header(skb);
@@ -158,9 +161,6 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
 	}
 
 	skb->encapsulation = 0;
-
-	if (unlikely(!pskb_may_pull(skb, ghl)))
-		goto out;
 	__skb_pull(skb, ghl);
 	skb_reset_mac_header(skb);
 	skb_set_network_header(skb, skb_inner_network_offset(skb));
--
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