[PATCH net-2.6 v2] gre: fix improper error handling

[xeb@mail.ru]

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Fix improper protocol err_handler, current implementation is fully
unapplicable and may cause kernel crash due to double kfree_skb.

Signed-off-by: Dmitry Kozlov <xeb@mail.ru>
---

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 net/ipv4/gre.c |   21 ++++++---------------
 1 files changed, 6 insertions(+), 15 deletions(-)
 
diff --git a/net/ipv4/gre.c b/net/ipv4/gre.c
index 9dbe108..dbfc21d 100644
--- a/net/ipv4/gre.c
+++ b/net/ipv4/gre.c
@@ -15,6 +15,7 @@
 #include <linux/kmod.h>
 #include <linux/skbuff.h>
 #include <linux/in.h>
+#include <linux/ip.h>
 #include <linux/netdevice.h>
 #include <linux/spinlock.h>
 #include <net/protocol.h>
@@ -96,27 +97,17 @@ drop:
 static void gre_err(struct sk_buff *skb, u32 info)
 {
 	const struct gre_protocol *proto;
-	u8 ver;
-
-	if (!pskb_may_pull(skb, 12))
-		goto drop;
+	const struct iphdr *iph = (const struct iphdr *)skb->data;
+	u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
 
-	ver = skb->data[1]&0x7f;
 	if (ver >= GREPROTO_MAX)
-		goto drop;
+		return;
 
 	rcu_read_lock();
 	proto = rcu_dereference(gre_proto[ver]);
-	if (!proto || !proto->err_handler)
-		goto drop_unlock;
-	proto->err_handler(skb, info);
-	rcu_read_unlock();
-	return;
-
-drop_unlock:
+	if (proto && proto->err_handler)
+		proto->err_handler(skb, info);
 	rcu_read_unlock();
-drop:
-	kfree_skb(skb);
 }
 
 static const struct net_protocol net_gre_protocol = {