Subject: [PATCH 2/2] net: check for underlength tap writes

From: Rusty Russell <[email-masked]>
Date: Sat, 5 Apr 2008 21:54:33 +1000

If the user gives a packet under 14 bytes, we'll end up reading off the end
of the skb (not oopsing, just reading off the end).

Signed-off-by: Rusty Russell <[email-masked]>

diff -r 99132ad16999 drivers/net/tun.c
--- a/drivers/net/tun.c	Sat Apr 05 21:20:32 2008 +1100
+++ b/drivers/net/tun.c	Sat Apr 05 22:47:20 2008 +1100
@@ -286,8 +286,11 @@ static __inline__ ssize_t tun_get_user(s
 			return -EFAULT;
 	}
 
-	if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV)
+	if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
 		align = NET_IP_ALIGN;
+		if (unlikely(len < ETH_HLEN))
+			return -EINVAL;
+	}
 
 	if (!(skb = alloc_skb(len + align, GFP_KERNEL))) {
 		tun->dev->stats.rx_dropped++;