From e01bf1c83332c4653ffd30eed20a94a9c83d82b2 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Sat, 12 Apr 2008 18:49:30 -0700
Subject: net: check for underlength tap writes

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 <rusty@rustcorp.com.au>
Acked-by: Max Krasnyanskiy <maxk@qualcomm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 drivers/net/tun.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 970ec4793442..5b5d87585d91 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -286,8 +286,11 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun, struct iovec *iv,
 			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++;
-- 
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