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>

1 files changed, 4 insertions, 1 deletions

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++;