ipip: validate header length in ipip_tunnel_xmit

We need the same checks introduced by commit cb9f1b783850
("ip: validate header length on virtual device xmit") for
ipip tunnel.

Fixes: cb9f1b783850b ("ip: validate header length on virtual device xmit")
Signed-off-by: Haishuang Yan <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/ipip.c

···
 	const struct iphdr  *tiph = &tunnel->parms.iph;
 	u8 ipproto;
 
+	if (!pskb_inet_may_pull(skb))
+		goto tx_error;
+
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
 		ipproto = IPPROTO_IPIP;