ipv4: Fix potential uninit variable access bug in __ip_make_skb()

Like commit ea30388 ("ipv6: Fix an uninit variable access bug in
__ip6_make_skb()"). icmphdr does not in skb linear region under the
scenario of SOCK_RAW socket. Access icmp_hdr(skb)->type directly will
trigger the uninit variable access bug.

Use a local variable icmp_type to carry the correct value in different
scenarios.

Fixes: 96793b4 ("[IPV4]: Add ICMPMsgStats MIB (RFC 4293)")
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Ziyang Xuan

net/ipv4/ip_output.c

@@ -1570,9 +1570,19 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
 	cork->dst = NULL;
 	skb_dst_set(skb, &rt->dst);
 
-	if (iph->protocol == IPPROTO_ICMP)
-		icmp_out_count(net, ((struct icmphdr *)
-			skb_transport_header(skb))->type);
+	if (iph->protocol == IPPROTO_ICMP) {
+		u8 icmp_type;
+
+		/* For such sockets, transhdrlen is zero when do ip_append_data(),
+		 * so icmphdr does not in skb linear region and can not get icmp_type
+		 * by icmp_hdr(skb)->type.
+		 */
+		if (sk->sk_type == SOCK_RAW && !inet_sk(sk)->hdrincl)
+			icmp_type = fl4->fl4_icmp_type;
+		else
+			icmp_type = icmp_hdr(skb)->type;
+		icmp_out_count(net, icmp_type);
+	}
 
 	ip_cork_release(cork);
 out: