net: icmpv4: Drop ICMPv4 packet if ICMP header is NULL

This commit fixes the crash of echo_server from malformed
ICMPv4 packet.

Fixes #6081

Signed-off-by: Ruslan Mstoi <[email protected]>

Author: Ruslan Mstoi

subsys/net/ip/ipv4.c

@@ -142,6 +142,10 @@ static inline enum net_verdict process_icmpv4_pkt(struct net_pkt *pkt,
 	struct net_icmp_hdr hdr, *icmp_hdr;
 
 	icmp_hdr = net_icmpv4_get_hdr(pkt, &hdr);
+	if (!icmp_hdr) {
+		NET_DBG("NULL ICMPv4 header - dropping");
+		return NET_DROP;
+	}
 
 	NET_DBG("ICMPv4 packet received type %d code %d",
 		icmp_hdr->type, icmp_hdr->code);