ping: discard packets with wrong source address

RFC 1122 clearly states that the IP address in the reply MUST match the
one in the request:

	The IP source address in an ICMP Echo Reply MUST be the same
	as the specific-destination address (defined in Section
	3.2.1.3) of the corresponding ICMP Echo Request message.

This is not enforced in iputils neither in IPv4 nor in IPv6:

	$ ping -c4 127.0.0.1
	PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
	64 bytes from 127.0.0.5: icmp_seq=1 ttl=64 time=0.072 ms
	64 bytes from 127.0.0.5: icmp_seq=2 ttl=64 time=0.101 ms
	64 bytes from 127.0.0.5: icmp_seq=3 ttl=64 time=0.079 ms
	64 bytes from 127.0.0.5: icmp_seq=4 ttl=64 time=0.081 ms

	--- 127.0.0.1 ping statistics ---
	4 packets transmitted, 4 received, 0% packet loss, time 3056ms
	rtt min/avg/max/mdev = 0.072/0.083/0.101/0.010 ms

	$ ping -c4 ::1
	PING ::1(::1) 56 data bytes
	64 bytes from ::5: icmp_seq=1 ttl=64 time=0.029 ms
	64 bytes from ::5: icmp_seq=2 ttl=64 time=0.084 ms
	64 bytes from ::5: icmp_seq=3 ttl=64 time=0.064 ms
	64 bytes from ::5: icmp_seq=4 ttl=64 time=0.083 ms

	--- ::1 ping statistics ---
	4 packets transmitted, 4 received, 0% packet loss, time 3074ms
	rtt min/avg/max/mdev = 0.029/0.065/0.084/0.022 ms

The same issue happens both with raw and ICMP sockets.

Signed-off-by: Matteo Croce <[email protected]>

ping/ping.c

@@ -1538,6 +1538,9 @@ int ping4_parse_reply(struct ping_rts *rts, struct socket_st *sock,
 	csfailed = in_cksum((unsigned short *)icp, cc, 0);
 
 	if (icp->type == ICMP_ECHOREPLY) {
+		if (!rts->broadcast_pings && !rts->multicast &&
+		    from->sin_addr.s_addr != rts->whereto.sin_addr.s_addr)
+			return 1;
 		if (!is_ours(rts, sock, icp->un.echo.id))
 			return 1;			/* 'Twas not our ECHO */
 		if (!contains_pattern_in_payload(rts, (uint8_t *)(icp + 1)))

ping/ping6_common.c

@@ -815,6 +815,9 @@ int ping6_parse_reply(struct ping_rts *rts, socket_st *sock,
 	}
 
 	if (icmph->icmp6_type == ICMP6_ECHO_REPLY) {
+		if (!rts->multicast &&
+		    memcmp(&from->sin6_addr.s6_addr, &rts->whereto6.sin6_addr.s6_addr, 16))
+			return 1;
 		if (!is_ours(rts, sock, icmph->icmp6_id))
 			return 1;
 	       if (!contains_pattern_in_payload(rts, (uint8_t *)(icmph + 1)))