inet: RAW sockets using IPPROTO_RAW MUST drop incoming ICMP

Yizhou Zhao reported that simply having one RAW socket on protocol
IPPROTO_RAW (255) was dangerous.

  socket(AF_INET, SOCK_RAW, 255);

A malicious incoming ICMP packet can set the protocol field to 255
and match this socket, leading to FNHE cache changes.

inner = IP(src="192.168.2.1", dst="8.8.8.8", proto=255)/Raw("TEST")
pkt = IP(src="192.168.1.1", dst="192.168.2.1")/ICMP(type=3, code=4, nexthopmtu=576)/inner

"man 7 raw" states:

  A protocol of IPPROTO_RAW implies enabled IP_HDRINCL and is able
  to send any IP protocol that is specified in the passed header.
  Receiving of all IP protocols via IPPROTO_RAW is not possible
  using raw sockets.

Make sure we drop these malicious packets.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Reported-by: Yizhou Zhao <[email protected]>
Link: https://lore.kernel.org/netdev/[email protected]/
Signed-off-by: Eric Dumazet <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Reviewed-by: Ido Schimmel <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: edumazet

net/ipv4/icmp.c

@@ -1031,16 +1031,22 @@ static void icmp_socket_deliver(struct sk_buff *skb, u32 info)
 	/* Checkin full IP header plus 8 bytes of protocol to
 	 * avoid additional coding at protocol handlers.
 	 */
-	if (!pskb_may_pull(skb, iph->ihl * 4 + 8)) {
-		__ICMP_INC_STATS(dev_net_rcu(skb->dev), ICMP_MIB_INERRORS);
-		return;
-	}
+	if (!pskb_may_pull(skb, iph->ihl * 4 + 8))
+		goto out;
+
+	/* IPPROTO_RAW sockets are not supposed to receive anything. */
+	if (protocol == IPPROTO_RAW)
+		goto out;
 
 	raw_icmp_error(skb, protocol, info);
 
 	ipprot = rcu_dereference(inet_protos[protocol]);
 	if (ipprot && ipprot->err_handler)
 		ipprot->err_handler(skb, info);
+	return;
+
+out:
+	__ICMP_INC_STATS(dev_net_rcu(skb->dev), ICMP_MIB_INERRORS);
 }
 
 static bool icmp_tag_validation(int proto)

net/ipv6/icmp.c

@@ -1066,6 +1066,12 @@ enum skb_drop_reason icmpv6_notify(struct sk_buff *skb, u8 type,
 	if (reason != SKB_NOT_DROPPED_YET)
 		goto out;
 
+	if (nexthdr == IPPROTO_RAW) {
+		/* Add a more specific reason later ? */
+		reason = SKB_DROP_REASON_NOT_SPECIFIED;
+		goto out;
+	}
+
 	/* BUGGG_FUTURE: we should try to parse exthdrs in this packet.
 	   Without this we will not able f.e. to make source routed
 	   pmtu discovery.