Check content of icmp echo reply

diff --git a/icmp.go b/icmp.go
index 93a7a3adda6172b0a84f11339a2eb4701cef62b5..fb46f66265beab1aa925979d95cb7231ad0b9d1d 100644 (file)
--- a/icmp.go
+++ b/icmp.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+       "bytes"
        "golang.org/x/net/icmp"
        "golang.org/x/net/internal/iana"
        "golang.org/x/net/ipv4"
@@ -60,6 +61,14 @@ func probeICMP(target string, w http.ResponseWriter, module Module) (success boo
                return
        }
 
+       // Reply should be the same except for the message type.
+       wm.Type = ipv4.ICMPTypeEchoReply
+       wb, err = wm.Marshal(nil)
+       if err != nil {
+               log.Errorf("Error marshalling packet for %s: %s", target, err)
+               return
+       }
+
        rb := make([]byte, 1500)
        if err := socket.SetReadDeadline(deadline); err != nil {
                log.Errorf("Error setting socket deadline for %s: %s", target, err)
@@ -78,14 +87,7 @@ func probeICMP(target string, w http.ResponseWriter, module Module) (success boo
                if peer.String() != ip.String() {
                        continue
                }
-               rm, err := icmp.ParseMessage(iana.ProtocolICMP, rb[:n])
-               if err != nil {
-                       log.Warnf("Error parsing ICMP message for %s: %s", target, err)
-                       continue
-               }
-               if rm.Type == ipv4.ICMPTypeEchoReply {
-                       // The ICMP package does not support unmarshalling
-                       // messages, so assume this is the right sequence number.
+               if bytes.Compare(rb[:n], wb) == 0 {
                        success = true
                        return
                }