Advanced ICMP options (#240)

Add payload to ICMP Probe
Add the option to send packets with DF-Bit set.

Signed-off-by: Goutham Veeramachaneni <[email protected]>

CONFIGURATION.md

@@ -168,6 +168,12 @@ validate_additional_rrs:
 # The preferred IP protocol of the ICMP probe (ip4, ip6).
 [ preferred_ip_protocol: <string> | default = "ip6" ]
 
+# Set the DF-bit in the IP-header. Only works with ip4 and on *nix systems.
+[ dont_fragment: <boolean> | default = false ]
+
+# The size of the payload.
+[ payload_size: <int> ]
+
 ```
 
 ### <tls_config>

config/config.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -96,7 +97,8 @@ type TCPProbe struct {
 
 type ICMPProbe struct {
 	PreferredIPProtocol string `yaml:"preferred_ip_protocol,omitempty"` // Defaults to "ip6".
-
+	PayloadSize         int    `yaml:"payload_size,omitempty"`
+	DontFragment        bool   `yaml:"dont_fragment,omitempty"`
 	// Catches all undefined fields and must be empty after parsing.
 	XXX map[string]interface{} `yaml:",inline"`
 }
@@ -215,6 +217,11 @@ func (s *ICMPProbe) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal((*plain)(s)); err != nil {
 		return err
 	}
+
+	if runtime.GOOS == "windows" && s.DontFragment {
+		return errors.New("\"dont_fragment\" is not supported on windows platforms")
+	}
+
 	if err := checkOverflow(s.XXX, "icmp probe"); err != nil {
 		return err
 	}

prober/icmp.go

@@ -45,7 +45,7 @@ func getICMPSequence() uint16 {
 
 func ProbeICMP(ctx context.Context, target string, module config.Module, registry *prometheus.Registry, logger log.Logger) (success bool) {
 	var (
-		socket      *icmp.PacketConn
+		socket      net.PacketConn
 		requestType icmp.Type
 		replyType   icmp.Type
 	)
@@ -62,23 +62,52 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
 	if ip.IP.To4() == nil {
 		requestType = ipv6.ICMPTypeEchoRequest
 		replyType = ipv6.ICMPTypeEchoReply
+
 		socket, err = icmp.ListenPacket("ip6:ipv6-icmp", "::")
+		if err != nil {
+			level.Error(logger).Log("msg", "Error listening to socket", "err", err)
+			return
+		}
 	} else {
 		requestType = ipv4.ICMPTypeEcho
 		replyType = ipv4.ICMPTypeEchoReply
-		socket, err = icmp.ListenPacket("ip4:icmp", "0.0.0.0")
-	}
 
-	if err != nil {
-		level.Error(logger).Log("msg", "Error listening to socket", "err", err)
-		return
+		if !module.ICMP.DontFragment {
+			socket, err = icmp.ListenPacket("ip4:icmp", "0.0.0.0")
+			if err != nil {
+				level.Error(logger).Log("msg", "Error listening to socket", "err", err)
+				return
+			}
+		} else {
+			s, err := net.ListenPacket("ip4:icmp", "0.0.0.0")
+			if err != nil {
+				level.Error(logger).Log("msg", "Error listening to socket", "err", err)
+				return
+			}
+
+			rc, err := ipv4.NewRawConn(s)
+			if err != nil {
+				level.Error(logger).Log("msg", "cannot construct raw connection", "err", err)
+				return
+			}
+			socket = &dfConn{c: rc}
+		}
 	}
+
 	defer socket.Close()
 
+	var data []byte
+	if module.ICMP.PayloadSize != 0 {
+		data = make([]byte, module.ICMP.PayloadSize)
+		copy(data, "Prometheus Blackbox Exporter")
+	} else {
+		data = []byte("Prometheus Blackbox Exporter")
+	}
+
 	body := &icmp.Echo{
 		ID:   os.Getpid() & 0xffff,
 		Seq:  int(getICMPSequence()),
-		Data: []byte("Prometheus Blackbox Exporter"),
+		Data: data,
 	}
 	level.Info(logger).Log("msg", "Creating ICMP packet", "seq", body.Seq, "id", body.ID)
 	wm := icmp.Message{
@@ -106,7 +135,7 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
 		return
 	}
 
-	rb := make([]byte, 1500)
+	rb := make([]byte, 65536)
 	if err := socket.SetReadDeadline(deadline); err != nil {
 		level.Error(logger).Log("msg", "Error setting socket deadline", "err", err)
 		return
@@ -136,3 +165,60 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
 		}
 	}
 }
+
+type dfConn struct {
+	c *ipv4.RawConn
+}
+
+func (c *dfConn) ReadFrom(b []byte) (int, net.Addr, error) {
+	h, p, _, err := c.c.ReadFrom(b)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	copy(b, p)
+	n := len(b)
+	if len(p) < len(b) {
+		n = len(p)
+	}
+	return n, &net.IPAddr{IP: h.Src}, nil
+}
+
+func (d *dfConn) WriteTo(b []byte, addr net.Addr) (int, error) {
+	ipAddr, err := net.ResolveIPAddr(addr.Network(), addr.String())
+	if err != nil {
+		return 0, err
+	}
+
+	dfHeader := &ipv4.Header{
+		Version:  ipv4.Version,
+		Len:      ipv4.HeaderLen,
+		Protocol: 1,
+		TotalLen: ipv4.HeaderLen + len(b),
+		Flags:    ipv4.DontFragment,
+		TTL:      64,
+		Dst:      ipAddr.IP,
+	}
+
+	return len(b), d.c.WriteTo(dfHeader, b, nil)
+}
+
+func (d *dfConn) Close() error {
+	return d.c.Close()
+}
+
+func (d *dfConn) LocalAddr() net.Addr {
+	return nil
+}
+
+func (d *dfConn) SetDeadline(t time.Time) error {
+	return d.c.SetDeadline(t)
+}
+
+func (d *dfConn) SetReadDeadline(t time.Time) error {
+	return d.c.SetReadDeadline(t)
+}
+
+func (d *dfConn) SetWriteDeadline(t time.Time) error {
+	return d.c.SetWriteDeadline(t)
+}