From c611d8480bb4a7af35afff3d61ad48168de0d8d6 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Thu, 28 Jan 2021 15:29:17 -0800
Subject: [PATCH] cmd/tailscaled: add whois/identd-ish debug handler

---
 ipn/ipnserver/server.go | 40 +++++++++++++++++++++++++++++++++
 ipn/local.go            | 49 +++++++++++++++++++++++++++++++++++++++++
 tailcfg/tailcfg.go      |  6 +++++
 3 files changed, 95 insertions(+)

diff --git a/ipn/ipnserver/server.go b/ipn/ipnserver/server.go
index 7518c6e2a..69d160d52 100644
--- a/ipn/ipnserver/server.go
+++ b/ipn/ipnserver/server.go
@@ -7,6 +7,7 @@ package ipnserver
 import (
 	"bufio"
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -32,6 +33,7 @@ import (
 	"tailscale.com/net/netstat"
 	"tailscale.com/safesocket"
 	"tailscale.com/smallzstd"
+	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/pidowner"
 	"tailscale.com/util/systemd"
@@ -620,6 +622,7 @@ func Run(ctx context.Context, logf logger.Logf, logid string, getEngine func() (
 		opts.DebugMux.HandleFunc("/debug/ipn", func(w http.ResponseWriter, r *http.Request) {
 			serveHTMLStatus(w, b)
 		})
+		opts.DebugMux.Handle("/whois", whoIsHandler{b})
 	}
 
 	server.b = b
@@ -883,3 +886,40 @@ func peerPid(entries []netstat.Entry, la, ra netaddr.IPPort) int {
 	}
 	return 0
 }
+
+// whoIsHandler is the debug server's /debug?ip=$IP HTTP handler.
+type whoIsHandler struct {
+	b *ipn.LocalBackend
+}
+
+func (h whoIsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	b := h.b
+	var ip netaddr.IP
+	if v := r.FormValue("ip"); v != "" {
+		var err error
+		ip, err = netaddr.ParseIP(r.FormValue("ip"))
+		if err != nil {
+			http.Error(w, "invalid 'ip' parameter", 400)
+			return
+		}
+	} else {
+		http.Error(w, "missing 'ip' parameter", 400)
+		return
+	}
+	n, u, ok := b.WhoIs(ip)
+	if !ok {
+		http.Error(w, "no match for IP", 404)
+		return
+	}
+	res := &tailcfg.WhoIsResponse{
+		Node:        n,
+		UserProfile: &u,
+	}
+	j, err := json.MarshalIndent(res, "", "\t")
+	if err != nil {
+		http.Error(w, "JSON encoding error", 500)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	w.Write(j)
+}
diff --git a/ipn/local.go b/ipn/local.go
index 580c49abc..335be2244 100644
--- a/ipn/local.go
+++ b/ipn/local.go
@@ -90,6 +90,7 @@ type LocalBackend struct {
 	hostinfo *tailcfg.Hostinfo
 	// netMap is not mutated in-place once set.
 	netMap       *controlclient.NetworkMap
+	nodeByAddr   map[netaddr.IP]*tailcfg.Node
 	activeLogin  string // last logged LoginName from netMap
 	engineStatus EngineStatus
 	endpoints    []string
@@ -234,7 +235,22 @@ func (b *LocalBackend) UpdateStatus(sb *ipnstate.StatusBuilder) {
 			})
 		}
 	}
+}
 
+// WhoIs reports the node and user who owns the node with the given IP.
+// If ok == true, n and u are valid.
+func (b *LocalBackend) WhoIs(ip netaddr.IP) (n *tailcfg.Node, u tailcfg.UserProfile, ok bool) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	n, ok = b.nodeByAddr[ip]
+	if !ok {
+		return nil, u, false
+	}
+	u, ok = b.netMap.UserProfiles[n.User]
+	if !ok {
+		return nil, u, false
+	}
+	return n, u, true
 }
 
 // SetDecompressor sets a decompression function, which must be a zstd
@@ -1507,6 +1523,39 @@ func (b *LocalBackend) setNetMapLocked(nm *controlclient.NetworkMap) {
 		b.logf("active login: %v", login)
 		b.activeLogin = login
 	}
+
+	if nm == nil {
+		b.nodeByAddr = nil
+		return
+	}
+
+	// Update the nodeByAddr index.
+	if b.nodeByAddr == nil {
+		b.nodeByAddr = map[netaddr.IP]*tailcfg.Node{}
+	}
+	// First pass, mark everything unwanted.
+	for k := range b.nodeByAddr {
+		b.nodeByAddr[k] = nil
+	}
+	addNode := func(n *tailcfg.Node) {
+		for _, ipp := range n.Addresses {
+			if ipp.IsSingleIP() {
+				b.nodeByAddr[ipp.IP] = n
+			}
+		}
+	}
+	if nm.SelfNode != nil {
+		addNode(nm.SelfNode)
+	}
+	for _, p := range nm.Peers {
+		addNode(p)
+	}
+	// Third pass, actually delete the unwanted items.
+	for k, v := range b.nodeByAddr {
+		if v == nil {
+			delete(b.nodeByAddr, k)
+		}
+	}
 }
 
 // TestOnlyPublicKeys returns the current machine and node public
diff --git a/tailcfg/tailcfg.go b/tailcfg/tailcfg.go
index 4e7c51f79..ba215000e 100644
--- a/tailcfg/tailcfg.go
+++ b/tailcfg/tailcfg.go
@@ -935,3 +935,9 @@ func eqCIDRs(a, b []netaddr.IPPrefix) bool {
 func eqTimePtr(a, b *time.Time) bool {
 	return ((a == nil) == (b == nil)) && (a == nil || a.Equal(*b))
 }
+
+// WhoIsResponse is the JSON type returned by tailscaled debug server's /whois?ip=$IP handler.
+type WhoIsResponse struct {
+	Node        *Node
+	UserProfile *UserProfile
+}