1 files changed, 285 insertions, 0 deletions
diff --git a/ssh/client/hostkeycallback.go b/ssh/client/hostkeycallback.go
new file mode 100644
index 0000000..7279f5e
--- /dev/null
+++ b/ssh/client/hostkeycallback.go
@@ -0,0 +1,285 @@
+package client
+
+import (
+	"bufio"
+	"dtail/logger"
+	"dtail/prompt"
+	"fmt"
+	"net"
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/knownhosts"
+)
+
+type response int
+
+const (
+	trustHost     response = iota
+	dontTrustHost response = iota
+)
+
+// Represents an unknown host.
+type unknownHost struct {
+	server     string
+	remote     net.Addr
+	key        ssh.PublicKey
+	hostLine   string
+	ipLine     string
+	responseCh chan response
+}
+
+// HostKeyCallback is a wrapper around ssh.KnownHosts so that we can add all
+// unknown hosts in a single batch to the known_hosts file.
+type HostKeyCallback struct {
+	knownHostsPath  string
+	unknownCh       chan unknownHost
+	throttleCh      chan struct{}
+	trustAllHostsCh chan struct{}
+	untrustedHosts  map[string]bool
+	mutex           sync.Mutex
+}
+
+// NewHostKeyCallback returns a new wrapper.
+func NewHostKeyCallback(knownHostsPath string, trustAllHosts bool, throttleCh chan struct{}) (*HostKeyCallback, error) {
+	// Ensure file exists
+	os.OpenFile(knownHostsPath, os.O_RDONLY|os.O_CREATE, 0666)
+
+	h := HostKeyCallback{
+		knownHostsPath:  knownHostsPath,
+		unknownCh:       make(chan unknownHost),
+		trustAllHostsCh: make(chan struct{}),
+		throttleCh:      throttleCh,
+		untrustedHosts:  make(map[string]bool),
+	}
+
+	if trustAllHosts {
+		close(h.trustAllHostsCh)
+	}
+
+	return &h, nil
+}
+
+// Wrap the host key callback.
+func (h *HostKeyCallback) Wrap() ssh.HostKeyCallback {
+	return func(server string, remote net.Addr, key ssh.PublicKey) error {
+		// Parse known_hosts file
+		knownHostsCb, err := knownhosts.New(h.knownHostsPath)
+		if err != nil {
+			// Problem parsing it
+			return err
+		}
+
+		// Check for valid entry in known_hosts file
+		err = knownHostsCb(server, remote, key)
+		if err == nil {
+			// OK
+			return nil
+		}
+
+		// Make sure that interactive user callback does not interfere with
+		// SSH connection throttler.
+		<-h.throttleCh
+		defer func() { h.throttleCh <- struct{}{} }()
+
+		unknown := unknownHost{
+			server:     server,
+			remote:     remote,
+			key:        key,
+			hostLine:   knownhosts.Line([]string{server}, key),
+			ipLine:     knownhosts.Line([]string{remote.String()}, key),
+			responseCh: make(chan response),
+		}
+
+		logger.Warn("Encountered unknown host", unknown)
+		// Notify user that there is an unknown host
+		h.unknownCh <- unknown
+
+		// Wait for user input.
+		switch <-unknown.responseCh {
+		case trustHost:
+			// End user acknowledged host key
+			return nil
+		case dontTrustHost:
+		}
+
+		h.mutex.Lock()
+		defer h.mutex.Unlock()
+		h.untrustedHosts[server] = true
+
+		return err
+	}
+}
+
+// PromptAddHosts prompts a question to the user whether unknown hosts should
+// be added to the known hosts or not.
+func (h *HostKeyCallback) PromptAddHosts(stop <-chan struct{}) {
+	var hosts []unknownHost
+
+	for {
+		// Check whether there is a unknown host
+		select {
+		case unknown := <-h.unknownCh:
+			hosts = append(hosts, unknown)
+			// Ask every 50 unknown hosts
+			if len(hosts) >= 50 {
+				h.promptAddHosts(hosts)
+				hosts = []unknownHost{}
+			}
+		case <-time.After(2 * time.Second):
+			// Or ask when after 2 seconds no new unknown hosts were added.
+			if len(hosts) > 0 {
+				h.promptAddHosts(hosts)
+				hosts = []unknownHost{}
+			}
+		case <-stop:
+			logger.Debug("Stopping goroutine prompting new hosts...")
+			return
+		}
+	}
+}
+
+func (h *HostKeyCallback) promptAddHosts(hosts []unknownHost) {
+	var servers []string
+
+	for _, host := range hosts {
+		servers = append(servers, host.server)
+	}
+
+	select {
+	case <-h.trustAllHostsCh:
+		logger.Warn("Trusting host keys of servers", servers)
+		h.trustHosts(hosts)
+		return
+	default:
+	}
+
+	question := fmt.Sprintf("Encountered %d unknown hosts: '%s'\n%s",
+		len(servers),
+		strings.Join(servers, ","),
+		"Do you want to trust these hosts?",
+	)
+
+	p := prompt.New(question)
+
+	a := prompt.Answer{
+		Long:  "yes",
+		Short: "y",
+		Callback: func() {
+			h.trustHosts(hosts)
+		},
+		EndCallback: func() {
+			logger.Info("Added hosts to known hosts file", h.knownHostsPath)
+		},
+	}
+	p.Add(a)
+
+	a = prompt.Answer{
+		Long:  "all",
+		Short: "a",
+		Callback: func() {
+			close(h.trustAllHostsCh)
+			h.trustHosts(hosts)
+		},
+		EndCallback: func() {
+			logger.Info("Added hosts to known hosts file", h.knownHostsPath)
+		},
+	}
+	p.Add(a)
+
+	a = prompt.Answer{
+		Long:  "no",
+		Short: "n",
+		Callback: func() {
+			h.dontTrustHosts(hosts)
+		},
+		EndCallback: func() {
+			logger.Info("Didn't add hosts to known hosts file", h.knownHostsPath)
+		},
+	}
+	p.Add(a)
+
+	a = prompt.Answer{
+		Long:     "details",
+		Short:    "d",
+		AskAgain: true,
+		Callback: func() {
+			for _, unknown := range hosts {
+				fmt.Println(unknown.hostLine)
+				fmt.Println(unknown.ipLine)
+			}
+		},
+	}
+	p.Add(a)
+
+	p.Ask()
+}
+
+func (h *HostKeyCallback) trustHosts(hosts []unknownHost) {
+	tmpKnownHostsPath := fmt.Sprintf("%s.tmp", h.knownHostsPath)
+
+	newFd, err := os.OpenFile(tmpKnownHostsPath, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0600)
+	if err != nil {
+		panic(fmt.Sprintf("%s: %s", tmpKnownHostsPath, err.Error()))
+	}
+	defer newFd.Close()
+
+	// Newly trusted hosts in normalized form
+	addresses := make(map[string]struct{})
+
+	// First write to new known hosts file, and keep track of addresses
+	for _, unknown := range hosts {
+		unknown.responseCh <- trustHost
+
+		// Add once as [HOSTNAME]:PORT
+		addresses[knownhosts.Normalize(unknown.server)] = struct{}{}
+		// And once as [IP]:PORT
+		addresses[knownhosts.Normalize(unknown.remote.String())] = struct{}{}
+
+		newFd.WriteString(fmt.Sprintf("%s\n", unknown.hostLine))
+		newFd.WriteString(fmt.Sprintf("%s\n", unknown.ipLine))
+	}
+
+	// Read old known hosts file, to see which are old and new entries
+	os.OpenFile(h.knownHostsPath, os.O_RDONLY|os.O_CREATE, 0666)
+	oldFd, err := os.Open(h.knownHostsPath)
+	if err != nil {
+		panic(err)
+	}
+	defer oldFd.Close()
+
+	scanner := bufio.NewScanner(oldFd)
+
+	// Now, append all still valid old entries to the new host file
+	for scanner.Scan() {
+		line := scanner.Text()
+		address := strings.SplitN(line, " ", 2)[0]
+
+		if _, ok := addresses[address]; !ok {
+			newFd.WriteString(fmt.Sprintf("%s\n", line))
+		}
+	}
+
+	// Now, replace old known hosts file
+	if err := os.Rename(tmpKnownHostsPath, h.knownHostsPath); err != nil {
+		panic(err)
+	}
+}
+
+func (h *HostKeyCallback) dontTrustHosts(hosts []unknownHost) {
+	for _, unknown := range hosts {
+		unknown.responseCh <- dontTrustHost
+	}
+}
+
+// Untrusted returns true if the host is not trusted. False otherwise.
+func (h *HostKeyCallback) Untrusted(server string) bool {
+	h.mutex.Lock()
+	defer h.mutex.Unlock()
+	_, ok := h.untrustedHosts[server]
+
+	return ok
+}