Fix hostkey being too short

Modern versions of ssh refuse to connect to a server with a rsa key that
  is less than 2048 and this may change to 3072 or 4096 in the future.
  ed25519 cannot change keysize

.github/workflows/push.yml

@@ -9,21 +9,18 @@ jobs:
     name: CI
     runs-on: ubuntu-latest
     steps:
+    - uses: actions/checkout@v4
 
-    - name: Set up Go 1.x
+    - name: Set up latest stable Go
-      uses: actions/setup-go@v2
+      uses: actions/setup-go@v5
       with:
-        # Run on the latest minor release of Go 1.19:
+        go-version: 'stable'
-        go-version: ^1.19
-      id: go
-
-    - name: Check out code into the Go module directory
-      uses: actions/checkout@v2
 
     - name: Ensure all files were formatted as per gofmt
       run: |
         [ "$(gofmt -l $(find . -name '*.go') 2>&1)" = "" ]
 
-    - name: Build packages
+    - name: Build and test
       run: |
-        go install -v ./...
+        go install ./...
+        go test -v ./...

README.md

@@ -97,7 +97,7 @@ busybox: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically li
 for GNU/Linux 3.7.0, BuildID[sha1]=c9e20e9849ed0ca3c2bd058427ac31a27c008efe, stripped
 $ ln -s busybox sh
 $ tar cf breakglass.tar --dereference sh
-$ breakglass -debug_tarball_pattern=debug.tar gokrazy
+$ breakglass -debug_tarball_pattern=breakglass.tar gokrazy
 /tmp/breakglass564067692 # df -h
 Filesystem                Size      Used Available Use% Mounted on
 /dev/root                60.5M     60.5M         0 100% /

breakglass.go

@@ -5,21 +5,22 @@ package main
 import (
 	"bufio"
 	"bytes"
+	"context"
+	"crypto/ed25519"
 	"crypto/rand"
-	"crypto/rsa"
 	"crypto/x509"
-	"encoding/json"
 	"encoding/pem"
 	"flag"
 	"fmt"
 	"io/ioutil"
 	"log"
 	"net"
-	"net/http"
 	"os"
 	"strings"
 	"syscall"
 
+	"github.com/gokrazy/gokapi"
+	"github.com/gokrazy/gokapi/ondeviceapi"
 	"github.com/gokrazy/gokrazy"
 
 	"golang.org/x/crypto/ssh"
@@ -28,7 +29,7 @@ import (
 var (
 	authorizedKeysPath = flag.String("authorized_keys",
 		"/perm/breakglass.authorized_keys",
-		"path to an OpenSSH authorized_keys file")
+		"path to an OpenSSH authorized_keys file; if the value is 'ec2', fetch the SSH key(s) from the AWS IMDSv2 metadata")
 
 	hostKeyPath = flag.String("host_key",
 		"/perm/breakglass.host_key",
@@ -39,7 +40,7 @@ var (
 		"port for breakglass to listen on")
 
 	enableBanner = flag.Bool("enable_banner",
-		false,
+		true,
 		"Adds a banner to greet the user on login")
 
 	forwarding = flag.String("forward",
@@ -48,7 +49,14 @@ var (
 )
 
 func loadAuthorizedKeys(path string) (map[string]bool, error) {
-	b, err := ioutil.ReadFile(path)
+	var b []byte
+	var err error
+	switch path {
+	case "ec2":
+		b, err = loadAWSEC2SSHKeys()
+	default:
+		b, err = ioutil.ReadFile(path)
+	}
 	if err != nil {
 		return nil, err
 	}
@@ -60,15 +68,7 @@ func loadAuthorizedKeys(path string) (map[string]bool, error) {
 		if tr := strings.TrimSpace(s.Text()); tr == "" || strings.HasPrefix(tr, "#") {
 			continue
 		}
-		pubKey, comment, _, _, err := ssh.ParseAuthorizedKey(s.Bytes())
+		pubKey, _, _, _, err := ssh.ParseAuthorizedKey(s.Bytes())
-
-		// This warning can be removed once the mentioned issue is resolved
-		if keyType := pubKey.Type(); keyType == "ssh-rsa" {
-			log.Print("Warning: You added a ssh-rsa key to your authorized keys, these do currently not work.")
-			log.Print("Further information: https://github.com/gokrazy/breakglass/issues/11")
-			log.Printf("Affected key: %s [...] %s (line %d)", keyType, comment, lineNum)
-		}
-
 		if err != nil {
 			return nil, err
 		}
@@ -91,7 +91,7 @@ func loadHostKey(path string) (ssh.Signer, error) {
 }
 
 func createHostKey(path string) (ssh.Signer, error) {
-	key, err := rsa.GenerateKey(rand.Reader, 1024)
+	_, key, err := ed25519.GenerateKey(rand.Reader)
 	if err != nil {
 		return nil, err
 	}
@@ -116,40 +116,16 @@ func createHostKey(path string) (ssh.Signer, error) {
 }
 
 func buildTimestamp() (string, error) {
-	var statusReply struct {
+	cfg, err := gokapi.ConnectOnDevice()
-		BuildTimestamp string `json:"BuildTimestamp"`
-	}
-	pw, err := os.ReadFile("/etc/gokr-pw.txt")
 	if err != nil {
 		return "", err
 	}
-	port, err := os.ReadFile("/etc/http-port.txt")
+	cl := ondeviceapi.NewAPIClient(cfg)
+	res, _, err := cl.SuperviseApi.Index(context.Background())
 	if err != nil {
 		return "", err
 	}
-	req, err := http.NewRequest("GET", "http://gokrazy:"+strings.TrimSpace(string(pw))+"@localhost:"+strings.TrimSpace(string(port))+"/", nil)
+	return res.BuildTimestamp, nil
-	if err != nil {
-		return "", err
-	}
-	req.Header.Set("Content-Type", "application/json")
-
-	resp, err := http.DefaultClient.Do(req)
-	if err != nil {
-		return "", err
-	}
-	defer resp.Body.Close()
-	if got, want := resp.StatusCode, http.StatusOK; got != want {
-		b, _ := ioutil.ReadAll(resp.Body)
-		return "", fmt.Errorf("unexpected HTTP status code: got %v, want %v (body: %s)", resp.Status, want, strings.TrimSpace(string(b)))
-	}
-	b, err := ioutil.ReadAll(resp.Body)
-	if err != nil {
-		return "", err
-	}
-	if err := json.Unmarshal(b, &statusReply); err != nil {
-		return "", err
-	}
-	return statusReply.BuildTimestamp, nil
 }
 
 var motd string

breakglassaws.go

@@ -0,0 +1,84 @@
+// Code for interacting with AWS EC2.
+
+package main
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+)
+
+// getEC2MetadataToken returns an IMDSv2 token from the AWS EC2 metadata
+// server. This is needed for subsequent metadata requests, at least when
+// the VM was created in IMDSv2-required mode, as is common.
+//
+// See https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html
+func getEC2MetadataToken() (string, error) {
+	req, _ := http.NewRequest("PUT", "http://169.254.169.254/latest/api/token", nil)
+	req.Header.Add("X-aws-ec2-metadata-token-ttl-seconds", "300")
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("failed to get metadata token: %w", err)
+	}
+	defer res.Body.Close()
+	if res.StatusCode != 200 {
+		return "", fmt.Errorf("failed to get metadata token: %v", res.Status)
+	}
+	all, err := io.ReadAll(res.Body)
+	if err != nil {
+		return "", fmt.Errorf("failed to read metadata token: %w", err)
+	}
+	return strings.TrimSpace(string(all)), nil
+}
+
+// loadAWSEC2SSHKeys returns 1 or more SSH public keys from the AWS
+// EC2 metadata server and returns them concatenanted, one per line,
+// as if they were all together in an ~/.ssh/authorized_keys file.
+//
+// See https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instancedata-data-retrieval.html#instance-metadata-ex-5
+func loadAWSEC2SSHKeys() ([]byte, error) {
+	token, err := getEC2MetadataToken()
+	if err != nil {
+		return nil, err
+	}
+	var authorizedKeys bytes.Buffer
+	getKeyIndex := func(idx int) error {
+		req, _ := http.NewRequest("GET", fmt.Sprintf("http://169.254.169.254/latest/meta-data/public-keys/%d/openssh-key", idx), nil)
+		req.Header.Add("X-aws-ec2-metadata-token", token)
+		res, err := http.DefaultClient.Do(req)
+		if err != nil {
+			return err
+		}
+		defer res.Body.Close()
+		if res.StatusCode != 200 {
+			return errors.New(res.Status)
+		}
+		all, err := io.ReadAll(res.Body)
+		if err != nil {
+			return err
+		}
+		// Write out a ~/.ssh/authorized_keys -looking file,
+		// with each key on its own line.
+		fmt.Fprintf(&authorizedKeys, "%s\n", bytes.TrimSpace(all))
+		return nil
+	}
+	for i := 0; ; i++ {
+		err := getKeyIndex(i)
+		if err == nil {
+			continue
+		}
+		if i == 0 {
+			// We expect at least one SSH key (index 0) if the
+			// use requested this mode, so return an error if the
+			// first one fails.
+			return nil, err
+		}
+		// But on subsequent errors, just assume we've hit the end.
+		// This is a little lazy.
+		break
+	}
+	return authorizedKeys.Bytes(), nil
+}

busybox.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+	"syscall"
+)
+
+const wellKnownBusybox = "/usr/local/bin/busybox"
+
+// mountBin bind-mounts /bin to a tmpfs.
+func mountBin() error {
+	b, err := os.ReadFile("/proc/self/mountinfo")
+	if err != nil {
+		return err
+	}
+	for _, line := range strings.Split(strings.TrimSpace(string(b)), "\n") {
+		parts := strings.Fields(line)
+		if len(parts) < 5 {
+			continue
+		}
+		mountpoint := parts[4]
+		log.Printf("Found mountpoint %q", parts[4])
+		if mountpoint == "/bin" {
+			log.Printf("/bin file system already mounted, nothing to do")
+			return nil
+		}
+	}
+
+	if err := syscall.Mount("tmpfs", "/bin", "tmpfs", 0, ""); err != nil {
+		return fmt.Errorf("mounting tmpfs on /bin: %v", err)
+	}
+
+	return nil
+}
+
+func installBusybox() error {
+	// /bin is read-only by default, so mount a tmpfs over it
+	if err := mountBin(); err != nil {
+		return err
+	}
+
+	install := exec.Command(wellKnownBusybox, "--install", "-s", "/bin")
+	install.Stdout = os.Stdout
+	install.Stderr = os.Stderr
+	if err := install.Run(); err != nil {
+		return fmt.Errorf("%v: %v", install.Args, err)
+	}
+	return nil
+}

cmd/breakglass/breakglass.go

@@ -26,7 +26,6 @@ import (
 	"github.com/gokrazy/internal/config"
 	"github.com/gokrazy/internal/httpclient"
 	"github.com/gokrazy/internal/instanceflag"
-	"github.com/gokrazy/internal/tlsflag"
 	"github.com/gokrazy/internal/updateflag"
 )
 
@@ -35,9 +34,11 @@ type bg struct {
 	cfg          *config.Struct
 	forceRestart bool
 	sshConfig    string
+	insecure     bool
 
 	// state
 	GOARCH string
+	update updateflag.Value
 }
 
 func (bg *bg) startBreakglass() error {
@@ -46,35 +47,26 @@ func (bg *bg) startBreakglass() error {
 		return err
 	}
 
-	updateHttpClient, foundMatchingCertificate, updateBaseURL, err := httpclient.For(bg.cfg)
+	updateHttpClient, _, updateBaseURL, err := httpclient.For(bg.update, bg.cfg)
 	if err != nil {
 		return err
 	}
 	updateHttpClient.Jar = jar
 
-	remoteScheme, err := httpclient.GetRemoteScheme(updateBaseURL)
-	if remoteScheme == "https" && !tlsflag.Insecure() {
-		updateBaseURL.Scheme = "https"
-		updateflag.SetUpdate(updateBaseURL.String())
-	}
-
-	if updateBaseURL.Scheme != "https" && foundMatchingCertificate {
-		fmt.Printf("\n")
-		fmt.Printf("!!!WARNING!!! Possible SSL-Stripping detected!\n")
-		fmt.Printf("Found certificate for hostname in your client configuration but the host does not offer https!\n")
-		fmt.Printf("\n")
-		if !tlsflag.Insecure() {
-			log.Fatalf("update canceled: TLS certificate found, but negotiating a TLS connection with the target failed")
-		}
-		fmt.Printf("Proceeding anyway as requested (-insecure).\n")
-	}
-
-	if err != nil {
-		return err
-	}
-
 	form, err := updateHttpClient.Get(updateBaseURL.String() + "status?path=/user/breakglass")
 	if err != nil {
+		if updateBaseURL.Scheme == "https" && bg.insecure {
+			// Try falling back to HTTP
+			bg.cfg.Update.UseTLS = "off"
+			updateHttpClient, _, updateBaseURL, err = httpclient.For(bg.update, bg.cfg)
+			if err != nil {
+				return err
+			}
+			form, err = updateHttpClient.Get(updateBaseURL.String() + "status?path=/user/breakglass")
+			if err != nil {
+				return err
+			}
+		}
 		return err
 	}
 	if form.StatusCode == http.StatusNotFound {
@@ -198,6 +190,11 @@ func breakglass() error {
 			false,
 			"prepare the SSH connection only, but do not execute SSH (useful for using breakglass within an SSH ProxyCommand)")
 
+		insecure = flag.Bool(
+			"insecure",
+			false,
+			"Fall back to HTTP if HTTPS is configured, but does not work.")
+
 		proxy = flag.Bool(
 			"proxy",
 			false,
@@ -209,13 +206,6 @@ func breakglass() error {
 			"an alternative per-user configuration file for ssh and scp")
 	)
 
-	// TODO: remove the -tls and -gokrazy_url flags after 2023-June (half a year
-	// after the introduction of instance centric config), so that we can then
-	// merge these flags into tools/internal/oldpacker and remove their global
-	// state.
-	tlsflag.RegisterFlags(flag.CommandLine)
-	updateflag.RegisterFlags(flag.CommandLine, "gokrazy_url")
-
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "Usage of %s:\n\n", os.Args[0])
 
@@ -231,17 +221,10 @@ func breakglass() error {
 		log.Fatalf("syntax: breakglass <hostname> [command]")
 	}
 
-	// If the user did not explicitly specify -update=yes, we default to it.
-	// This differs from the gokr-packer, but breakglass is only useful for
-	// gokrazy instances that already exist.
-	if updateflag.NewInstallation() {
-		updateflag.SetUpdate("yes")
-	}
-
 	instance := flag.Arg(0)
 	instanceflag.SetInstance(instance)
 
-	cfg, err := config.ReadFromFile()
+	cfg, err := config.ApplyInstanceFlag()
 	if err != nil {
 		if os.IsNotExist(err) {
 			// best-effort compatibility for old setups
@@ -255,6 +238,8 @@ func breakglass() error {
 		cfg:          cfg,
 		forceRestart: *forceRestart,
 		sshConfig:    *sshConfig,
+		insecure:     *insecure,
+		update:       updateflag.Value{Update: "yes"},
 	}
 	if cfg.Update.Hostname == "" {
 		cfg.Update.Hostname = cfg.Hostname

go.mod

@@ -1,22 +1,24 @@
 module github.com/gokrazy/breakglass
 
-go 1.19
+go 1.24.0
 
 require (
-	github.com/gokrazy/gokrazy v0.0.0-20211024151958-b718dd90ae71
+	github.com/gokrazy/gokapi v0.0.0-20250222071133-506fdb322775
-	github.com/gokrazy/internal v0.0.0-20230117180442-8b3fd7aed8bb
+	github.com/gokrazy/gokrazy v0.0.0-20250222061409-bd0bb5f1d0b5
+	github.com/gokrazy/internal v0.0.0-20251208203110-3c1aa9087c82
 	github.com/google/renameio/v2 v2.0.0
-	github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf
+	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
 	github.com/kr/pty v1.1.8
-	github.com/pkg/sftp v1.13.5-0.20220330091711-a17a626ab843
+	github.com/pkg/sftp v1.13.5
-	golang.org/x/crypto v0.1.0
+	golang.org/x/crypto v0.45.0
 )
 
 require (
-	github.com/creack/pty v1.1.7 // indirect
+	github.com/creack/pty v1.1.18 // indirect
+	github.com/kenshaw/evdev v0.1.0 // indirect
 	github.com/kr/fs v0.1.0 // indirect
-	github.com/mdlayher/watchdog v0.0.0-20201005150459-8bdc4f41966b // indirect
+	github.com/mdlayher/watchdog v0.0.0-20221003142519-49be0df7b3b5 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
-	golang.org/x/sys v0.1.0 // indirect
+	golang.org/x/oauth2 v0.27.0 // indirect
-	rsc.io/goversion v1.2.0 // indirect
+	golang.org/x/sys v0.38.0 // indirect
 )

go.sum

@@ -1,61 +1,54 @@
-github.com/anatol/vmtest v0.0.0-20210623221036-69fc760fbd4b/go.mod h1:l08qtd2JHjoYWIROnbKoKCUqIbe54ndrXwDdyiDfq30=
-github.com/beevik/ntp v0.2.0/go.mod h1:hIHWr+l3+/clUnF44zdK+CWW7fO8dR5cIylAQ76NRpg=
-github.com/creack/pty v1.1.7 h1:6pwm8kMQKCmgUg0ZHTm5+/YvRK0s3THD/28+T6/kk4A=
 github.com/creack/pty v1.1.7/go.mod h1:lj5s0c3V2DBrqTV7llrYr5NG6My20zk30Fl46Y7DoTY=
+github.com/creack/pty v1.1.18 h1:n56/Zwd5o6whRC5PMGretI4IdRLlmBXYNjScPaBgsbY=
+github.com/creack/pty v1.1.18/go.mod h1:MOBLtS5ELjhRRrroQr9kyvTxUAFNvYEK993ew/Vr4O4=
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/gokrazy/gokrazy v0.0.0-20211024151958-b718dd90ae71 h1:NHLkr4NYMY9gZGTI+jzIo38ZffMHkPbBzMcUDkyHs0g=
+github.com/gokrazy/gokapi v0.0.0-20250222071133-506fdb322775 h1:f5+2UMRRbr3+e/gdWCBNn48chS/KMMljfbmlSSHfRBA=
-github.com/gokrazy/gokrazy v0.0.0-20211024151958-b718dd90ae71/go.mod h1:eq2ROPhZJtxxEi21P8cbNqP8pwRBSpW/4LGKwNiQg2Y=
+github.com/gokrazy/gokapi v0.0.0-20250222071133-506fdb322775/go.mod h1:q9mIV8al0wqmqFXJhKiO3SOHkL9/7Q4kIMynqUQWhgU=
-github.com/gokrazy/internal v0.0.0-20210621162516-1b3b5687a06d/go.mod h1:Gqv1x1DNrObmBvVvblpZbvZizZ0dU5PwiwYHipmtY9Y=
+github.com/gokrazy/gokrazy v0.0.0-20250222061409-bd0bb5f1d0b5 h1:VQhDGxRliP4ZTQ8+33v4VKtOpX4VzN8pA4zBMZQSSxs=
-github.com/gokrazy/internal v0.0.0-20230117180442-8b3fd7aed8bb h1:MT59ew5neGiU6hqFOnlqwo6pavSpdX1JUgBOvzDjNec=
+github.com/gokrazy/gokrazy v0.0.0-20250222061409-bd0bb5f1d0b5/go.mod h1:6fAh0J7aH6o5HWSiwN6uxNlm6Rjx1BxeNMWyNBQZ6sI=
-github.com/gokrazy/internal v0.0.0-20230117180442-8b3fd7aed8bb/go.mod h1:ddHcxXZ/VVQOSAWcRBbkYY58+QOw4L145ye6phyDmRA=
+github.com/gokrazy/internal v0.0.0-20251208203110-3c1aa9087c82 h1:4ghNfD9NaZLpFrqQiBF6mPVFeMYXJSky38ubVA4ic2E=
-github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/gokrazy/internal v0.0.0-20251208203110-3c1aa9087c82/go.mod h1:dQY4EMkD4L5ZjYJ0SPtpgYbV7MIUMCxNIXiOfnZ6jP4=
 github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
-github.com/google/gopacket v1.1.16/go.mod h1:UCLx9mCmAwsVbn6qQl1WIEt2SO7Nd2fD0th1TBAsqBw=
+github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/renameio/v2 v2.0.0 h1:UifI23ZTGY8Tt29JbYFiuyIU3eX+RNFtUwefq9qAhxg=
 github.com/google/renameio/v2 v2.0.0/go.mod h1:BtmJXm5YlszgC+TD4HOEEUFgkJP3nLxehU6hfe7jRt4=
-github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf h1:7+FW5aGwISbqUtkfmIpZJGRgNFg2ioYPvFaUxdqpDsg=
+github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 h1:El6M4kTTCOh6aBiKaUGG7oYTSPP8MxqL4YI3kZKwcP4=
-github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf/go.mod h1:RpwtwJQFrIEPstU94h88MWPXP2ektJZ8cZ0YntAmXiE=
+github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510/go.mod h1:pupxD2MaaD3pAXIBCelhxNneeOaAeabZDe5s4K6zSpQ=
+github.com/kenshaw/evdev v0.1.0 h1:wmtceEOFfilChgdNT+c/djPJ2JineVsQ0N14kGzFRUo=
+github.com/kenshaw/evdev v0.1.0/go.mod h1:B/fErKCihUyEobz0mjn2qQbHgyJKFQAxkXSvkeeA/Wo=
 github.com/kr/fs v0.1.0 h1:Jskdu9ieNAYnjxsi0LbQp1ulIKZV1LAFgK1tWhpZgl8=
 github.com/kr/fs v0.1.0/go.mod h1:FFnZGqtBN9Gxj7eW1uZ42v5BccTP0vu6NEaFoC2HwRg=
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ssh.go

@@ -215,6 +215,16 @@ type exitStatus struct {
 }
 
 func findShell() string {
+	if _, err := os.Stat(wellKnownBusybox); err == nil {
+		// Install busybox to /bin to provide the typical userspace utilities
+		// in standard locations (makes Emacs TRAMP work, for example).
+		if err := installBusybox(); err != nil {
+			log.Printf("installing busybox failed: %v", err)
+			// fallthrough
+		} else {
+			return "/bin/sh" // available after installation
+		}
+	}
 	if path, err := exec.LookPath("sh"); err == nil {
 		return path
 	}