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ssh/tailssh: replace incubator process with su instead of running su as child

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This allows the SSH_AUTH_SOCK environment variable to work inside of
su and agent forwarding to succeed.

Fixes #12467

Signed-off-by: Percy Wegmann <percy@tailscale.com>
This commit is contained in:
Percy Wegmann 2024-06-14 13:28:39 -05:00 committed by Percy Wegmann
parent 24976b5bfd
commit 730f0368d0
5 changed files with 202 additions and 51 deletions
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23
.github/workflows/ssh-integrationtest.yml vendored Normal file
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@ -0,0 +1,23 @@
# Run the ssh integration tests with `make sshintegrationtest`.
# These tests can also be running locally.
name: "ssh-integrationtest"
concurrency:
group: ${{ github.workflow }}-$${{ github.head_ref || github.run_id }}
cancel-in-progress: true
on:
pull_request:
paths:
- "ssh/**"
- "tempfork/gliderlabs/ssh/**"
- ".github/workflows/ssh-integrationtest"
jobs:
ssh-integrationtest:
runs-on: ubuntu-latest
steps:
- name: Check out code
uses: actions/checkout@v4
- name: Run SSH integration tests
run: |
make sshintegrationtest

4
Makefile
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@ -110,8 +110,8 @@ publishdevnameserver: ## Build and publish k8s-nameserver image to location spec
.PHONY: sshintegrationtest
sshintegrationtest: ## Run the SSH integration tests in various Docker containers
@GOOS=linux GOARCH=amd64 go test -tags integrationtest -c ./ssh/tailssh -o ssh/tailssh/testcontainers/tailssh.test && \
GOOS=linux GOARCH=amd64 go build -o ssh/tailssh/testcontainers/tailscaled ./cmd/tailscaled && \
@GOOS=linux GOARCH=amd64 ./tool/go test -tags integrationtest -c ./ssh/tailssh -o ssh/tailssh/testcontainers/tailssh.test && \
GOOS=linux GOARCH=amd64 ./tool/go build -o ssh/tailssh/testcontainers/tailscaled ./cmd/tailscaled && \
echo "Testing on ubuntu:focal" && docker build --build-arg="BASE=ubuntu:focal" -t ssh-ubuntu-focal ssh/tailssh/testcontainers && \
echo "Testing on ubuntu:jammy" && docker build --build-arg="BASE=ubuntu:jammy" -t ssh-ubuntu-jammy ssh/tailssh/testcontainers && \
echo "Testing on ubuntu:mantic" && docker build --build-arg="BASE=ubuntu:mantic" -t ssh-ubuntu-mantic ssh/tailssh/testcontainers && \

16
ssh/tailssh/incubator.go
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@ -400,8 +400,12 @@ func tryExecLogin(dlogf logger.Logf, ia incubatorArgs) error {
}
loginArgs := ia.loginArgs(loginCmdPath)
dlogf("logging in with %s %+v", loginCmdPath, loginArgs)
// replace the running process
return unix.Exec(loginCmdPath, loginArgs, os.Environ())
// If Exec works, the Go code will not proceed past this:
err = unix.Exec(loginCmdPath, loginArgs, os.Environ())
// If we made it here, Exec failed.
return err
}
// trySU attempts to start a login shell using su. If su is available and
@ -438,8 +442,12 @@ func trySU(dlogf logger.Logf, ia incubatorArgs) (handled bool, err error) {
}
dlogf("logging in with %s %q", su, loginArgs)
cmd := newCommand(ia.hasTTY, su, loginArgs)
return true, cmd.Run()
// If Exec works, the Go code will not proceed past this:
err = unix.Exec(su, loginArgs, os.Environ())
// If we made it here, Exec failed.
return true, err
}
// findSU attempts to find an su command which supports the -l and -c flags.

203
ssh/tailssh/tailssh_integration_test.go
View File

@ -8,14 +8,13 @@
import (
"bufio"
"bytes"
"context"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/elliptic"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/pem"
"errors"
"fmt"
"io"
"log"
@ -24,6 +23,7 @@
"net/netip"
"os"
"os/exec"
"path/filepath"
"runtime"
"strings"
"testing"
@ -34,8 +34,10 @@
"github.com/pkg/sftp"
gossh "github.com/tailscale/golang-x-crypto/ssh"
"golang.org/x/crypto/ssh"
"golang.org/x/crypto/ssh/agent"
"tailscale.com/net/tsdial"
"tailscale.com/tailcfg"
glider "tailscale.com/tempfork/gliderlabs/ssh"
"tailscale.com/types/key"
"tailscale.com/types/netmap"
"tailscale.com/util/set"
@ -300,6 +302,95 @@ func TestIntegrationSCP(t *testing.T) {
}
}
func TestSSHAgentForwarding(t *testing.T) {
debugTest.Store(true)
t.Cleanup(func() {
debugTest.Store(false)
})
// Create a client SSH key
tmpDir, err := os.MkdirTemp("", "")
if err != nil {
t.Fatal(err)
}
t.Cleanup(func() {
_ = os.RemoveAll(tmpDir)
})
pkFile := filepath.Join(tmpDir, "pk")
clientKey, clientKeyRSA := generateClientKey(t, pkFile)
// Start upstream SSH server
l, err := net.Listen("tcp", "127.0.0.1:")
if err != nil {
t.Fatalf("unable to listen for SSH: %s", err)
}
t.Cleanup(func() {
_ = l.Close()
})
// Run an SSH server that accepts connections from that client SSH key.
gs := glider.Server{
Handler: func(s glider.Session) {
io.WriteString(s, "Hello world\n")
},
PublicKeyHandler: func(ctx glider.Context, key glider.PublicKey) error {
// Note - this is not meant to be cryptographically secure, it's
// just checking that SSH agent forwarding is forwarding the right
// key.
a := key.Marshal()
b := clientKey.PublicKey().Marshal()
if !bytes.Equal(a, b) {
return errors.New("key mismatch")
}
return nil
},
}
go gs.Serve(l)
// Run tailscale SSH server and connect to it
username := "testuser"
tailscaleAddr := testServer(t, username, false) // TODO: make this false to use V2 behavior
tcl, err := ssh.Dial("tcp", tailscaleAddr, &ssh.ClientConfig{
HostKeyCallback: ssh.InsecureIgnoreHostKey(),
})
if err != nil {
t.Fatal(err)
}
t.Cleanup(func() { tcl.Close() })
s, err := tcl.NewSession()
if err != nil {
t.Fatal(err)
}
// Set up SSH agent forwarding on the client
err = agent.RequestAgentForwarding(s)
if err != nil {
t.Fatal(err)
}
keyring := agent.NewKeyring()
keyring.Add(agent.AddedKey{
PrivateKey: clientKeyRSA,
})
err = agent.ForwardToAgent(tcl, keyring)
if err != nil {
t.Fatal(err)
}
// Attempt to SSH to the upstream test server using the forwarded SSH key
// and run the "true" command.
upstreamHost, upstreamPort, err := net.SplitHostPort(l.Addr().String())
if err != nil {
t.Fatal(err)
}
o, err := s.CombinedOutput(fmt.Sprintf(`ssh -T -o StrictHostKeyChecking=no -p %s upstreamuser@%s "true"`, upstreamPort, upstreamHost))
if err != nil {
t.Fatalf("unable to call true command: %s\n%s", err, o)
}
}
func fallbackToSUAvailable() bool {
if runtime.GOOS != "linux" {
return false
@ -374,10 +465,25 @@ func (s *session) read() string {
return string(_got)
}
func testClient(t *testing.T, forceV1Behavior bool) *ssh.Client {
func testClient(t *testing.T, forceV1Behavior bool, authMethods ...ssh.AuthMethod) *ssh.Client {
t.Helper()
username := "testuser"
addr := testServer(t, username, forceV1Behavior)
cl, err := ssh.Dial("tcp", addr, &ssh.ClientConfig{
HostKeyCallback: ssh.InsecureIgnoreHostKey(),
Auth: authMethods,
})
if err != nil {
t.Fatal(err)
}
t.Cleanup(func() { cl.Close() })
return cl
}
func testServer(t *testing.T, username string, forceV1Behavior bool) string {
srv := &server{
lb: &testBackend{localUser: username, forceV1Behavior: forceV1Behavior},
logf: log.Printf,
@ -392,21 +498,15 @@ func testClient(t *testing.T, forceV1Behavior bool) *ssh.Client {
t.Cleanup(func() { l.Close() })
go func() {
conn, err := l.Accept()
if err == nil {
go srv.HandleSSHConn(&addressFakingConn{conn})
for {
conn, err := l.Accept()
if err == nil {
go srv.HandleSSHConn(&addressFakingConn{conn})
}
}
}()
cl, err := ssh.Dial("tcp", l.Addr().String(), &ssh.ClientConfig{
HostKeyCallback: ssh.InsecureIgnoreHostKey(),
})
if err != nil {
log.Fatal(err)
}
t.Cleanup(func() { cl.Close() })
return cl
return l.Addr().String()
}
func testSession(t *testing.T, forceV1Behavior bool) *session {
@ -417,7 +517,7 @@ func testSession(t *testing.T, forceV1Behavior bool) *session {
func testSessionFor(t *testing.T, cl *ssh.Client) *session {
s, err := cl.NewSession()
if err != nil {
log.Fatal(err)
t.Fatal(err)
}
t.Cleanup(func() { s.Close() })
@ -435,6 +535,31 @@ func testSessionFor(t *testing.T, cl *ssh.Client) *session {
}
}
func generateClientKey(t *testing.T, privateKeyFile string) (ssh.Signer, *rsa.PrivateKey) {
t.Helper()
priv, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
t.Fatal(err)
}
mk, err := x509.MarshalPKCS8PrivateKey(priv)
if err != nil {
t.Fatal(err)
}
privateKey := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: mk})
if privateKey == nil {
t.Fatal("failed to encoded private key")
}
err = os.WriteFile(privateKeyFile, privateKey, 0600)
if err != nil {
t.Fatal(err)
}
signer, err := ssh.ParsePrivateKey(privateKey)
if err != nil {
t.Fatal(err)
}
return signer, priv
}
// testBackend implements ipnLocalBackend
type testBackend struct {
localUser string
@ -443,33 +568,23 @@ type testBackend struct {
func (tb *testBackend) GetSSH_HostKeys() ([]gossh.Signer, error) {
var result []gossh.Signer
for _, typ := range []string{"ed25519", "ecdsa", "rsa"} {
var priv any
var err error
switch typ {
case "ed25519":
_, priv, err = ed25519.GenerateKey(rand.Reader)
case "ecdsa":
curve := elliptic.P256()
priv, err = ecdsa.GenerateKey(curve, rand.Reader)
case "rsa":
const keySize = 2048
priv, err = rsa.GenerateKey(rand.Reader, keySize)
}
if err != nil {
return nil, err
}
mk, err := x509.MarshalPKCS8PrivateKey(priv)
if err != nil {
return nil, err
}
hostKey := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: mk})
signer, err := gossh.ParsePrivateKey(hostKey)
if err != nil {
return nil, err
}
result = append(result, signer)
var priv any
var err error
const keySize = 2048
priv, err = rsa.GenerateKey(rand.Reader, keySize)
if err != nil {
return nil, err
}
mk, err := x509.MarshalPKCS8PrivateKey(priv)
if err != nil {
return nil, err
}
hostKey := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: mk})
signer, err := gossh.ParsePrivateKey(hostKey)
if err != nil {
return nil, err
}
result = append(result, signer)
return result, nil
}
@ -487,7 +602,7 @@ func (tb *testBackend) NetMap() *netmap.NetworkMap {
Rules: []*tailcfg.SSHRule{
{
Principals: []*tailcfg.SSHPrincipal{{Any: true}},
Action: &tailcfg.SSHAction{Accept: true},
Action: &tailcfg.SSHAction{Accept: true, AllowAgentForwarding: true},
SSHUsers: map[string]string{"*": tb.localUser},
},
},

7
ssh/tailssh/testcontainers/Dockerfile
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@ -20,7 +20,8 @@ COPY tailssh.test .
RUN chmod 755 tailscaled
RUN echo "First run tests normally."
# RUN echo "First run tests normally."
RUN eval `ssh-agent -s` && TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestSSHAgentForwarding
RUN rm -Rf /home/testuser
RUN TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestIntegrationSFTP
RUN rm -Rf /home/testuser
@ -30,6 +31,7 @@ RUN TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestIntegra
RUN echo "Then run tests as non-root user testuser and make sure tests still pass."
RUN chown testuser:groupone /tmp/tailscalessh.log
RUN TAILSCALED_PATH=`pwd`tailscaled eval `su -m testuser -c ssh-agent -s` && su -m testuser -c "./tailssh.test -test.v -test.run TestSSHAgentForwarding"
RUN TAILSCALED_PATH=`pwd`tailscaled su -m testuser -c "./tailssh.test -test.v -test.run TestIntegration TestDoDropPrivileges"
RUN chown root:root /tmp/tailscalessh.log
@ -42,12 +44,14 @@ RUN chmod 755 /usr/bin/login
# Simulate getenforce command
RUN printf "#!/bin/bash\necho 'Enforcing'" > /usr/bin/getenforce
RUN chmod 755 /usr/bin/getenforce
RUN eval `ssh-agent -s` && TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestSSHAgentForwarding
RUN TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestIntegration
RUN mv /tmp/login_orig /usr/bin/login
RUN rm /usr/bin/getenforce
RUN echo "Then remove the login command and make sure tests still pass."
RUN rm `which login`
RUN eval `ssh-agent -s` && TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestSSHAgentForwarding
RUN rm -Rf /home/testuser
RUN TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestIntegrationSFTP
RUN rm -Rf /home/testuser
@ -58,6 +62,7 @@ RUN TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestIntegra
RUN echo "Then remove the su command and make sure tests still pass."
RUN chown root:root /tmp/tailscalessh.log
RUN rm `which su`
RUN eval `ssh-agent -s` && TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestSSHAgentForwarding
RUN TAILSCALED_PATH=`pwd`tailscaled ./tailssh.test -test.v -test.run TestIntegration
RUN echo "Test doDropPrivileges"