mugit/internal/ssh/ssh.go (view raw)
Oleksandr Smirnov
Oleksandr Smirnov
olexsmir@gmail.com ssh: make sure there's no shell injections with SSH_ORIGINAL_COMMAND, 1 month ago
olexsmir@gmail.com ssh: make sure there's no shell injections with SSH_ORIGINAL_COMMAND, 1 month ago
| 1 | package ssh |
| 2 | |
| 3 | import ( |
| 4 | "context" |
| 5 | "errors" |
| 6 | "fmt" |
| 7 | "io" |
| 8 | "strings" |
| 9 | |
| 10 | "olexsmir.xyz/mugit/internal/config" |
| 11 | "olexsmir.xyz/mugit/internal/git" |
| 12 | |
| 13 | gossh "golang.org/x/crypto/ssh" |
| 14 | ) |
| 15 | |
| 16 | type Shell struct { |
| 17 | cfg *config.Config |
| 18 | |
| 19 | keys []gossh.PublicKey |
| 20 | } |
| 21 | |
| 22 | func NewShell(cfg *config.Config) (*Shell, error) { |
| 23 | parsedKeys := make([]gossh.PublicKey, len(cfg.SSH.Keys)) |
| 24 | for i, key := range cfg.SSH.Keys { |
| 25 | pkey, _, _, _, err := gossh.ParseAuthorizedKey([]byte(key)) |
| 26 | if err != nil { |
| 27 | return nil, err |
| 28 | } |
| 29 | parsedKeys[i] = pkey |
| 30 | } |
| 31 | |
| 32 | return &Shell{ |
| 33 | cfg: cfg, |
| 34 | keys: parsedKeys, |
| 35 | }, nil |
| 36 | } |
| 37 | |
| 38 | func (s *Shell) HandleCommand(ctx context.Context, cmd string, stdin io.Reader, stdout, stderr io.Writer) error { |
| 39 | gitCmd, repoName, err := s.parseCommand(cmd) |
| 40 | if err != nil { |
| 41 | return s.replyWithGitError(stderr, "access denied: invalid command", err) |
| 42 | } |
| 43 | |
| 44 | repoPath, err := git.ResolvePath(s.cfg.Repo.Dir, git.ResolveName(repoName)) |
| 45 | if err != nil { |
| 46 | return s.replyWithGitError(stderr, "access denied", err) |
| 47 | } |
| 48 | |
| 49 | repo, err := git.Open(repoPath, "") |
| 50 | if err != nil { |
| 51 | if !errors.Is(err, git.ErrRepoNotFound) || gitCmd != "git-receive-pack" { |
| 52 | return s.replyWithGitError(stderr, "repository not found", err) |
| 53 | } |
| 54 | |
| 55 | // SSH Git clients display informational messages from stderr; stdout must remain protocol-only for git-receive-pack. |
| 56 | if ierr := s.replyWithGitInfo(stderr, "auto-initializing "+repoName); ierr != nil { |
| 57 | return ierr |
| 58 | } |
| 59 | |
| 60 | if ierr := git.Init(repoPath); ierr != nil { |
| 61 | return s.replyWithGitError(stderr, "failed to init repo", ierr) |
| 62 | } |
| 63 | |
| 64 | repo, err = git.Open(repoPath, "") |
| 65 | if err != nil { |
| 66 | return s.replyWithGitError(stderr, "failed to open initialized repo", err) |
| 67 | } |
| 68 | } |
| 69 | |
| 70 | switch gitCmd { |
| 71 | case "git-upload-pack": |
| 72 | err = repo.UploadPack(ctx, false, "", stdin, stdout) |
| 73 | case "git-upload-archive": |
| 74 | err = repo.UploadArchive(ctx, stdin, stdout) |
| 75 | case "git-receive-pack": |
| 76 | err = repo.ReceivePack(ctx, stdin, stdout, stderr) |
| 77 | default: |
| 78 | msg := "access denied: invalid git command" |
| 79 | return s.replyWithGitError(stderr, msg, errors.New(msg)) |
| 80 | } |
| 81 | |
| 82 | if err != nil { |
| 83 | return err |
| 84 | } |
| 85 | |
| 86 | return nil |
| 87 | } |
| 88 | |
| 89 | func (s *Shell) AuthorizedKeys(executablePath string) string { |
| 90 | var out strings.Builder |
| 91 | for _, key := range s.cfg.SSH.Keys { |
| 92 | fmt.Fprintf(&out, `command="%s shell",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty %s`+"\n", |
| 93 | executablePath, key) |
| 94 | } |
| 95 | return out.String() |
| 96 | } |
| 97 | |
| 98 | var validCommands = map[string]bool{ |
| 99 | "git-upload-pack": true, |
| 100 | "git-upload-archive": true, |
| 101 | "git-receive-pack": true, |
| 102 | } |
| 103 | |
| 104 | func (s *Shell) parseCommand(cmd string) (gitCmd, repoName string, err error) { |
| 105 | cmdParts := strings.Fields(cmd) |
| 106 | if len(cmdParts) != 2 { |
| 107 | return "", "", fmt.Errorf("invalid command: expected 'git-cmd repo', got %q", cmd) |
| 108 | } |
| 109 | |
| 110 | gitCmd = cmdParts[0] |
| 111 | if !validCommands[gitCmd] { |
| 112 | return "", "", fmt.Errorf("invalid command: disallowed command") |
| 113 | } |
| 114 | |
| 115 | repoName = strings.Trim(cmdParts[1], "'\"") |
| 116 | if repoName == "" { |
| 117 | return "", "", fmt.Errorf("invalid command: empty repository name") |
| 118 | } |
| 119 | |
| 120 | return gitCmd, repoName, nil |
| 121 | } |
| 122 | |
| 123 | func (s *Shell) replyWithGitError(stderr io.Writer, msg string, cause error) error { |
| 124 | if _, err := fmt.Fprintf(stderr, "error: %s\n", msg); err != nil { |
| 125 | return err |
| 126 | } |
| 127 | |
| 128 | return cause |
| 129 | } |
| 130 | |
| 131 | func (s *Shell) replyWithGitInfo(msgOut io.Writer, msg string) error { |
| 132 | _, err := fmt.Fprintf(msgOut, "info: %s\n", msg) |
| 133 | return err |
| 134 | } |