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import ( "context" "fmt" "log/slog" "net/http" "net/url" "os" "os/exec" "strings"
securejoin "github.com/cyphar/filepath-securejoin" "github.com/urfave/cli/v3" "tangled.sh/tangled.sh/core/appview/idresolver" "tangled.sh/tangled.sh/core/log")
func Command() *cli.Command { return &cli.Command{ Name: "guard", Usage: "role-based access control for git over ssh (not for manual use)", Action: Run, Flags: []cli.Flag{ &cli.StringFlag{ Name: "user", Usage: "allowed git user", Required: true, }, &cli.StringFlag{ Name: "git-dir", Usage: "base directory for git repos", Value: "/home/git", }, &cli.StringFlag{ Name: "log-path", Usage: "path to log file", Value: "/home/git/guard.log", }, &cli.StringFlag{ Name: "internal-api", Usage: "internal API endpoint", Value: "http://localhost:5444", }, }, }}
func Run(ctx context.Context, cmd *cli.Command) error { l := log.FromContext(ctx)
incomingUser := cmd.String("user") gitDir := cmd.String("git-dir") logPath := cmd.String("log-path") endpoint := cmd.String("internal-api")
logFile, err := os.OpenFile(logPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644) if err != nil { l.Error("failed to open log file", "error", err) return err } else { fileHandler := slog.NewJSONHandler(logFile, &slog.HandlerOptions{Level: slog.LevelInfo}) l = slog.New(fileHandler) }
var clientIP string if connInfo := os.Getenv("SSH_CONNECTION"); connInfo != "" { parts := strings.Fields(connInfo) if len(parts) > 0 { clientIP = parts[0] } }
if incomingUser == "" { l.Error("access denied: no user specified") fmt.Fprintln(os.Stderr, "access denied: no user specified") return fmt.Errorf("access denied: no user specified") }
sshCommand := os.Getenv("SSH_ORIGINAL_COMMAND")
l.Info("connection attempt", "user", incomingUser, "command", sshCommand, "client", clientIP)
if sshCommand == "" { l.Error("access denied: no interactive shells", "user", incomingUser) fmt.Fprintln(os.Stderr, "access denied: we don't serve interactive shells :)") os.Exit(-1) }
cmdParts := strings.Fields(sshCommand) if len(cmdParts) < 2 { l.Error("invalid command format", "command", sshCommand) fmt.Fprintln(os.Stderr, "invalid command format") return fmt.Errorf("invalid command format") }
gitCommand := cmdParts[0]
// did:foo/repo-name or // handle/repo-name or // any of the above with a leading slash (/)
components := strings.Split(strings.TrimPrefix(strings.Trim(cmdParts[1], "'"), "/"), "/") l.Info("command components", "components", components)
if len(components) != 2 { l.Error("invalid repo format", "components", components) fmt.Fprintln(os.Stderr, "invalid repo format, needs <user>/<repo> or /<user>/<repo>") return fmt.Errorf("invalid repo format, needs <user>/<repo> or /<user>/<repo>") }
didOrHandle := components[0] did := resolveToDid(ctx, l, didOrHandle) repoName := components[1] qualifiedRepoName, _ := securejoin.SecureJoin(did, repoName)
validCommands := map[string]bool{ "git-receive-pack": true, "git-upload-pack": true, "git-upload-archive": true, } if !validCommands[gitCommand] { l.Error("access denied: invalid git command", "command", gitCommand) fmt.Fprintln(os.Stderr, "access denied: invalid git command") return fmt.Errorf("access denied: invalid git command") }
if gitCommand != "git-upload-pack" { if !isPushPermitted(l, incomingUser, qualifiedRepoName, endpoint) { l.Error("access denied: user not allowed", "did", incomingUser, "reponame", qualifiedRepoName) fmt.Fprintln(os.Stderr, "access denied: user not allowed") return fmt.Errorf("access denied: user not allowed") } }
fullPath, _ := securejoin.SecureJoin(gitDir, qualifiedRepoName)
l.Info("processing command", "user", incomingUser, "command", gitCommand, "repo", repoName, "fullPath", fullPath, "client", clientIP)
if gitCommand == "git-upload-pack" { fmt.Fprintf(os.Stderr, "\x02%s\n", "Welcome to this knot!") } else { fmt.Fprintf(os.Stderr, "%s\n", "Welcome to this knot!") }
gitCmd := exec.Command(gitCommand, fullPath) gitCmd.Stdout = os.Stdout gitCmd.Stderr = os.Stderr gitCmd.Stdin = os.Stdin
if err := gitCmd.Run(); err != nil { l.Error("command failed", "error", err) fmt.Fprintf(os.Stderr, "command failed: %v\n", err) return fmt.Errorf("command failed: %v", err) }
l.Info("command completed", "user", incomingUser, "command", gitCommand, "repo", repoName, "success", true)
return nil}
func resolveToDid(ctx context.Context, l *slog.Logger, didOrHandle string) string { resolver := idresolver.DefaultResolver() ident, err := resolver.ResolveIdent(ctx, didOrHandle) if err != nil { l.Error("Error resolving handle", "error", err, "handle", didOrHandle) fmt.Fprintf(os.Stderr, "error resolving handle: %v\n", err) os.Exit(1) }
// did:plc:foobarbaz/repo return ident.DID.String()}
func isPushPermitted(l *slog.Logger, user, qualifiedRepoName, endpoint string) bool { u, _ := url.Parse(endpoint + "/push-allowed") q := u.Query() q.Add("user", user) q.Add("repo", qualifiedRepoName) u.RawQuery = q.Encode()
req, err := http.Get(u.String()) if err != nil { l.Error("Error verifying permissions", "error", err) fmt.Fprintf(os.Stderr, "error verifying permissions: %v\n", err) os.Exit(1) }
l.Info("Checking push permission", "url", u.String(), "status", req.Status)
return req.StatusCode == http.StatusNoContent}