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| 1 | +// SPDX-License-Identifier: AGPL-3.0-or-later |
| 2 | + |
| 3 | +package main |
| 4 | + |
| 5 | +import ( |
| 6 | + "context" |
| 7 | + "fmt" |
| 8 | + "net/netip" |
| 9 | + "os" |
| 10 | + "strings" |
| 11 | + "time" |
| 12 | + |
| 13 | + "github.com/spf13/cobra" |
| 14 | + |
| 15 | + "github.com/tenseleyFlow/shithub/internal/infra/config" |
| 16 | + "github.com/tenseleyFlow/shithub/internal/infra/db" |
| 17 | + usersdb "github.com/tenseleyFlow/shithub/internal/users/sqlc" |
| 18 | +) |
| 19 | + |
| 20 | +// sshAuthkeysCmd implements sshd's AuthorizedKeysCommand contract: |
| 21 | +// |
| 22 | +// - On a known fingerprint, write a single authorized_keys line on stdout |
| 23 | +// with a forced command and restrictive options. |
| 24 | +// - On an unknown fingerprint OR any error, write nothing and exit 0. |
| 25 | +// sshd uses STDOUT as the auth answer; non-zero exit is a config error, |
| 26 | +// not a deny. Failing closed is the right model: better to deny a |
| 27 | +// legitimate connection than accidentally authorize the wrong user. |
| 28 | +// |
| 29 | +// Latency is critical — every SSH connection waits on this. The pool is |
| 30 | +// sized small (max 4 conns) to bound startup cost and tail-latency. |
| 31 | +var sshAuthkeysCmd = &cobra.Command{ |
| 32 | + Use: "ssh-authkeys <fingerprint>", |
| 33 | + Short: "AuthorizedKeysCommand handler for sshd", |
| 34 | + Args: cobra.ExactArgs(1), |
| 35 | + Hidden: true, // not for direct human use |
| 36 | + RunE: func(cmd *cobra.Command, args []string) error { |
| 37 | + // Fail-closed wrapper: anything below that returns an error or |
| 38 | + // panics writes nothing to stdout. The exit code stays 0. |
| 39 | + defer func() { |
| 40 | + _ = recover() |
| 41 | + }() |
| 42 | + fp := strings.TrimSpace(args[0]) |
| 43 | + if !isWellFormedFingerprint(fp) { |
| 44 | + return nil |
| 45 | + } |
| 46 | + |
| 47 | + cfg, err := config.Load(nil) |
| 48 | + if err != nil || cfg.DB.URL == "" { |
| 49 | + return nil |
| 50 | + } |
| 51 | + |
| 52 | + ctx, cancel := context.WithTimeout(cmd.Context(), 1500*time.Millisecond) |
| 53 | + defer cancel() |
| 54 | + |
| 55 | + pool, err := db.Open(ctx, db.Config{ |
| 56 | + URL: cfg.DB.URL, MaxConns: 4, MinConns: 0, |
| 57 | + ConnectTimeout: 750 * time.Millisecond, |
| 58 | + }) |
| 59 | + if err != nil { |
| 60 | + return nil |
| 61 | + } |
| 62 | + defer pool.Close() |
| 63 | + |
| 64 | + q := usersdb.New() |
| 65 | + row, err := q.GetUserSSHKeyByFingerprint(ctx, pool, fp) |
| 66 | + if err != nil { |
| 67 | + // pgx.ErrNoRows or any other error → silently empty. |
| 68 | + return nil |
| 69 | + } |
| 70 | + |
| 71 | + _, _ = fmt.Fprintln(cmd.OutOrStdout(), authorizedKeysLine(row)) |
| 72 | + |
| 73 | + // Best-effort last-used update. 500ms cap; any error is dropped. |
| 74 | + updateCtx, updateCancel := context.WithTimeout(context.Background(), 500*time.Millisecond) |
| 75 | + defer updateCancel() |
| 76 | + _ = q.TouchSSHKeyLastUsed(updateCtx, pool, usersdb.TouchSSHKeyLastUsedParams{ |
| 77 | + ID: row.ID, |
| 78 | + LastUsedIp: clientAddrFromEnv(), |
| 79 | + }) |
| 80 | + return nil |
| 81 | + }, |
| 82 | +} |
| 83 | + |
| 84 | +// sshShellCmd is the placeholder for the forced-command target. S13 swaps |
| 85 | +// this for the real git-over-SSH dispatcher; for S07 we just log the |
| 86 | +// inbound command and exit non-zero with a friendly message so an |
| 87 | +// operator (or test) can confirm the wiring works end-to-end. |
| 88 | +var sshShellCmd = &cobra.Command{ |
| 89 | + Use: "ssh-shell <user_id>", |
| 90 | + Short: "Forced-command target invoked by sshd via AuthorizedKeysCommand", |
| 91 | + Args: cobra.ExactArgs(1), |
| 92 | + Hidden: true, |
| 93 | + RunE: func(cmd *cobra.Command, args []string) error { |
| 94 | + userID := args[0] |
| 95 | + original := os.Getenv("SSH_ORIGINAL_COMMAND") |
| 96 | + // Log to stderr so it's captured by sshd's session log without |
| 97 | + // polluting the (silent-on-empty) stdout contract. |
| 98 | + _, _ = fmt.Fprintf(cmd.ErrOrStderr(), |
| 99 | + "shithubd ssh-shell: user_id=%s original_command=%q (git-over-SSH lands in S13)\n", |
| 100 | + userID, original) |
| 101 | + return fmt.Errorf("git over SSH not enabled yet") |
| 102 | + }, |
| 103 | +} |
| 104 | + |
| 105 | +// authorizedKeysLine builds the single line sshd consumes. The forced |
| 106 | +// command runs `shithubd ssh-shell <user_id>`; the option set strips |
| 107 | +// every interactive affordance. |
| 108 | +func authorizedKeysLine(row usersdb.UserSshKey) string { |
| 109 | + binary := os.Args[0] |
| 110 | + // Quote-escape only the binary path; user_id is a digit string so it |
| 111 | + // can never contain shell metacharacters. |
| 112 | + cmd := fmt.Sprintf(`%s ssh-shell %d`, binary, row.UserID) |
| 113 | + options := strings.Join([]string{ |
| 114 | + fmt.Sprintf(`command="%s"`, cmd), |
| 115 | + "no-port-forwarding", |
| 116 | + "no-X11-forwarding", |
| 117 | + "no-agent-forwarding", |
| 118 | + "no-pty", |
| 119 | + }, ",") |
| 120 | + return options + " " + row.PublicKey |
| 121 | +} |
| 122 | + |
| 123 | +// clientAddrFromEnv extracts the connecting client's address from |
| 124 | +// $SSH_CONNECTION (sshd sets it to "<client> <cport> <server> <sport>"). |
| 125 | +// Returns nil when unavailable, which sqlc encodes as a SQL NULL. |
| 126 | +func clientAddrFromEnv() *netip.Addr { |
| 127 | + conn := os.Getenv("SSH_CONNECTION") |
| 128 | + if conn == "" { |
| 129 | + return nil |
| 130 | + } |
| 131 | + parts := strings.Fields(conn) |
| 132 | + if len(parts) < 1 { |
| 133 | + return nil |
| 134 | + } |
| 135 | + addr, err := netip.ParseAddr(parts[0]) |
| 136 | + if err != nil { |
| 137 | + return nil |
| 138 | + } |
| 139 | + return &addr |
| 140 | +} |
| 141 | + |
| 142 | +// isWellFormedFingerprint accepts only the canonical SHA256:<b64> shape |
| 143 | +// our codebase emits. Defense against an attacker passing crafted strings |
| 144 | +// to influence the SQL plan. |
| 145 | +func isWellFormedFingerprint(s string) bool { |
| 146 | + if !strings.HasPrefix(s, "SHA256:") { |
| 147 | + return false |
| 148 | + } |
| 149 | + rest := s[len("SHA256:"):] |
| 150 | + if len(rest) < 30 || len(rest) > 80 { |
| 151 | + return false |
| 152 | + } |
| 153 | + for _, r := range rest { |
| 154 | + switch { |
| 155 | + case r >= 'A' && r <= 'Z', |
| 156 | + r >= 'a' && r <= 'z', |
| 157 | + r >= '0' && r <= '9', |
| 158 | + r == '+', r == '/', r == '=': |
| 159 | + default: |
| 160 | + return false |
| 161 | + } |
| 162 | + } |
| 163 | + return true |
| 164 | +} |
| 165 | + |
| 166 | +func init() { |
| 167 | + rootCmd.AddCommand(sshAuthkeysCmd) |
| 168 | + rootCmd.AddCommand(sshShellCmd) |
| 169 | +} |