| 1 | //go:build linux |
| 2 | |
| 3 | // Command reasonix-update-helper (Linux) installs a verified .deb under Polkit. |
| 4 | // It is invoked only via pkexec with fixed argv and re-validates every input as |
| 5 | // root before calling apt-get. The unprivileged desktop process never runs apt. |
| 6 | package main |
| 7 | |
| 8 | import ( |
| 9 | "bytes" |
| 10 | "encoding/json" |
| 11 | "errors" |
| 12 | "flag" |
| 13 | "fmt" |
| 14 | "io" |
| 15 | "os" |
| 16 | "os/exec" |
| 17 | "path/filepath" |
| 18 | "regexp" |
| 19 | "runtime" |
| 20 | "strconv" |
| 21 | "strings" |
| 22 | "syscall" |
| 23 | |
| 24 | "reasonix/desktop/internal/update" |
| 25 | ) |
| 26 | |
| 27 | // Stable exit codes observed by the desktop installer. |
| 28 | const ( |
| 29 | exitOK = 0 |
| 30 | exitUsage = 2 |
| 31 | exitNotRoot = 10 |
| 32 | exitBadInput = 11 |
| 33 | exitVerifyFailed = 12 |
| 34 | exitPackageRejected = 13 |
| 35 | exitBusy = 14 |
| 36 | exitInstallFailed = 15 |
| 37 | exitPostVerify = 16 |
| 38 | ) |
| 39 | |
| 40 | const ( |
| 41 | packageName = "reasonix-desktop" |
| 42 | dpkgDebPath = "/usr/bin/dpkg-deb" |
| 43 | dpkgQueryPath = "/usr/bin/dpkg-query" |
| 44 | dpkgPath = "/usr/bin/dpkg" |
| 45 | aptGetPath = "/usr/bin/apt-get" |
| 46 | |
| 47 | // maxInputBytes bounds untrusted package/signature files before they are |
| 48 | // copied into the root temp directory (desktop .deb + minisig). |
| 49 | maxInputBytes = 512 << 20 // 512 MiB |
| 50 | |
| 51 | // phasePrefix is a single-line protocol the desktop parses from stderr so |
| 52 | // the UI can leave "authorizing" once Polkit has launched this helper and |
| 53 | // validation finished, before apt-get starts. |
| 54 | phasePrefix = "REASONIX_UPDATE_PHASE=" |
| 55 | ) |
| 56 | |
| 57 | type helperResult struct { |
| 58 | OK bool `json:"ok"` |
| 59 | Version string `json:"version,omitempty"` |
| 60 | Error string `json:"error,omitempty"` |
| 61 | Code string `json:"code,omitempty"` |
| 62 | } |
| 63 | |
| 64 | // installDeps holds the privileged install seams. Production uses realDeps(); |
| 65 | // tests inject fakes so every branch is deterministic without root/apt. |
| 66 | type installDeps struct { |
| 67 | geteuid func() int |
| 68 | getenv func(string) string |
| 69 | mkTempDir func() (string, error) |
| 70 | removeAll func(string) error |
| 71 | copyOwnedRegular func(src, dst string, mode os.FileMode, ownerUID int, maxBytes int64) error |
| 72 | readFile func(string) ([]byte, error) |
| 73 | verify func(data, sig []byte) error |
| 74 | inspectDeb func(path string) (debIdentity, error) |
| 75 | installedVersion func() (string, error) |
| 76 | compareVersions func(a, b string) (int, error) |
| 77 | aptInstall func(pkgPath string, allowDowngrade bool) error |
| 78 | verifyInstalled func(want string) error |
| 79 | writePhase func(phase string) |
| 80 | writeResult func(helperResult) |
| 81 | goArch string |
| 82 | maxInputBytes int64 |
| 83 | } |
| 84 | |
| 85 | func realDeps() installDeps { |
| 86 | return installDeps{ |
| 87 | geteuid: os.Geteuid, |
| 88 | getenv: os.Getenv, |
| 89 | mkTempDir: func() (string, error) { return os.MkdirTemp("", "reasonix-update-*") }, |
| 90 | removeAll: os.RemoveAll, |
| 91 | copyOwnedRegular: copyOwnedRegularFile, |
| 92 | readFile: os.ReadFile, |
| 93 | verify: update.Verify, |
| 94 | inspectDeb: inspectDeb, |
| 95 | installedVersion: installedPackageVersion, |
| 96 | compareVersions: compareDebVersions, |
| 97 | aptInstall: aptInstallOnlyUpgrade, |
| 98 | verifyInstalled: verifyInstalled, |
| 99 | writePhase: writePhaseLine, |
| 100 | writeResult: writeResultJSON, |
| 101 | goArch: runtime.GOARCH, |
| 102 | maxInputBytes: maxInputBytes, |
| 103 | } |
| 104 | } |
| 105 | |
| 106 | func main() { |
| 107 | os.Exit(run(os.Args[1:])) |
| 108 | } |
| 109 | |
| 110 | func run(args []string) int { |
| 111 | return runWith(realDeps(), args) |
| 112 | } |
| 113 | |
| 114 | func runWith(d installDeps, args []string) int { |
| 115 | if len(args) == 0 { |
| 116 | d.writeResult(helperResult{OK: false, Error: "missing command", Code: "usage"}) |
| 117 | return exitUsage |
| 118 | } |
| 119 | switch args[0] { |
| 120 | case "install": |
| 121 | return runInstall(d, args[1:]) |
| 122 | default: |
| 123 | d.writeResult(helperResult{OK: false, Error: "unknown command", Code: "usage"}) |
| 124 | return exitUsage |
| 125 | } |
| 126 | } |
| 127 | |
| 128 | func runInstall(d installDeps, args []string) int { |
| 129 | fs := flag.NewFlagSet("install", flag.ContinueOnError) |
| 130 | fs.SetOutput(io.Discard) |
| 131 | var packagePath, signaturePath string |
| 132 | fs.StringVar(&packagePath, "package", "", "path to the verified .deb") |
| 133 | fs.StringVar(&signaturePath, "signature", "", "path to the detached .minisig") |
| 134 | if err := fs.Parse(args); err != nil { |
| 135 | d.writeResult(helperResult{OK: false, Error: "invalid arguments", Code: "usage"}) |
| 136 | return exitUsage |
| 137 | } |
| 138 | if packagePath == "" || signaturePath == "" || fs.NArg() != 0 { |
| 139 | d.writeResult(helperResult{OK: false, Error: "install requires --package and --signature", Code: "usage"}) |
| 140 | return exitUsage |
| 141 | } |
| 142 | |
| 143 | if d.geteuid() != 0 { |
| 144 | d.writeResult(helperResult{OK: false, Error: "helper must run as root", Code: "not_root"}) |
| 145 | return exitNotRoot |
| 146 | } |
| 147 | pkUID, err := strconv.Atoi(strings.TrimSpace(d.getenv("PKEXEC_UID"))) |
| 148 | if err != nil || pkUID < 0 { |
| 149 | d.writeResult(helperResult{OK: false, Error: "missing or invalid PKEXEC_UID", Code: "not_root"}) |
| 150 | return exitNotRoot |
| 151 | } |
| 152 | |
| 153 | tmpDir, err := d.mkTempDir() |
| 154 | if err != nil { |
| 155 | d.writeResult(helperResult{OK: false, Error: "create temp dir failed", Code: "install_failed"}) |
| 156 | return exitInstallFailed |
| 157 | } |
| 158 | // Ensure root-only access before any untrusted bytes land here. |
| 159 | if err := os.Chmod(tmpDir, 0o700); err != nil { |
| 160 | _ = d.removeAll(tmpDir) |
| 161 | d.writeResult(helperResult{OK: false, Error: "secure temp dir failed", Code: "install_failed"}) |
| 162 | return exitInstallFailed |
| 163 | } |
| 164 | defer func() { _ = d.removeAll(tmpDir) }() |
| 165 | |
| 166 | maxBytes := d.maxInputBytes |
| 167 | if maxBytes <= 0 { |
| 168 | maxBytes = maxInputBytes |
| 169 | } |
| 170 | pkgCopy := filepath.Join(tmpDir, "package.deb") |
| 171 | sigCopy := filepath.Join(tmpDir, "package.deb.minisig") |
| 172 | if err := d.copyOwnedRegular(packagePath, pkgCopy, 0o600, pkUID, maxBytes); err != nil { |
| 173 | d.writeResult(helperResult{OK: false, Error: "invalid package input", Code: "bad_input"}) |
| 174 | return exitBadInput |
| 175 | } |
| 176 | if err := d.copyOwnedRegular(signaturePath, sigCopy, 0o600, pkUID, maxBytes); err != nil { |
| 177 | d.writeResult(helperResult{OK: false, Error: "invalid signature input", Code: "bad_input"}) |
| 178 | return exitBadInput |
| 179 | } |
| 180 | |
| 181 | pkgData, err := d.readFile(pkgCopy) |
| 182 | if err != nil { |
| 183 | d.writeResult(helperResult{OK: false, Error: "read package failed", Code: "bad_input"}) |
| 184 | return exitBadInput |
| 185 | } |
| 186 | sigData, err := d.readFile(sigCopy) |
| 187 | if err != nil { |
| 188 | d.writeResult(helperResult{OK: false, Error: "read signature failed", Code: "bad_input"}) |
| 189 | return exitBadInput |
| 190 | } |
| 191 | // Re-verify as root; never trust the unprivileged process's prior check. |
| 192 | if err := d.verify(pkgData, sigData); err != nil { |
| 193 | d.writeResult(helperResult{OK: false, Error: "signature verification failed", Code: "verify_failed"}) |
| 194 | return exitVerifyFailed |
| 195 | } |
| 196 | |
| 197 | candidate, err := d.inspectDeb(pkgCopy) |
| 198 | if err != nil { |
| 199 | d.writeResult(helperResult{OK: false, Error: err.Error(), Code: "package_rejected"}) |
| 200 | return exitPackageRejected |
| 201 | } |
| 202 | if err := acceptDebIdentity(candidate, d.goArch); err != nil { |
| 203 | d.writeResult(helperResult{OK: false, Error: err.Error(), Code: "package_rejected"}) |
| 204 | return exitPackageRejected |
| 205 | } |
| 206 | |
| 207 | installed, err := d.installedVersion() |
| 208 | if err != nil { |
| 209 | d.writeResult(helperResult{OK: false, Error: err.Error(), Code: "package_rejected"}) |
| 210 | return exitPackageRejected |
| 211 | } |
| 212 | cmp, err := d.compareVersions(candidate.Version, installed) |
| 213 | if err != nil { |
| 214 | d.writeResult(helperResult{OK: false, Error: "version compare failed", Code: "package_rejected"}) |
| 215 | return exitPackageRejected |
| 216 | } |
| 217 | allowDowngrade, err := acceptVersionTransition(cmp, candidate.Version, installed) |
| 218 | if err != nil { |
| 219 | d.writeResult(helperResult{OK: false, Error: err.Error(), Code: "package_rejected"}) |
| 220 | return exitPackageRejected |
| 221 | } |
| 222 | |
| 223 | // Polkit already authorized this process; validation is complete. Tell the |
| 224 | // desktop to leave "authorizing" before the long apt-get call. |
| 225 | d.writePhase("installing") |
| 226 | |
| 227 | if err := d.aptInstall(pkgCopy, allowDowngrade); err != nil { |
| 228 | code := "install_failed" |
| 229 | exit := exitInstallFailed |
| 230 | if isPackageManagerBusy(err) { |
| 231 | code = "package_manager_busy" |
| 232 | exit = exitBusy |
| 233 | } |
| 234 | d.writeResult(helperResult{OK: false, Error: sanitizeHelperError(err), Code: code}) |
| 235 | return exit |
| 236 | } |
| 237 | |
| 238 | if err := d.verifyInstalled(candidate.Version); err != nil { |
| 239 | d.writeResult(helperResult{OK: false, Error: err.Error(), Code: "package_verify_failed"}) |
| 240 | return exitPostVerify |
| 241 | } |
| 242 | |
| 243 | d.writeResult(helperResult{OK: true, Version: candidate.Version}) |
| 244 | return exitOK |
| 245 | } |
| 246 | |
| 247 | type debIdentity struct { |
| 248 | Package string |
| 249 | Version string |
| 250 | Arch string |
| 251 | } |
| 252 | |
| 253 | // acceptDebIdentity enforces package name and architecture. Pure for tests. |
| 254 | func acceptDebIdentity(id debIdentity, goArch string) error { |
| 255 | if id.Package != packageName { |
| 256 | return errors.New("package name rejected") |
| 257 | } |
| 258 | wantArch := goArch |
| 259 | if wantArch == "386" { |
| 260 | wantArch = "i386" |
| 261 | } |
| 262 | if id.Arch != wantArch && id.Arch != "all" { |
| 263 | return errors.New("package architecture rejected") |
| 264 | } |
| 265 | if id.Version == "" { |
| 266 | return errors.New("package version missing") |
| 267 | } |
| 268 | return nil |
| 269 | } |
| 270 | |
| 271 | var ( |
| 272 | stableDebVersionRE = regexp.MustCompile(`^(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)$`) |
| 273 | previewDebVersionRE = regexp.MustCompile(`^(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)~preview\.(0|[1-9][0-9]*)$`) |
| 274 | ) |
| 275 | |
| 276 | // acceptVersionTransition permits ordinary upgrades and the one intentional |
| 277 | // downgrade: replacing a public Preview package with a public Stable package |
| 278 | // after the user switches channels. |
| 279 | func acceptVersionTransition(cmp int, candidate, installed string) (bool, error) { |
| 280 | switch { |
| 281 | case cmp > 0: |
| 282 | return false, nil |
| 283 | case cmp == 0: |
| 284 | return false, errors.New("candidate version is not strictly newer") |
| 285 | case stableDebVersionRE.MatchString(candidate) && previewDebVersionRE.MatchString(installed): |
| 286 | return true, nil |
| 287 | default: |
| 288 | return false, errors.New("candidate downgrade is not an allowed preview-to-stable transition") |
| 289 | } |
| 290 | } |
| 291 | |
| 292 | // aptInstallArgv is the fixed absolute apt-get argv (never shell). Pure for tests. |
| 293 | func aptInstallArgv(pkgPath string, allowDowngrade bool) []string { |
| 294 | argv := []string{ |
| 295 | aptGetPath, |
| 296 | "install", |
| 297 | "--assume-yes", |
| 298 | "--only-upgrade", |
| 299 | "--no-remove", |
| 300 | } |
| 301 | if allowDowngrade { |
| 302 | argv = append(argv, "--allow-downgrades") |
| 303 | } |
| 304 | return append(argv, pkgPath) |
| 305 | } |
| 306 | |
| 307 | func inspectDeb(path string) (debIdentity, error) { |
| 308 | pkg, err := dpkgDebField(path, "Package") |
| 309 | if err != nil { |
| 310 | return debIdentity{}, errors.New("dpkg-deb inspection failed") |
| 311 | } |
| 312 | ver, err := dpkgDebField(path, "Version") |
| 313 | if err != nil { |
| 314 | return debIdentity{}, errors.New("dpkg-deb inspection failed") |
| 315 | } |
| 316 | arch, err := dpkgDebField(path, "Architecture") |
| 317 | if err != nil { |
| 318 | return debIdentity{}, errors.New("dpkg-deb inspection failed") |
| 319 | } |
| 320 | return debIdentity{Package: pkg, Version: ver, Arch: arch}, nil |
| 321 | } |
| 322 | |
| 323 | func dpkgDebField(path, field string) (string, error) { |
| 324 | out, err := exec.Command(dpkgDebPath, "-f", path, field).Output() |
| 325 | if err != nil { |
| 326 | return "", err |
| 327 | } |
| 328 | return strings.TrimSpace(string(out)), nil |
| 329 | } |
| 330 | |
| 331 | func installedPackageVersion() (string, error) { |
| 332 | out, err := exec.Command(dpkgQueryPath, "-W", "-f=${Version}", packageName).Output() |
| 333 | if err != nil { |
| 334 | return "", errors.New("installed package not found") |
| 335 | } |
| 336 | v := strings.TrimSpace(string(out)) |
| 337 | if v == "" { |
| 338 | return "", errors.New("installed package version empty") |
| 339 | } |
| 340 | return v, nil |
| 341 | } |
| 342 | |
| 343 | // compareDebVersions returns >0 when a > b using dpkg --compare-versions. |
| 344 | func compareDebVersions(a, b string) (int, error) { |
| 345 | if err := exec.Command(dpkgPath, "--compare-versions", a, "gt", b).Run(); err == nil { |
| 346 | return 1, nil |
| 347 | } |
| 348 | if err := exec.Command(dpkgPath, "--compare-versions", a, "eq", b).Run(); err == nil { |
| 349 | return 0, nil |
| 350 | } |
| 351 | if err := exec.Command(dpkgPath, "--compare-versions", a, "lt", b).Run(); err == nil { |
| 352 | return -1, nil |
| 353 | } |
| 354 | return 0, errors.New("compare-versions failed") |
| 355 | } |
| 356 | |
| 357 | func aptInstallOnlyUpgrade(pkgPath string, allowDowngrade bool) error { |
| 358 | argv := aptInstallArgv(pkgPath, allowDowngrade) |
| 359 | cmd := exec.Command(argv[0], argv[1:]...) |
| 360 | // Fixed absolute argv only — never shell. |
| 361 | cmd.Env = append(os.Environ(), "DEBIAN_FRONTEND=noninteractive") |
| 362 | var stderr bytes.Buffer |
| 363 | cmd.Stdout = io.Discard |
| 364 | cmd.Stderr = &stderr |
| 365 | if err := cmd.Run(); err != nil { |
| 366 | return fmt.Errorf("%w: %s", err, strings.TrimSpace(stderr.String())) |
| 367 | } |
| 368 | return nil |
| 369 | } |
| 370 | |
| 371 | func verifyInstalled(wantVersion string) error { |
| 372 | out, err := exec.Command(dpkgQueryPath, "-W", "-f=${Status}\n${Version}", packageName).Output() |
| 373 | if err != nil { |
| 374 | return errors.New("post-install dpkg-query failed") |
| 375 | } |
| 376 | lines := strings.Split(strings.TrimSpace(string(out)), "\n") |
| 377 | if len(lines) < 2 { |
| 378 | return errors.New("post-install package state incomplete") |
| 379 | } |
| 380 | if strings.TrimSpace(lines[0]) != "install ok installed" { |
| 381 | return errors.New("package not in install ok installed state") |
| 382 | } |
| 383 | if strings.TrimSpace(lines[1]) != wantVersion { |
| 384 | return errors.New("installed version mismatch") |
| 385 | } |
| 386 | return nil |
| 387 | } |
| 388 | |
| 389 | // copyOwnedRegularFile opens src with O_NOFOLLOW only (fail closed — no Lstat/Open |
| 390 | // fallback), requires a regular file owned by ownerUID, enforces maxBytes, and |
| 391 | // writes a root-owned copy at dst. Ownership is checked on the opened fd. |
| 392 | func copyOwnedRegularFile(src, dst string, mode os.FileMode, ownerUID int, maxBytes int64) error { |
| 393 | f, err := os.OpenFile(src, os.O_RDONLY|syscall.O_NOFOLLOW, 0) |
| 394 | if err != nil { |
| 395 | // Fail closed: never fall back to a followable open (TOCTOU). |
| 396 | return fmt.Errorf("open without following links: %w", err) |
| 397 | } |
| 398 | defer f.Close() |
| 399 | |
| 400 | info, err := f.Stat() |
| 401 | if err != nil { |
| 402 | return err |
| 403 | } |
| 404 | if !info.Mode().IsRegular() { |
| 405 | return errors.New("not a regular file") |
| 406 | } |
| 407 | if maxBytes > 0 && info.Size() > maxBytes { |
| 408 | return errors.New("input exceeds size bound") |
| 409 | } |
| 410 | st, ok := info.Sys().(*syscall.Stat_t) |
| 411 | if !ok { |
| 412 | return errors.New("stat owner unavailable") |
| 413 | } |
| 414 | if int(st.Uid) != ownerUID { |
| 415 | return errors.New("input owner does not match PKEXEC_UID") |
| 416 | } |
| 417 | |
| 418 | out, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_EXCL, mode) |
| 419 | if err != nil { |
| 420 | return err |
| 421 | } |
| 422 | defer out.Close() |
| 423 | // Cap the copy even if size grew after Stat (regular files can still be |
| 424 | // truncated/appended by the owner on some filesystems; bound the bytes we take). |
| 425 | limited := io.LimitReader(f, maxBytes+1) |
| 426 | n, err := io.Copy(out, limited) |
| 427 | if err != nil { |
| 428 | return err |
| 429 | } |
| 430 | if maxBytes > 0 && n > maxBytes { |
| 431 | return errors.New("input exceeds size bound") |
| 432 | } |
| 433 | return out.Close() |
| 434 | } |
| 435 | |
| 436 | func isPackageManagerBusy(err error) bool { |
| 437 | if err == nil { |
| 438 | return false |
| 439 | } |
| 440 | low := strings.ToLower(err.Error()) |
| 441 | return strings.Contains(low, "could not get lock") || |
| 442 | strings.Contains(low, "unable to acquire the dpkg frontend lock") || |
| 443 | strings.Contains(low, "is another process using it") || |
| 444 | strings.Contains(low, "dpkg frontend lock") |
| 445 | } |
| 446 | |
| 447 | // sanitizeHelperError strips absolute paths from helper diagnostics so the |
| 448 | // desktop UI never surfaces user home directories. |
| 449 | func sanitizeHelperError(err error) string { |
| 450 | if err == nil { |
| 451 | return "install failed" |
| 452 | } |
| 453 | msg := err.Error() |
| 454 | // Drop anything that looks like an absolute path segment. |
| 455 | fields := strings.Fields(msg) |
| 456 | for i, f := range fields { |
| 457 | if strings.HasPrefix(f, "/") { |
| 458 | fields[i] = "<path>" |
| 459 | } |
| 460 | } |
| 461 | out := strings.Join(fields, " ") |
| 462 | if out == "" { |
| 463 | return "install failed" |
| 464 | } |
| 465 | if len(out) > 240 { |
| 466 | out = out[:240] |
| 467 | } |
| 468 | return out |
| 469 | } |
| 470 | |
| 471 | func writePhaseLine(phase string) { |
| 472 | // Single line, no user paths — desktop parses this while the helper runs. |
| 473 | fmt.Fprintf(os.Stderr, "%s%s\n", phasePrefix, phase) |
| 474 | } |
| 475 | |
| 476 | func writeResultJSON(r helperResult) { |
| 477 | enc := json.NewEncoder(os.Stdout) |
| 478 | _ = enc.Encode(r) |
| 479 | } |
| 480 | |
| 481 | // parsePhaseLine extracts a progress phase from a helper stderr line. |
| 482 | func parsePhaseLine(line string) (phase string, ok bool) { |
| 483 | line = strings.TrimSpace(line) |
| 484 | if !strings.HasPrefix(line, phasePrefix) { |
| 485 | return "", false |
| 486 | } |
| 487 | phase = strings.TrimSpace(strings.TrimPrefix(line, phasePrefix)) |
| 488 | return phase, phase != "" |
| 489 | } |
| 490 |