{"record":{"id":"2fa252f174668cd6","repo":"JuliusBrussee/caveman","slug":"native-session-key-chmod-w","errorCode":null,"errorMessage":"native session key chmod: %w","messagePattern":"native session key chmod: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"proxy/internal/nativeruntime/marker.go","lineNumber":64,"sourceCode":"\t\t\treturn nil, fmt.Errorf(\"native session key sync: %w\", syncErr)\n\t\t}\n\t\tif closeErr := file.Close(); closeErr != nil {\n\t\t\treturn nil, fmt.Errorf(\"native session key close: %w\", closeErr)\n\t\t}\n\t\treturn key, nil\n\t}\n\tif !errors.Is(err, os.ErrExist) {\n\t\treturn nil, fmt.Errorf(\"native session key create: %w\", err)\n\t}\n\tkey, err = os.ReadFile(path)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"native session key read: %w\", err)\n\t}\n\tif len(key) != sessionKeyBytes {\n\t\treturn nil, fmt.Errorf(\"native session key length = %d, want %d\", len(key), sessionKeyBytes)\n\t}\n\tif err := os.Chmod(path, 0o600); err != nil {\n\t\treturn nil, fmt.Errorf(\"native session key chmod: %w\", err)\n\t}\n\treturn key, nil\n}\n\n// SessionMarker builds model-temporary correlation context. Local proxy removes\n// valid markers byte-surgically before provider inspection or forwarding.\nfunc SessionMarker(key []byte, sessionID string) (string, error) {\n\tif len(key) != sessionKeyBytes || sessionID == \"\" || len(sessionID) > 256 {\n\t\treturn \"\", errors.New(\"native session marker: invalid key or session id\")\n\t}\n\tencoded := base64.RawURLEncoding.EncodeToString([]byte(sessionID))\n\tsig := markerMAC(key, encoded)\n\treturn fmt.Sprintf(`[[caveman-session-v1 sid=\"%s\" sig=\"%s\"]]`, encoded, sig), nil\n}\n\n// StripSessionMarkers removes only valid HMAC-signed markers. Invalid marker-\n// shaped user text remains byte-identical. Conflicting valid session IDs are\n// stripped but return no correlation identity.","sourceCodeStart":46,"sourceCodeEnd":82,"githubUrl":"https://github.com/JuliusBrussee/caveman/blob/766dce6b1394ebb56a3090748d5a0240a5aefb36/proxy/internal/nativeruntime/marker.go#L46-L82","documentation":"The existing session.key passed the 32-byte size check but os.Chmod(path, 0600) failed. Almost always the file is owned by a different uid (a previous sudo run minted it), and chmod on a file you do not own is denied even inside a directory you control. The runtime enforces 0600 as a hard invariant for the shared HMAC key, so it refuses to continue with a group/world-readable key.","triggerScenarios":"session.key created under sudo/root and then caveman run as the normal user; the file was copied in by another user with ownership preserved; the immutable attribute was set on the file.","commonSituations":"The sudo-first-run pattern on shared machines; homes restored by an admin; files migrated between accounts with cp -p.","solutions":["sudo chown $(id -u):$(id -g) <home>/runtime/session.key","Or discard and re-mint: sudo rm <home>/runtime/session.key, then restart as the normal user","Stop launching caveman under sudo; fix the launcher script","lsattr <home>/runtime/session.key to rule out the immutable attribute"],"exampleFix":null,"handlingStrategy":"validation","validationCode":"keyPath := filepath.Join(home, \"runtime\", \"session.key\")\nif info, err := os.Stat(keyPath); err == nil {\n\tif st, ok := info.Sys().(*syscall.Stat_t); ok && int(st.Uid) != os.Getuid() {\n\t\treturn fmt.Errorf(\"%s owned by uid %d — run: sudo chown %d:%d %s (or remove it to re-mint)\", keyPath, st.Uid, os.Getuid(), os.Getgid(), keyPath)\n\t}\n}\n// safe to call nativeruntime.LoadOrCreateSessionKey(home)","typeGuard":"func isPermissionErr(err error) bool {\n\treturn errors.Is(err, fs.ErrPermission)\n}","tryCatchPattern":"key, err := nativeruntime.LoadOrCreateSessionKey(home)\nif err != nil {\n\tif errors.Is(err, fs.ErrPermission) && strings.Contains(err.Error(), \"session key chmod\") {\n\t\tlog.Printf(\"key file is foreign-owned — sudo chown %d:%d %s or sudo rm it and restart\", os.Getuid(), os.Getgid(), filepath.Join(home, \"runtime\", \"session.key\"))\n\t}\n\treturn err\n}","preventionTips":["Never run caveman under sudo — the minted key ends up root-owned and every later unprivileged start fails the 0600 enforce","When migrating accounts, chown the runtime dir and key together with the home","After any admin restores files into the home, verify key ownership before starting","Removing the foreign key is always safe recovery: a new one is minted, only old marker correlation is lost"],"tags":["go","filesystem","permissions","sudo"],"backgroundTag":"chmod-permission-denied","analyzedSha":"766dce6b1394ebb56a3090748d5a0240a5aefb36","analyzedAt":"2026-08-18T03:14:35.516Z","contentChangedAt":"2026-08-18T03:14:35.516Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}