Caddy vulnerable to cross-origin config application via local admin API /load (caddy)

@@ -1029,6 +1029,13 @@ func handleConfig(w http.ResponseWriter, r *http.Request) error {
 			return err
 		}
 
+		// If this request changed the config, clear the last
+		// config info we have stored, if it is different from
+		// the original source.
+		ClearLastConfigIfDifferent(
+			r.Header.Get("Caddy-Config-Source-File"),
+			r.Header.Get("Caddy-Config-Source-Adapter"))
+
 	default:
 		return APIError{
 			HTTPStatus: http.StatusMethodNotAllowed,

@@ -121,6 +121,13 @@ func (adminLoad) handleLoad(w http.ResponseWriter, r *http.Request) error {
 		}
 	}
 
+	// If this request changed the config, clear the last
+	// config info we have stored, if it is different from
+	// the original source.
+	caddy.ClearLastConfigIfDifferent(
+		r.Header.Get("Caddy-Config-Source-File"),
+		r.Header.Get("Caddy-Config-Source-Adapter"))
+
 	caddy.Log().Named("admin.api").Info("load complete")
 
 	return nil

@@ -1197,6 +1197,91 @@ var (
 	rawCfgMu sync.RWMutex
 )
 
+// lastConfigFile and lastConfigAdapter remember the source config
+// file and adapter used when Caddy was started via the CLI "run" command.
+// These are consulted by the SIGUSR1 handler to attempt reloading from
+// the same source. They are intentionally not set for other entrypoints
+// such as "caddy start" or subcommands like file-server.
+var (
+	lastConfigMu      sync.RWMutex
+	lastConfigFile    string
+	lastConfigAdapter string
+)
+
+// reloadFromSourceFunc is the type of stored callback
+// which is called when we receive a SIGUSR1 signal.
+type reloadFromSourceFunc func(file, adapter string) error
+
+// reloadFromSourceCallback is the stored callback
+// which is called when we receive a SIGUSR1 signal.
+var reloadFromSourceCallback reloadFromSourceFunc
+
+// errReloadFromSourceUnavailable is returned when no reload-from-source callback is set.
+var errReloadFromSourceUnavailable = errors.New("reload from source unavailable in this process") //nolint:unused
+
+// SetLastConfig records the given source file and adapter as the
+// last-known external configuration source. Intended to be called
+// only when starting via "caddy run --config <file> --adapter <adapter>".
+func SetLastConfig(file, adapter string, fn reloadFromSourceFunc) {
+	lastConfigMu.Lock()
+	lastConfigFile = file
+	lastConfigAdapter = adapter
+	reloadFromSourceCallback = fn
+	lastConfigMu.Unlock()
+}
+
+// ClearLastConfigIfDifferent clears the recorded last-config if the provided
+// source file/adapter do not match the recorded last-config. If both srcFile
+// and srcAdapter are empty, the last-config is cleared.
+func ClearLastConfigIfDifferent(srcFile, srcAdapter string) {
+	if (srcFile != "" || srcAdapter != "") && lastConfigMatches(srcFile, srcAdapter) {
+		return
+	}
+	SetLastConfig("", "", nil)
+}
+
+// getLastConfig returns the last-known config file and adapter.
+func getLastConfig() (file, adapter string, fn reloadFromSourceFunc) {
+	lastConfigMu.RLock()
+	f, a, cb := lastConfigFile, lastConfigAdapter, reloadFromSourceCallback
+	lastConfigMu.RUnlock()
+	return f, a, cb
+}
+
+// lastConfigMatches returns true if the provided source file and/or adapter
+// matches the recorded last-config. Matching rules (in priority order):
+//  1. If srcAdapter is provided and differs from the recorded adapter, no match.
+//  2. If srcFile exactly equals the recorded file, match.
+//  3. If both sides can be made absolute and equal, match.
+//  4. If basenames are equal, match.
+func lastConfigMatches(srcFile, srcAdapter string) bool {
+	lf, la, _ := getLastConfig()
+
+	// If adapter is provided, it must match.
+	if srcAdapter != "" && srcAdapter != la {
+		return false
+	}
+
+	// Quick equality check.
+	if srcFile == lf {
+		return true
+	}
+
+	// Try absolute path comparison.
+	sAbs, sErr := filepath.Abs(srcFile)
+	lAbs, lErr := filepath.Abs(lf)
+	if sErr == nil && lErr == nil && sAbs == lAbs {
+		return true
+	}
+
+	// Final fallback: basename equality.
+	if filepath.Base(srcFile) == filepath.Base(lf) {
+		return true
+	}
+
+	return false
+}
+
 // errSameConfig is returned if the new config is the same
 // as the old one. This isn't usually an actual, actionable
 // error; it's mostly a sentinel value.

@@ -231,8 +231,9 @@ func cmdRun(fl Flags) (int, error) {
 	}
 	// we don't use 'else' here since this value might have been changed in 'if' block; i.e. not mutually exclusive
 	var configFile string
+	var adapterUsed string
 	if !resumeFlag {
-		config, configFile, err = LoadConfig(configFlag, configAdapterFlag)
+		config, configFile, adapterUsed, err = LoadConfig(configFlag, configAdapterFlag)
 		if err != nil {
 			logBuffer.FlushTo(defaultLogger)
 			return caddy.ExitCodeFailedStartup, err
@@ -249,6 +250,19 @@ func cmdRun(fl Flags) (int, error) {
 		}
 	}
 
+	// If we have a source config file (we're running via 'caddy run --config ...'),
+	// record it so SIGUSR1 can reload from the same file. Also provide a callback
+	// that knows how to load/adapt that source when requested by the main process.
+	if configFile != "" {
+		caddy.SetLastConfig(configFile, adapterUsed, func(file, adapter string) error {
+			cfg, _, _, err := LoadConfig(file, adapter)
+			if err != nil {
+				return err
+			}
+			return caddy.Load(cfg, true)
+		})
+	}
+
 	// run the initial config
 	err = caddy.Load(config, true)
 	if err != nil {
@@ -295,7 +309,7 @@ func cmdRun(fl Flags) (int, error) {
 	// if enabled, reload config file automatically on changes
 	// (this better only be used in dev!)
 	if watchFlag {
-		go watchConfigFile(configFile, configAdapterFlag)
+		go watchConfigFile(configFile, adapterUsed)
 	}
 
 	// warn if the environment does not provide enough information about the disk
@@ -350,7 +364,7 @@ func cmdReload(fl Flags) (int, error) {
 	forceFlag := fl.Bool("force")
 
 	// get the config in caddy's native format
-	config, configFile, err := LoadConfig(configFlag, configAdapterFlag)
+	config, configFile, adapterUsed, err := LoadConfig(configFlag, configAdapterFlag)
 	if err != nil {
 		return caddy.ExitCodeFailedStartup, err
 	}
@@ -368,6 +382,10 @@ func cmdReload(fl Flags) (int, error) {
 	if forceFlag {
 		headers.Set("Cache-Control", "must-revalidate")
 	}
+	// Provide the source file/adapter to the running process so it can
+	// preserve its last-config knowledge if this reload came from the same source.
+	headers.Set("Caddy-Config-Source-File", configFile)
+	headers.Set("Caddy-Config-Source-Adapter", adapterUsed)
 
 	resp, err := AdminAPIRequest(adminAddr, http.MethodPost, "/load", headers, bytes.NewReader(config))
 	if err != nil {
@@ -582,7 +600,7 @@ func cmdValidateConfig(fl Flags) (int, error) {
 			fmt.Errorf("input file required when there is no Caddyfile in current directory (use --config flag)")
 	}
 
-	input, _, err := LoadConfig(configFlag, adapterFlag)
+	input, _, _, err := LoadConfig(configFlag, adapterFlag)
 	if err != nil {
 		return caddy.ExitCodeFailedStartup, err
 	}
@@ -797,7 +815,7 @@ func DetermineAdminAPIAddress(address string, config []byte, configFile, configA
 		loadedConfig := config
 		if len(loadedConfig) == 0 {
 			// get the config in caddy's native format
-			loadedConfig, loadedConfigFile, err = LoadConfig(configFile, configAdapter)
+			loadedConfig, loadedConfigFile, _, err = LoadConfig(configFile, configAdapter)
 			if err != nil {
 				return "", err
 			}

@@ -100,7 +100,12 @@ func handlePingbackConn(conn net.Conn, expect []byte) error {
 // there is no config available. It prints any warnings to stderr,
 // and returns the resulting JSON config bytes along with
 // the name of the loaded config file (if any).
-func LoadConfig(configFile, adapterName string) ([]byte, string, error) {
+// The return values are:
+//   - config bytes (nil if no config)
+//   - config file used ("" if none)
+//   - adapter used ("" if none)
+//   - error, if any
+func LoadConfig(configFile, adapterName string) ([]byte, string, string, error) {
 	return loadConfigWithLogger(caddy.Log(), configFile, adapterName)
 }
 
@@ -138,7 +143,7 @@ func isCaddyfile(configFile, adapterName string) (bool, error) {
 	return false, nil
 }
 
-func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([]byte, string, error) {
+func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([]byte, string, string, error) {
 	// if no logger is provided, use a nop logger
 	// just so we don't have to check for nil
 	if logger == nil {
@@ -147,7 +152,7 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 
 	// specifying an adapter without a config file is ambiguous
 	if adapterName != "" && configFile == "" {
-		return nil, "", fmt.Errorf("cannot adapt config without config file (use --config)")
+		return nil, "", "", fmt.Errorf("cannot adapt config without config file (use --config)")
 	}
 
 	// load initial config and adapter
@@ -158,13 +163,13 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 		if configFile == "-" {
 			config, err = io.ReadAll(os.Stdin)
 			if err != nil {
-				return nil, "", fmt.Errorf("reading config from stdin: %v", err)
+				return nil, "", "", fmt.Errorf("reading config from stdin: %v", err)
 			}
 			logger.Info("using config from stdin")
 		} else {
 			config, err = os.ReadFile(configFile)
 			if err != nil {
-				return nil, "", fmt.Errorf("reading config from file: %v", err)
+				return nil, "", "", fmt.Errorf("reading config from file: %v", err)
 			}
 			logger.Info("using config from file", zap.String("file", configFile))
 		}
@@ -179,7 +184,7 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 				cfgAdapter = nil
 			} else if err != nil {
 				// default Caddyfile exists, but error reading it
-				return nil, "", fmt.Errorf("reading default Caddyfile: %v", err)
+				return nil, "", "", fmt.Errorf("reading default Caddyfile: %v", err)
 			} else {
 				// success reading default Caddyfile
 				configFile = "Caddyfile"
@@ -191,14 +196,14 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 	if yes, err := isCaddyfile(configFile, adapterName); yes {
 		adapterName = "caddyfile"
 	} else if err != nil {
-		return nil, "", err
+		return nil, "", "", err
 	}
 
 	// load config adapter
 	if adapterName != "" {
 		cfgAdapter = caddyconfig.GetAdapter(adapterName)
 		if cfgAdapter == nil {
-			return nil, "", fmt.Errorf("unrecognized config adapter: %s", adapterName)
+			return nil, "", "", fmt.Errorf("unrecognized config adapter: %s", adapterName)
 		}
 	}
 
@@ -208,7 +213,7 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 			"filename": configFile,
 		})
 		if err != nil {
-			return nil, "", fmt.Errorf("adapting config using %s: %v", adapterName, err)
+			return nil, "", "", fmt.Errorf("adapting config using %s: %v", adapterName, err)
 		}
 		logger.Info("adapted config to JSON", zap.String("adapter", adapterName))
 		for _, warn := range warnings {
@@ -226,11 +231,11 @@ func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([
 		// validate that the config is at least valid JSON
 		err = json.Unmarshal(config, new(any))
 		if err != nil {
-			return nil, "", fmt.Errorf("config is not valid JSON: %v; did you mean to use a config adapter (the --adapter flag)?", err)
+			return nil, "", "", fmt.Errorf("config is not valid JSON: %v; did you mean to use a config adapter (the --adapter flag)?", err)
 		}
 	}
 
-	return config, configFile, nil
+	return config, configFile, adapterName, nil
 }
 
 // watchConfigFile watches the config file at filename for changes
@@ -256,7 +261,7 @@ func watchConfigFile(filename, adapterName string) {
 	}
 
 	// get current config
-	lastCfg, _, err := loadConfigWithLogger(nil, filename, adapterName)
+	lastCfg, _, _, err := loadConfigWithLogger(nil, filename, adapterName)
 	if err != nil {
 		logger().Error("unable to load latest config", zap.Error(err))
 		return
@@ -268,7 +273,7 @@ func watchConfigFile(filename, adapterName string) {
 	//nolint:staticcheck
 	for range time.Tick(1 * time.Second) {
 		// get current config
-		newCfg, _, err := loadConfigWithLogger(nil, filename, adapterName)
+		newCfg, _, _, err := loadConfigWithLogger(nil, filename, adapterName)
 		if err != nil {
 			logger().Error("unable to load latest config", zap.Error(err))
 			return

@@ -36,7 +36,7 @@ type storVal struct {
 // determineStorage returns the top-level storage module from the given config.
 // It may return nil even if no error.
 func determineStorage(configFile string, configAdapter string) (*storVal, error) {
-	cfg, _, err := LoadConfig(configFile, configAdapter)
+	cfg, _, _, err := LoadConfig(configFile, configAdapter)
 	if err != nil {
 		return nil, err
 	}

@@ -18,6 +18,7 @@ package caddy
 
 import (
 	"context"
+	"errors"
 	"os"
 	"os/signal"
 	"syscall"
@@ -48,7 +49,31 @@ func trapSignalsPosix() {
 				exitProcessFromSignal("SIGTERM")
 
 			case syscall.SIGUSR1:
-				Log().Info("not implemented", zap.String("signal", "SIGUSR1"))
+				logger := Log().With(zap.String("signal", "SIGUSR1"))
+				// If we know the last source config file/adapter (set when starting
+				// via `caddy run --config <file> --adapter <adapter>`), attempt
+				// to reload from that source. Otherwise, ignore the signal.
+				file, adapter, reloadCallback := getLastConfig()
+				if file == "" {
+					logger.Info("last config unknown, ignored SIGUSR1")
+					break
+				}
+				logger = logger.With(
+					zap.String("file", file),
+					zap.String("adapter", adapter))
+				if reloadCallback == nil {
+					logger.Warn("no reload helper available, ignored SIGUSR1")
+					break
+				}
+				logger.Info("reloading config from last-known source")
+				if err := reloadCallback(file, adapter); errors.Is(err, errReloadFromSourceUnavailable) {
+					// No reload helper available (likely not started via caddy run).
+					logger.Warn("reload from source unavailable in this process; ignored SIGUSR1")
+				} else if err != nil {
+					logger.Error("failed to reload config from file", zap.Error(err))
+				} else {
+					logger.Info("successfully reloaded config from file")
+				}
 
 			case syscall.SIGUSR2:
 				Log().Info("not implemented", zap.String("signal", "SIGUSR2"))