From 037f0a4c91aacd9d2d7f8191d6dc532034f8441a Mon Sep 17 00:00:00 2001
From: Alexander Neumann <alexander@bumpern.de>
Date: Sat, 21 Nov 2020 21:45:54 +0100
Subject: [PATCH] Refactor device ID checking

---
 cmd/restic/exclude.go | 81 ++++++++++++++++++++++++++++---------------
 1 file changed, 53 insertions(+), 28 deletions(-)

diff --git a/cmd/restic/exclude.go b/cmd/restic/exclude.go
index 540a3d2ff..3c6000877 100644
--- a/cmd/restic/exclude.go
+++ b/cmd/restic/exclude.go
@@ -199,12 +199,17 @@ func isDirExcludedByFile(dir, tagFilename, header string) bool {
 	return true
 }
 
-// gatherDevices returns the set of unique device ids of the files and/or
-// directory paths listed in "items".
-func gatherDevices(items []string) (deviceMap map[string]uint64, err error) {
-	deviceMap = make(map[string]uint64)
-	for _, item := range items {
-		item, err = filepath.Abs(filepath.Clean(item))
+// DeviceMap is used to track allowed source devices for backup. This is used to
+// check for crossing mount points during backup (for --one-file-system). It
+// maps the name of a source path to its device ID.
+type DeviceMap map[string]uint64
+
+// NewDeviceMap creates a new device map from the list of source paths.
+func NewDeviceMap(allowedSourcePaths []string) (DeviceMap, error) {
+	deviceMap := make(map[string]uint64)
+
+	for _, item := range allowedSourcePaths {
+		item, err := filepath.Abs(filepath.Clean(item))
 		if err != nil {
 			return nil, err
 		}
@@ -213,30 +218,63 @@ func gatherDevices(items []string) (deviceMap map[string]uint64, err error) {
 		if err != nil {
 			return nil, err
 		}
+
 		id, err := fs.DeviceID(fi)
 		if err != nil {
 			return nil, err
 		}
+
 		deviceMap[item] = id
 	}
+
 	if len(deviceMap) == 0 {
 		return nil, errors.New("zero allowed devices")
 	}
+
 	return deviceMap, nil
 }
 
+// IsAllowed returns true if the path is located on an allowed device.
+func (m DeviceMap) IsAllowed(item string, deviceID uint64) (bool, error) {
+	for dir := item; ; dir = filepath.Dir(dir) {
+		debug.Log("item %v, test dir %v", item, dir)
+
+		// find a parent directory that is on an allowed device (otherwise
+		// we would not traverse the directory at all)
+		allowedID, ok := m[dir]
+		if !ok {
+			if dir == filepath.Dir(dir) {
+				// arrived at root, no allowed device found. this should not happen.
+				break
+			}
+			continue
+		}
+
+		// if the item has a different device ID than the parent directory,
+		// we crossed a file system boundary
+		if allowedID != deviceID {
+			debug.Log("item %v (dir %v) on disallowed device %d", item, dir, deviceID)
+			return false, nil
+		}
+
+		// item is on allowed device, accept it
+		debug.Log("item %v allowed", item)
+		return true, nil
+	}
+
+	return false, fmt.Errorf("item %v (device ID %v) not found, deviceMap: %v", item, deviceID, m)
+}
+
 // rejectByDevice returns a RejectFunc that rejects files which are on a
 // different file systems than the files/dirs in samples.
 func rejectByDevice(samples []string) (RejectFunc, error) {
-	allowed, err := gatherDevices(samples)
+	deviceMap, err := NewDeviceMap(samples)
 	if err != nil {
 		return nil, err
 	}
-	debug.Log("allowed devices: %v\n", allowed)
+	debug.Log("allowed devices: %v\n", deviceMap)
 
 	return func(item string, fi os.FileInfo) bool {
-		item = filepath.Clean(item)
-
 		id, err := fs.DeviceID(fi)
 		if err != nil {
 			// This should never happen because gatherDevices() would have
@@ -244,26 +282,13 @@ func rejectByDevice(samples []string) (RejectFunc, error) {
 			panic(err)
 		}
 
-		for dir := item; ; dir = filepath.Dir(dir) {
-			debug.Log("item %v, test dir %v", item, dir)
-
-			allowedID, ok := allowed[dir]
-			if !ok {
-				if dir == filepath.Dir(dir) {
-					break
-				}
-				continue
-			}
-
-			if allowedID != id {
-				debug.Log("path %q on disallowed device %d", item, id)
-				return true
-			}
-
-			return false
+		allowed, err := deviceMap.IsAllowed(filepath.Clean(item), id)
+		if err != nil {
+			// this should not happen
+			panic(fmt.Sprintf("error checking device ID of %v: %v", item, err))
 		}
 
-		panic(fmt.Sprintf("item %v, device id %v not found, allowedDevs: %v", item, id, allowed))
+		return !allowed
 	}, nil
 }