prevent again security warning about 'Zip Slip' in RPI camera downloader (#6108)

internal/staticsources/rpicamera/mtxrpicamdownloader/main.go

@@ -21,13 +21,18 @@ const (
 	maxInboundRPICameraSize = 10 * 1024 * 1024
 )
 
-func safeArchivePath(name string) (string, error) {
+func safeArchivePath(baseDir string, name string) (string, error) {
 	name = filepath.Clean(filepath.FromSlash(name))
-	if filepath.IsAbs(name) || name == ".." || strings.HasPrefix(name, ".."+string(filepath.Separator)) {
+	if name == "." || !filepath.IsLocal(name) {
 		return "", fmt.Errorf("invalid archive entry: %s", name)
 	}
 
-	return name, nil
+	targetPath := filepath.Join(baseDir, name)
+	if targetPath != baseDir && !strings.HasPrefix(targetPath, baseDir+string(filepath.Separator)) {
+		return "", fmt.Errorf("invalid archive entry: %s", name)
+	}
+
+	return targetPath, nil
 }
 
 func dumpTar(src io.Reader) error {
@@ -36,7 +41,11 @@ func dumpTar(src io.Reader) error {
 		return err
 	}
 
-	baseDir := "."
+	baseDir, err := filepath.Abs(".")
+	if err != nil {
+		return err
+	}
+
 	tr := tar.NewReader(uncompressed)
 
 	for {
@@ -49,14 +58,12 @@ func dumpTar(src io.Reader) error {
 			return err
 		}
 
-		var entryName string
-		entryName, err = safeArchivePath(header.Name)
+		var targetPath string
+		targetPath, err = safeArchivePath(baseDir, header.Name)
 		if err != nil {
 			return err
 		}
 
-		targetPath := filepath.Join(baseDir, entryName)
-
 		switch header.Typeflag {
 		case tar.TypeDir:
 			err = os.Mkdir(targetPath, header.FileInfo().Mode())

internal/staticsources/rpicamera/mtxrpicamdownloader/main_test.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestSafeArchivePath(t *testing.T) {
+	baseDir := filepath.Clean(string(filepath.Separator) + filepath.Join("tmp", "base"))
+
+	for _, ca := range []struct {
+		name   string
+		path   string
+		ok     bool
+		result string
+	}{
+		{
+			name:   "simple file",
+			path:   "dir/file",
+			ok:     true,
+			result: filepath.Join(baseDir, "dir", "file"),
+		},
+		{
+			name: "parent traversal",
+			path: "../file",
+		},
+		{
+			name: "absolute path",
+			path: "/etc/passwd",
+		},
+		{
+			name: "empty path",
+			path: "",
+		},
+		{
+			name: "dot path",
+			path: ".",
+		},
+	} {
+		t.Run(ca.name, func(t *testing.T) {
+			res, err := safeArchivePath(baseDir, ca.path)
+			if ca.ok {
+				if err != nil {
+					t.Fatalf("unexpected error: %v", err)
+				}
+				if res != ca.result {
+					t.Fatalf("unexpected result: got %q, want %q", res, ca.result)
+				}
+			} else if err == nil {
+				t.Fatalf("expected error")
+			}
+		})
+	}
+}