Process links in layers to ignore the target

When a lyaer contains the creation of the symbolic link, the target
of the link is added to the layer as well. If the file being linked
to is in the RPM db, it will cause a failure since the RPM version
doesn't change, but the file is included. So, to work around this,
we will track the link targets, then remove them from the list of
layer files.

Signed-off-by: Brad P. Crochet <brad@redhat.com>

internal/policy/container/has_modified_files.go

@@ -382,7 +382,9 @@ func generateChangesFor(layer v1.Layer) ([]string, error) {
 	}
 	defer layerReader.Close()
 	tarReader := tar.NewReader(layerReader)
-	var filelist []string
+	// Use a map so we can remove items easily. Will turn this into a string slice before returning
+	filelist := make(map[string]struct{})
+	var links []string
 	for {
 		header, err := tarReader.Next()
 		if errors.Is(err, io.EOF) {
@@ -408,16 +410,31 @@ func generateChangesFor(layer v1.Layer) ([]string, error) {
 		}
 		switch {
 		case (header.Typeflag == tar.TypeDir && tombstone) || header.Typeflag == tar.TypeReg:
-			filelist = append(filelist, strings.TrimPrefix(filepath.Join(dirname, basename), "/"))
-		case header.Typeflag == tar.TypeSymlink:
-			filelist = append(filelist, strings.TrimPrefix(header.Name, "/"))
+			filelist[strings.TrimPrefix(filepath.Join(dirname, basename), "/")] = struct{}{}
+		case header.Typeflag == tar.TypeSymlink || header.Typeflag == tar.TypeLink:
+			filelist[strings.TrimPrefix(header.Name, "/")] = struct{}{}
+			// Add the target to the links slice so we can remove them later
+			links = append(links, strings.TrimPrefix(header.Linkname, "/"))
 		default:
 			// TODO: what do we do with other flags?
 			continue
 		}
 	}
 
-	return filelist, nil
+	// We have to process these after the fact, as the link could have come before
+	// the target in the tarball
+	// As it stands now, this really only works for links that the target is a fully
+	// qualified path. If the link was relative, this probably doesn't work.
+	for _, link := range links {
+		delete(filelist, link)
+	}
+
+	keys := make([]string, 0, len(filelist))
+	for k := range filelist {
+		keys = append(keys, k)
+	}
+
+	return keys, nil
 }
 
 // ExtractRPMDB copies /var/lib/rpm/* from the archive and derives a list of packages from