BinaryTransparencyService: Fix getOriginalApexPreinstalledLocation

The existing `getOriginalApexPreinstalledLocation` method makes use
of heuristics to determine the filename of originally APEXs
preinstalled on the /system/apex directory.

This change fixes the method to perform prefix comparison instead
of relying on previous heuristics, and thus making this method
more robust overall against package name mismatch, and provides
clear error signals now.

Bug: 259349011
Test: atest BinaryTransparencyServiceTest
Change-Id: Iff6d1041c71e10522f744b9569f5827bb14ed238

1 files changed, 16 insertions, 8 deletions

diff --git a/services/core/java/com/android/server/BinaryTransparencyService.java b/services/core/java/com/android/server/BinaryTransparencyService.java
index 544dd4e6dcff..68880bd09a40 100644
--- a/services/core/java/com/android/server/BinaryTransparencyService.java
+++ b/services/core/java/com/android/server/BinaryTransparencyService.java
@@ -73,6 +73,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.Executors;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * @hide
@@ -104,6 +105,9 @@ public class BinaryTransparencyService extends SystemService {
     @VisibleForTesting
     static final String BUNDLE_CONTENT_DIGEST = "content-digest";
 
+    static final String APEX_PRELOAD_LOCATION = "/system/apex/";
+    static final String APEX_PRELOAD_LOCATION_ERROR = "could-not-be-determined";
+
     // used for indicating any type of error during MBA measurement
     static final int MBA_STATUS_ERROR = 0;
     // used for indicating factory condition preloads
@@ -1110,18 +1114,22 @@ public class BinaryTransparencyService extends SystemService {
         }
     }
 
-    // TODO(b/259349011): Need to be more robust against package name mismatch in the filename
+    @NonNull
     private String getOriginalApexPreinstalledLocation(String packageName,
                                                    String currentInstalledLocation) {
-        if (currentInstalledLocation.contains("/decompressed/")) {
-            String resultPath = "system/apex" + packageName + ".capex";
-            File f = new File(resultPath);
-            if (f.exists()) {
-                return resultPath;
+        // get a listing of all apex files in /system/apex/
+        Set<String> originalApexs = Stream.of(new File(APEX_PRELOAD_LOCATION).listFiles())
+                                        .filter(f -> !f.isDirectory())
+                                        .map(File::getName)
+                                        .collect(Collectors.toSet());
+
+        for (String originalApex : originalApexs) {
+            if (originalApex.startsWith(packageName)) {
+                return APEX_PRELOAD_LOCATION + originalApex;
             }
-            return "/system/apex/" + packageName + ".next.capex";
         }
-        return "/system/apex" + packageName + "apex";
+
+        return APEX_PRELOAD_LOCATION_ERROR;
     }
 
     /**