Auto-disable apps that cancel the entire backup

This can happen when the app process gets killed while its BackupAgent is running. There are several qcom apps in the wild that have this issue. These are DoSing our backups and are non-free, so we are defending ourselves against them.

app/src/main/java/com/stevesoltys/seedvault/App.kt

@@ -2,6 +2,7 @@ package com.stevesoltys.seedvault
 
 import android.Manifest.permission.INTERACT_ACROSS_USERS_FULL
 import android.app.Application
+import android.app.backup.BackupManager
 import android.app.backup.BackupManager.PACKAGE_MANAGER_SENTINEL
 import android.app.backup.IBackupManager
 import android.content.Context
@@ -147,9 +148,10 @@ open class App : Application() {
 
 }
 
-const val MAGIC_PACKAGE_MANAGER = PACKAGE_MANAGER_SENTINEL
+const val MAGIC_PACKAGE_MANAGER: String = PACKAGE_MANAGER_SENTINEL
 const val ANCESTRAL_RECORD_KEY = "@ancestral_record@"
 const val GLOBAL_METADATA_KEY = "@meta@"
+const val ERROR_BACKUP_CANCELLED: Int = BackupManager.ERROR_BACKUP_CANCELLED
 
 // TODO this doesn't work for LineageOS as they do public debug builds
 fun isDebugBuild() = Build.TYPE == "userdebug"

app/src/main/java/com/stevesoltys/seedvault/settings/SettingsManager.kt

@@ -166,6 +166,15 @@ class SettingsManager(private val context: Context) {
 
     fun isBackupEnabled(packageName: String) = !blacklistedApps.contains(packageName)
 
+    /**
+     * Disables backup for an app. Similar to [onAppBackupStatusChanged].
+     */
+    fun disableBackup(packageName: String) {
+        if (blacklistedApps.add(packageName)) {
+            prefs.edit().putStringSet(PREF_KEY_BACKUP_APP_BLACKLIST, blacklistedApps).apply()
+        }
+    }
+
     fun isStorageBackupEnabled() = prefs.getBoolean(PREF_KEY_BACKUP_STORAGE, false)
 
     @UiThread

app/src/main/java/com/stevesoltys/seedvault/ui/notification/NotificationBackupObserver.kt

@@ -1,6 +1,7 @@
 package com.stevesoltys.seedvault.ui.notification
 
 import android.app.backup.BackupProgress
+import android.app.backup.BackupTransport.AGENT_ERROR
 import android.app.backup.IBackupObserver
 import android.content.Context
 import android.content.pm.ApplicationInfo.FLAG_SYSTEM
@@ -8,9 +9,11 @@ import android.content.pm.PackageManager.NameNotFoundException
 import android.util.Log
 import android.util.Log.INFO
 import android.util.Log.isLoggable
+import com.stevesoltys.seedvault.ERROR_BACKUP_CANCELLED
 import com.stevesoltys.seedvault.MAGIC_PACKAGE_MANAGER
 import com.stevesoltys.seedvault.R
 import com.stevesoltys.seedvault.metadata.MetadataManager
+import com.stevesoltys.seedvault.settings.SettingsManager
 import com.stevesoltys.seedvault.transport.backup.PackageService
 import com.stevesoltys.seedvault.worker.BackupRequester
 import org.koin.core.component.KoinComponent
@@ -27,11 +30,14 @@ internal class NotificationBackupObserver(
     private val nm: BackupNotificationManager by inject()
     private val metadataManager: MetadataManager by inject()
     private val packageService: PackageService by inject()
+    private val settingsManager: SettingsManager by inject()
     private var currentPackage: String? = null
     private var numPackages: Int = 0
     private var numPackagesToReport: Int = 0
     private var pmCounted: Boolean = false
 
+    private var errorPackageName: String? = null
+
     init {
         // Inform the notification manager that a backup has started
         // and inform about the expected numbers of apps.
@@ -86,6 +92,17 @@ internal class NotificationBackupObserver(
             // should only happen for MAGIC_PACKAGE_MANAGER, but better save than sorry
             Log.e(TAG, "Error getting ApplicationInfo: ", e)
         }
+
+        // Apps that get killed while interacting with their [BackupAgent] cancel the entire backup.
+        // In order to prevent them from DoSing us, we remember them here to auto-disable them.
+        // We noticed that the same app behavior can cause a status of
+        // either AGENT_ERROR or ERROR_BACKUP_CANCELLED, so we need to handle both.
+        errorPackageName = if (status == AGENT_ERROR || status == ERROR_BACKUP_CANCELLED) {
+            target
+        } else {
+            null // To not disable apps by mistake, we reset it when getting a new non-error result.
+        }
+
         // often [onResult] gets called right away without any [onUpdate] call
         showProgressNotification(target)
     }
@@ -98,6 +115,15 @@ internal class NotificationBackupObserver(
      *   as a whole failed.
      */
     override fun backupFinished(status: Int) {
+        if (status == ERROR_BACKUP_CANCELLED) {
+            val packageName = errorPackageName
+            if (packageName == null) {
+                Log.e(TAG, "Backup got cancelled, but there we have no culprit :(")
+            } else {
+                Log.w(TAG, "App $packageName misbehaved, will disable backup for it...")
+                settingsManager.disableBackup(packageName)
+            }
+        }
         if (backupRequester.requestNext()) {
             if (isLoggable(TAG, INFO)) {
                 Log.i(TAG, "Backup finished $numPackages/$requestedPackages. Status: $status")