Adding support for custom signature for grid customization

Bug: 403628674
Flag: EXEMPT flagging not supported
Test: Verified manually
Change-Id: I009cc3814c593b2906acd05cb19391cacc5fbaaa

AndroidManifest-common.xml

@@ -61,9 +61,14 @@
         android:protectionLevel="signatureOrSystem"
         android:label="@string/permlab_write_settings"
         android:description="@string/permdesc_write_settings"/>
+    <permission
+        android:name="${applicationId}.permission.GRID_CONTROL"
+        android:knownCerts="@array/grid_control_known_signers"
+        android:protectionLevel="signature|knownSigner"/>
 
     <uses-permission android:name="${applicationId}.permission.READ_SETTINGS" />
     <uses-permission android:name="${applicationId}.permission.WRITE_SETTINGS" />
+    <uses-permission android:name="${applicationId}.permission.GRID_CONTROL" />
 
     <application
         android:backupAgent="com.android.launcher3.LauncherBackupAgent"
@@ -131,11 +136,15 @@
             android:writePermission="${applicationId}.permission.WRITE_SETTINGS"
             android:readPermission="${applicationId}.permission.READ_SETTINGS" />
 
-        <!-- The content provider for exposing various launcher grid options. -->
+        <!--
+          The content provider for exposing various launcher grid options.
+          The caller should hold one of the following permissions:
+             - android.permission.BIND_WALLPAPER
+             - ${applicationId}.permission.GRID_CONTROL
+         -->
         <provider
             android:name="com.android.launcher3.graphics.LauncherCustomizationProvider"
             android:authorities="${applicationId}.grid_control"
-            android:permission="android.permission.BIND_WALLPAPER"
             android:exported="true" />
 
         <!--

res/values/config.xml

@@ -221,4 +221,6 @@
 
     <!-- Used to differentiate between desktop and non-desktop devices. -->
     <bool name="desktop_form_factor">false</bool>
+
+    <string-array name="grid_control_known_signers" translatable="false" />
 </resources>

src/com/android/launcher3/graphics/LauncherCustomizationProvider.kt

@@ -15,15 +15,55 @@
  */
 package com.android.launcher3.graphics
 
+import android.Manifest.permission.BIND_WALLPAPER
 import android.content.Context
+import android.content.pm.PackageManager
 import android.net.Uri
+import android.os.Binder
+import com.android.launcher3.BuildConfig.APPLICATION_ID
+import com.android.launcher3.R
 import com.android.launcher3.dagger.LauncherComponentProvider.appComponent
 import com.android.launcher3.util.ContentProviderProxy
+import java.security.MessageDigest
 
 /** Provider for various Launcher customizations exposed via a ContentProvider API */
 class LauncherCustomizationProvider : ContentProviderProxy() {
 
-    override fun getProxy(ctx: Context): ProxyProvider? = ctx.appComponent.gridCustomizationsProxy
+    override fun getProxy(ctx: Context): ProxyProvider? {
+        // Check if the caller has access
+        enforceCallerPermission(ctx)
+        return ctx.appComponent.gridCustomizationsProxy
+    }
+
+    private fun enforceCallerPermission(ctx: Context) {
+        if (ctx.checkCallingPermission(BIND_WALLPAPER) == PackageManager.PERMISSION_GRANTED) return
+        if (ctx.checkCallingPermission(PERM_GRID_CONTROL) == PackageManager.PERMISSION_GRANTED)
+            return
+
+        // Temporary change until the clients migrate to the new permission
+        val source = callingAttributionSource?.packageName ?: throw genericAccessException()
+        val signatures =
+            ctx.packageManager.getPackageInfo(source, PackageManager.GET_SIGNATURES)?.signatures
+                ?: throw genericAccessException()
+        val signature =
+            MessageDigest.getInstance("SHA-256")
+                .apply { signatures.forEach { update(it.toByteArray()) } }
+                .digest()
+                .joinToString("") { String.format("%02x", it) }
+        if (ctx.resources.getStringArray(R.array.grid_control_known_signers).contains(signature))
+            return
+        throw genericAccessException()
+    }
+
+    private fun genericAccessException() =
+        SecurityException(
+            "Permission Denial: opening provider com.android.launcher3.graphics.LauncherCustomizationProvider (pid=${Binder.getCallingPid()}, uid=${Binder.getCallingUid()}) requires $BIND_WALLPAPER or $PERM_GRID_CONTROL"
+        )
 
     override fun getType(uri: Uri) = "vnd.android.cursor.dir/launcher_grid"
+
+    companion object {
+
+        private const val PERM_GRID_CONTROL = "$APPLICATION_ID.permission.GRID_CONTROL"
+    }
 }