From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jing Ji <jji@google.com>
Date: Tue, 25 Oct 2022 22:39:52 -0700
Subject: [PATCH] DO NOT MERGE: ActivityManager#killBackgroundProcesses can
 kill caller's own app only

unless it's a system app.

Bug: 239423414
Bug: 223376078
Test: atest CtsAppTestCases:ActivityManagerTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:8b382775b258220466a977453905797521e159de)
Merged-In: Iac6baa889965b8ffecd9a43179a4c96632ad1d02
Change-Id: Iac6baa889965b8ffecd9a43179a4c96632ad1d02
---
 core/java/android/app/ActivityManager.java    |  3 ++
 core/res/AndroidManifest.xml                  |  6 +++-
 .../server/am/ActivityManagerService.java     | 32 +++++++++++++++++--
 3 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/core/java/android/app/ActivityManager.java b/core/java/android/app/ActivityManager.java
index da7d711194de..9f6e25c74386 100644
--- a/core/java/android/app/ActivityManager.java
+++ b/core/java/android/app/ActivityManager.java
@@ -3160,6 +3160,9 @@ public class ActivityManager {
      * processes to reclaim memory; the system will take care of restarting
      * these processes in the future as needed.
      *
+     * <p class="note">Third party applications can only use this API to kill their own processes.
+     * </p>
+     *
      * <p>You must hold the permission
      * {@link android.Manifest.permission#KILL_BACKGROUND_PROCESSES} to be able to
      * call this method.
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 0f224dae3337..ef6ce2503061 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -1741,7 +1741,11 @@
         android:protectionLevel="normal" />
 
     <!-- Allows an application to call
-        {@link android.app.ActivityManager#killBackgroundProcesses}.
+         {@link android.app.ActivityManager#killBackgroundProcesses}.
+
+         <p class="note">Third party applications can only use this API to kill their own
+         processes.</p>
+
          <p>Protection level: normal
     -->
     <permission android:name="android.permission.KILL_BACKGROUND_PROCESSES"
diff --git a/services/core/java/com/android/server/am/ActivityManagerService.java b/services/core/java/com/android/server/am/ActivityManagerService.java
index 8f26804d51bd..a96ad5e24399 100644
--- a/services/core/java/com/android/server/am/ActivityManagerService.java
+++ b/services/core/java/com/android/server/am/ActivityManagerService.java
@@ -5819,8 +5819,20 @@ public final class ActivityManagerService extends ActivityManagerNative
             Slog.w(TAG, msg);
             throw new SecurityException(msg);
         }
+        final int callingUid = Binder.getCallingUid();
+        final int callingPid = Binder.getCallingPid();
+        final int callingAppId = UserHandle.getAppId(callingUid);
 
-        userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(),
+        ProcessRecord proc;
+        synchronized (mPidsSelfLocked) {
+            proc = mPidsSelfLocked.get(callingPid);
+        }
+        final boolean hasKillAllPermission = PERMISSION_GRANTED == checkPermission(
+                android.Manifest.permission.FORCE_STOP_PACKAGES, callingPid, callingUid)
+                || (UserHandle.getAppId(callingUid) > 0 && UserHandle.getAppId(callingUid) < Process.FIRST_APPLICATION_UID)
+                || (proc != null && proc.info.isSystemApp());
+
+        userId = mUserController.handleIncomingUser(callingPid, callingUid,
                 userId, true, ALLOW_FULL_ONLY, "killBackgroundProcesses", null);
         long callingId = Binder.clearCallingIdentity();
         try {
@@ -5832,7 +5844,7 @@ public final class ActivityManagerService extends ActivityManagerNative
                             pm.getPackageUid(packageName, MATCH_DEBUG_TRIAGED_MISSING, userId));
                 } catch (RemoteException e) {
                 }
-                if (appId == -1) {
+                if (appId == -1 || (!hasKillAllPermission && appId != callingAppId)) {
                     Slog.w(TAG, "Invalid packageName: " + packageName);
                     return;
                 }
@@ -5912,6 +5924,22 @@ public final class ActivityManagerService extends ActivityManagerNative
             throw new SecurityException(msg);
         }
 
+        final int callingUid = Binder.getCallingUid();
+        final int callingPid = Binder.getCallingPid();
+
+        ProcessRecord proc;
+        synchronized (mPidsSelfLocked) {
+            proc = mPidsSelfLocked.get(callingPid);
+        }
+        if (callingUid >= Process.FIRST_APPLICATION_UID
+                && (proc == null || !proc.info.isSystemApp())) {
+            final String msg = "Permission Denial: killAllBackgroundProcesses() from pid="
+                    + callingPid + ", uid=" + callingUid + " is not allowed";
+            Slog.w(TAG, msg);
+            // Silently return to avoid existing apps from crashing.
+            return;
+        }
+
         final long callingId = Binder.clearCallingIdentity();
         try {
             synchronized (this) {
