From 92f128c51c7a063595abe1e142617e43a0231797 Mon Sep 17 00:00:00 2001
From: paulhu <paulhu@google.com>
Date: Thu, 1 Jul 2021 18:04:45 +0800
Subject: [PATCH] Force only system uid can set uids allowed on restricted
 networks

- Check whether calling UID/PID is system_server.
- For CTS test, enforce NETWORK_SETTINGS permission otherwise if
  it's a debug build.

Bug: 175199465
Test: atest FrameworksNetTests
Test: atest ConnectivityManagerTest#testUidsAllowedOnRestrictedNetworks
Merged-In: I175a831671d3e52460d28203b09f6c0dda56b61c

Change-Id: I175a831671d3e52460d28203b09f6c0dda56b61c
---
 .../net/ConnectivitySettingsManager.java      | 20 +++++++++++++++++++
 .../net/cts/ConnectivityManagerTest.java      | 19 ++++++++++++------
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/framework/src/android/net/ConnectivitySettingsManager.java b/framework/src/android/net/ConnectivitySettingsManager.java
index 085de6b685..8fc0065347 100644
--- a/framework/src/android/net/ConnectivitySettingsManager.java
+++ b/framework/src/android/net/ConnectivitySettingsManager.java
@@ -29,6 +29,8 @@ import android.annotation.Nullable;
 import android.annotation.SystemApi;
 import android.content.Context;
 import android.net.ConnectivityManager.MultipathPreference;
+import android.os.Binder;
+import android.os.Build;
 import android.os.Process;
 import android.os.UserHandle;
 import android.provider.Settings;
@@ -1039,6 +1041,15 @@ public class ConnectivitySettingsManager {
         return getUidSetFromString(uidList);
     }
 
+    private static boolean isCallingFromSystem() {
+        final int uid = Binder.getCallingUid();
+        final int pid = Binder.getCallingPid();
+        if (uid == Process.SYSTEM_UID && pid == Process.myPid()) {
+            return true;
+        }
+        return false;
+    }
+
     /**
      * Set the list of uids(from {@link Settings}) that is allowed to use restricted networks.
      *
@@ -1047,6 +1058,15 @@ public class ConnectivitySettingsManager {
      */
     public static void setUidsAllowedOnRestrictedNetworks(@NonNull Context context,
             @NonNull Set<Integer> uidList) {
+        final boolean calledFromSystem = isCallingFromSystem();
+        if (!calledFromSystem) {
+            // Enforce NETWORK_SETTINGS check if it's debug build. This is for MTS test only.
+            if (!Build.isDebuggable()) {
+                throw new SecurityException("Only system can set this setting.");
+            }
+            context.enforceCallingOrSelfPermission(android.Manifest.permission.NETWORK_SETTINGS,
+                    "Requires NETWORK_SETTINGS permission");
+        }
         final String uids = getUidStringFromSet(uidList);
         Settings.Global.putString(context.getContentResolver(), UIDS_ALLOWED_ON_RESTRICTED_NETWORKS,
                 uids);
diff --git a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
index cd5281ff2b..527897eba2 100644
--- a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
+++ b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
@@ -2876,6 +2876,10 @@ public class ConnectivityManagerTest {
     public void testUidsAllowedOnRestrictedNetworks() throws Exception {
         assumeTrue(TestUtils.shouldTestSApis());
 
+        // TODO (b/175199465): figure out a reasonable permission check for
+        //  setUidsAllowedOnRestrictedNetworks that allows tests but not system-external callers.
+        assumeTrue(Build.isDebuggable());
+
         final int uid = mPackageManager.getPackageUid(mContext.getPackageName(), 0 /* flag */);
         final Set<Integer> originalUidsAllowedOnRestrictedNetworks =
                 ConnectivitySettingsManager.getUidsAllowedOnRestrictedNetworks(mContext);
@@ -2883,8 +2887,9 @@ public class ConnectivityManagerTest {
         // because it has been just installed to device. In case the uid is existed in setting
         // mistakenly, try to remove the uid and set correct uids to setting.
         originalUidsAllowedOnRestrictedNetworks.remove(uid);
-        ConnectivitySettingsManager.setUidsAllowedOnRestrictedNetworks(mContext,
-                originalUidsAllowedOnRestrictedNetworks);
+        runWithShellPermissionIdentity(() ->
+                ConnectivitySettingsManager.setUidsAllowedOnRestrictedNetworks(
+                        mContext, originalUidsAllowedOnRestrictedNetworks), NETWORK_SETTINGS);
 
         final Handler h = new Handler(Looper.getMainLooper());
         final TestableNetworkCallback testNetworkCb = new TestableNetworkCallback();
@@ -2931,8 +2936,9 @@ public class ConnectivityManagerTest {
             final Set<Integer> newUidsAllowedOnRestrictedNetworks =
                     new ArraySet<>(originalUidsAllowedOnRestrictedNetworks);
             newUidsAllowedOnRestrictedNetworks.add(uid);
-            ConnectivitySettingsManager.setUidsAllowedOnRestrictedNetworks(mContext,
-                    newUidsAllowedOnRestrictedNetworks);
+            runWithShellPermissionIdentity(() ->
+                    ConnectivitySettingsManager.setUidsAllowedOnRestrictedNetworks(
+                            mContext, newUidsAllowedOnRestrictedNetworks), NETWORK_SETTINGS);
             // Wait a while for sending allowed uids on the restricted network to netd.
             // TODD: Have a significant signal to know the uids has been send to netd.
             assertBindSocketToNetworkSuccess(network);
@@ -2941,8 +2947,9 @@ public class ConnectivityManagerTest {
             agent.unregister();
 
             // Restore setting.
-            ConnectivitySettingsManager.setUidsAllowedOnRestrictedNetworks(mContext,
-                    originalUidsAllowedOnRestrictedNetworks);
+            runWithShellPermissionIdentity(() ->
+                    ConnectivitySettingsManager.setUidsAllowedOnRestrictedNetworks(
+                            mContext, originalUidsAllowedOnRestrictedNetworks), NETWORK_SETTINGS);
         }
     }
 }