1 files changed, 100 insertions, 0 deletions
diff --git a/errorprone/java/com/google/errorprone/bugpatterns/android/ContextUserIdChecker.java b/errorprone/java/com/google/errorprone/bugpatterns/android/ContextUserIdChecker.java
new file mode 100644
index 000000000000..7f2cce6ea7f0
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+++ b/errorprone/java/com/google/errorprone/bugpatterns/android/ContextUserIdChecker.java
@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.bugpatterns.android;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.matchers.Matchers.enclosingClass;
+import static com.google.errorprone.matchers.Matchers.hasAnnotation;
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static com.google.errorprone.matchers.Matchers.methodInvocation;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.Tree;
+import com.sun.tools.javac.code.Symbol.VarSymbol;
+
+import java.util.List;
+import java.util.Locale;
+import java.util.function.Predicate;
+
+/**
+ * To avoid an explosion of {@code startActivityForUser} style methods, we've
+ * converged on recommending the use of {@code Context.createContextAsUser()},
+ * and then ensuring that all system services pass {@link Context.getUserId()}
+ * for any {@code int userId} arguments across Binder interfaces.
+ * <p>
+ * This design allows developers to easily redirect all services obtained from a
+ * specific {@code Context} to a different user with no additional API surface.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    name = "AndroidFrameworkContextUserId",
+    summary = "Verifies that system_server calls use Context.getUserId()",
+    severity = WARNING)
+public final class ContextUserIdChecker extends BugChecker implements MethodInvocationTreeMatcher {
+    private static final Matcher<Tree> INSIDE_MANAGER =
+            enclosingClass(hasAnnotation("android.annotation.SystemService"));
+
+    private static final Matcher<ExpressionTree> BINDER_CALL = methodInvocation(
+            instanceMethod().onDescendantOf("android.os.IInterface").withAnyName());
+    private static final Matcher<ExpressionTree> GET_USER_ID_CALL = methodInvocation(
+            instanceMethod().onDescendantOf("android.content.Context").named("getUserId"));
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+        if (INSIDE_MANAGER.matches(tree, state)
+                && BINDER_CALL.matches(tree, state)) {
+            final List<VarSymbol> vars = ASTHelpers.getSymbol(tree).params();
+            for (int i = 0; i < vars.size(); i++) {
+                if (USER_ID_VAR.test(vars.get(i)) &&
+                        !GET_USER_ID_CALL.matches(tree.getArguments().get(i), state)) {
+                    return buildDescription(tree)
+                            .setMessage("Must pass Context.getUserId() as user ID"
+                                    + "to enable createContextAsUser()")
+                            .build();
+                }
+            }
+        }
+        return Description.NO_MATCH;
+    }
+
+    private static final UserIdMatcher USER_ID_VAR = new UserIdMatcher();
+
+    private static class UserIdMatcher implements Predicate<VarSymbol> {
+        @Override
+        public boolean test(VarSymbol t) {
+            if ("int".equals(t.type.toString())) {
+                switch (t.name.toString().toLowerCase(Locale.ROOT)) {
+                    case "user":
+                    case "userid":
+                    case "userhandle":
+                    case "user_id":
+                        return true;
+                }
+            }
+            return false;
+        }
+    }
+}