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/*
* Copyright 2017 The Error Prone Authors.
*
* 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.common.base.MoreObjects.firstNonNull;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.matchers.Matchers.allOf;
import static com.google.errorprone.matchers.Matchers.hasModifier;
import static com.google.errorprone.matchers.Matchers.isSameType;
import static com.google.errorprone.matchers.Matchers.methodHasParameters;
import static com.google.errorprone.matchers.Matchers.methodIsNamed;
import static com.google.errorprone.matchers.Matchers.not;
import static com.google.errorprone.util.ASTHelpers.constValue;
import static com.google.errorprone.util.ASTHelpers.getSymbol;
import static com.google.errorprone.util.ASTHelpers.getType;
import static com.google.errorprone.util.ASTHelpers.isSubtype;
import static com.google.errorprone.util.ASTHelpers.resolveExistingMethod;
import com.google.common.collect.ImmutableList;
import com.google.errorprone.BugPattern;
import com.google.errorprone.BugPattern.StandardTags;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker;
import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matcher;
import com.sun.source.tree.ClassTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.ReturnTree;
import com.sun.source.tree.Tree;
import com.sun.source.util.TreeScanner;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.code.Symbol.TypeSymbol;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.util.FatalError;
import javax.annotation.Nullable;
import javax.lang.model.element.Modifier;
/** @author [email protected] (Emily P.M. Johnston) */
@BugPattern(
name = "FragmentInjection",
summary =
"Classes extending PreferenceActivity must implement isValidFragment such that it does not"
+ " unconditionally return true to prevent vulnerability to fragment injection"
+ " attacks.",
severity = WARNING,
tags = StandardTags.LIKELY_ERROR)
public class FragmentInjection extends BugChecker implements ClassTreeMatcher {
private static final Matcher OVERRIDES_IS_VALID_FRAGMENT =
allOf(methodIsNamed("isValidFragment"), methodHasParameters(isSameType("java.lang.String")));
@Override
public Description matchClass(ClassTree tree, VisitorState state) {
if (!state.isAndroidCompatible()) {
return Description.NO_MATCH;
}
// Only examine classes that extend PreferenceActivity.
Type preferenceActivityType = state.getTypeFromString("android.preference.PreferenceActivity");
if (!isSubtype(getType(tree), preferenceActivityType, state)) {
return NO_MATCH;
}
// Examine each method in the class. Complain if isValidFragment not implemented.
TypeSymbol preferenceActivityTypeSymbol = preferenceActivityType.tsym;
boolean methodNotImplemented = true;
try {
MethodSymbol isValidFragmentMethodSymbol =
resolveExistingMethod(
state,
getSymbol(tree),
state.getName("isValidFragment"),
ImmutableList.of(state.getSymtab().stringType),
ImmutableList.of());
methodNotImplemented = isValidFragmentMethodSymbol.owner.equals(preferenceActivityTypeSymbol);
} catch (FatalError e) {
// If isValidFragment method symbol is not found, then we must be compiling against an old SDK
// version (< 19) in which isValidFragment is not yet implemented, and neither this class nor
// any of its super classes have implemented it.
}
// If neither this class nor any super class besides PreferenceActivity implements
// isValidFragment, and this is not an abstract class, emit warning.
if (methodNotImplemented && not(hasModifier(Modifier.ABSTRACT)).matches(tree, state)) {
return buildDescription(tree)
.setMessage("Class extending PreferenceActivity does not implement isValidFragment.")
.build();
}
// Check the implementation of isValidFragment. Complain if it always returns true.
MethodTree isValidFragmentMethodTree = getMethod(OVERRIDES_IS_VALID_FRAGMENT, tree, state);
if (isValidFragmentMethodTree != null) {
if (isValidFragmentMethodTree.accept(ALWAYS_RETURNS_TRUE, null)) {
return buildDescription(isValidFragmentMethodTree)
.setMessage("isValidFragment unconditionally returns true.")
.build();
}
}
return NO_MATCH;
}
/*
* Return the first method tree on the given class tree that matches the given method matcher,
* or null if one does not exist.
*/
@Nullable
private static MethodTree getMethod(
Matcher methodMatcher, ClassTree classTree, VisitorState state) {
for (Tree member : classTree.getMembers()) {
if (member instanceof MethodTree) {
MethodTree memberTree = (MethodTree) member;
if (methodMatcher.matches(memberTree, state)) {
return memberTree;
}
}
}
return null;
}
/*
* A tree scanner for isValidFragment, accepts methods that return true on all code paths.
*/
private static final TreeScanner ALWAYS_RETURNS_TRUE =
new TreeScanner() {
@Override
public Boolean visitReturn(ReturnTree node, Void unused) {
ExpressionTree returnExpression = node.getExpression();
Boolean returnValue = constValue(returnExpression, Boolean.class);
return firstNonNull(returnValue, false);
}
@Override
public Boolean reduce(Boolean r1, Boolean r2) {
// And together the results of all visits. If any visit was false (return value was false
// or not constant), the method implementation is okay.
// null value means not a return statement, doesn't change anything, so treat as true.
return (r1 == null || r1) && (r2 == null || r2);
}
};
}
