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/*
* Copyright (C) 2012 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.android.tools.lint.checks;
import com.android.annotations.NonNull;
import com.android.annotations.Nullable;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.ClassContext;
import com.android.tools.lint.detector.api.Detector;
import com.android.tools.lint.detector.api.Detector.ClassScanner;
import com.android.tools.lint.detector.api.Issue;
import com.android.tools.lint.detector.api.LintUtils;
import com.android.tools.lint.detector.api.Scope;
import com.android.tools.lint.detector.api.Severity;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.InsnList;
import org.objectweb.asm.tree.MethodInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.analysis.Analyzer;
import org.objectweb.asm.tree.analysis.AnalyzerException;
import org.objectweb.asm.tree.analysis.BasicInterpreter;
import org.objectweb.asm.tree.analysis.BasicValue;
import org.objectweb.asm.tree.analysis.Frame;
import java.util.Collections;
import java.util.List;
/**
* Checks for hardcoded seeds with random numbers.
*/
public class SecureRandomDetector extends Detector implements ClassScanner {
/** Unregistered activities and services */
public static final Issue ISSUE = Issue.create(
"SecureRandom", //$NON-NLS-1$
"Looks for suspicious usage of the SecureRandom class",
"Specifying a fixed seed will cause the instance to return a predictable sequence " +
"of numbers. This may be useful for testing but it is not appropriate for secure use.",
Category.PERFORMANCE,
9,
Severity.WARNING,
SecureRandomDetector.class,
Scope.CLASS_FILE_SCOPE).
setMoreInfo("http://developer.android.com/reference/java/security/SecureRandom.html");
private static final String SET_SEED = "setSeed"; //$NON-NLS-1$
private static final String OWNER_SECURE_RANDOM = "java/security/SecureRandom"; //$NON-NLS-1$
private static final String OWNER_RANDOM = "java/util/Random"; //$NON-NLS-1$
private static final String VM_SECURE_RANDOM = 'L' + OWNER_SECURE_RANDOM + ';';
/** Method description for a method that takes a long argument (no return type specified */
private static final String LONG_ARG = "(J)"; //$NON-NLS-1$
/** Constructs a new {@link SecureRandomDetector} */
public SecureRandomDetector() {
}
// ---- Implements ClassScanner ----
@Override
@Nullable
public List<String> getApplicableCallNames() {
return Collections.singletonList(SET_SEED);
}
@Override
public void checkCall(@NonNull ClassContext context, @NonNull ClassNode classNode,
@NonNull MethodNode method, @NonNull MethodInsnNode call) {
String owner = call.owner;
String desc = call.desc;
if (owner.equals(OWNER_SECURE_RANDOM)) {
if (desc.startsWith(LONG_ARG)) {
checkValidSetSeed(context, call);
} else if (desc.startsWith("([B)")) { //$NON-NLS-1$
// setSeed(byte[]) ...
// We could do some flow analysis here to see whether the byte array getting
// passed in appears to be fixed.
// However, people calling this constructor rather than the simpler one
// with a fixed integer are probably less likely to make that mistake... right?
}
} else if (owner.equals(OWNER_RANDOM) && desc.startsWith(LONG_ARG)) {
// Called setSeed(long) on an instanceof a Random object. Flag this if the instance
// is likely a SecureRandom.
// Track allocations such that we know whether the type of the call
// is on a SecureRandom rather than a Random
Analyzer analyzer = new Analyzer(new BasicInterpreter() {
@Override
public BasicValue newValue(Type type) {
if (type != null && type.getDescriptor().equals(VM_SECURE_RANDOM)) {
return new BasicValue(type);
}
return super.newValue(type);
}
});
try {
Frame[] frames = analyzer.analyze(classNode.name, method);
InsnList instructions = method.instructions;
Frame frame = frames[instructions.indexOf(call)];
int stackSlot = frame.getStackSize();
for (Type type : Type.getArgumentTypes(desc)) {
stackSlot -= type.getSize();
}
BasicValue stackValue = (BasicValue) frame.getStack(stackSlot);
Type type = stackValue.getType();
if (type != null && type.getDescriptor().equals(VM_SECURE_RANDOM)) {
checkValidSetSeed(context, call);
}
} catch (AnalyzerException e) {
context.log(e, null);
}
} else if (owner.equals(OWNER_RANDOM) && desc.startsWith(LONG_ARG)) {
// Called setSeed(long) on an instanceof a Random object. Flag this if the instance
// is likely a SecureRandom.
// TODO
}
}
private void checkValidSetSeed(ClassContext context, MethodInsnNode call) {
assert call.name.equals(SET_SEED);
// Make sure the argument passed is not a literal
AbstractInsnNode prev = LintUtils.getPrevInstruction(call);
if (prev == null) {
return;
}
int opcode = prev.getOpcode();
if (opcode == Opcodes.LCONST_0 || opcode == Opcodes.LCONST_1 || opcode == Opcodes.LDC) {
context.report(ISSUE, context.getLocation(call),
"Do not call setSeed() on a SecureRandom with a fixed seed: " +
"it is not secure. Use getSeed().",
null);
} else if (opcode == Opcodes.INVOKESTATIC) {
String methodName = ((MethodInsnNode) prev).name;
if (methodName.equals("currentTimeMillis") || methodName.equals("nanoTime")) {
context.report(ISSUE, context.getLocation(call),
"It is dangerous to seed SecureRandom with the current time because " +
"that value is more predictable to an attacker than the default seed.",
null);
}
}
}
}
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