1 files changed, 130 insertions, 0 deletions
diff --git a/libs/binder/tests/binderClearBufTest.cpp b/libs/binder/tests/binderClearBufTest.cpp
new file mode 100644
index 0000000000..2d30c8da45
--- /dev/null
+++ b/libs/binder/tests/binderClearBufTest.cpp
@@ -0,0 +1,130 @@
+/*
+ * 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.
+ */
+
+#include <android-base/logging.h>
+#include <binder/Binder.h>
+#include <binder/IBinder.h>
+#include <binder/IPCThreadState.h>
+#include <binder/IServiceManager.h>
+#include <binder/Parcel.h>
+#include <binder/Stability.h>
+#include <gtest/gtest.h>
+
+#include <sys/prctl.h>
+#include <thread>
+
+using namespace android;
+
+const String16 kServerName = String16("binderClearBuf");
+
+std::string hexString(const void* bytes, size_t len) {
+    if (bytes == nullptr) return "<null>";
+
+    const uint8_t* bytes8 = static_cast<const uint8_t*>(bytes);
+    char chars[] = "0123456789abcdef";
+    std::string result;
+    result.resize(len * 2);
+
+    for (size_t i = 0; i < len; i++) {
+        result[2 * i] = chars[bytes8[i] >> 4];
+        result[2 * i + 1] = chars[bytes8[i] & 0xf];
+    }
+
+    return result;
+}
+
+class FooBar : public BBinder {
+ public:
+    enum {
+        TRANSACTION_REPEAT_STRING = IBinder::FIRST_CALL_TRANSACTION,
+    };
+
+    std::mutex foo;
+    std::string last;
+
+    status_t onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) {
+        // not checking data, since there is no hook at the time this test is
+        // written to check values there are set to zero. Instead, we only check
+        // the reply parcel.
+
+        switch (code) {
+            case TRANSACTION_REPEAT_STRING: {
+                const char* str = data.readCString();
+                return reply->writeCString(str == nullptr ? "<null>" : str);
+            }
+        }
+        return BBinder::onTransact(code, data, reply, flags);
+    }
+    static std::string RepeatString(const sp<IBinder> binder,
+                                    const std::string& repeat,
+                                    std::string* outBuffer) {
+        Parcel data;
+        data.writeCString(repeat.c_str());
+        std::string result;
+        const uint8_t* lastReply;
+        size_t lastReplySize;
+        {
+            Parcel reply;
+            binder->transact(TRANSACTION_REPEAT_STRING, data, &reply, FLAG_CLEAR_BUF);
+            result = reply.readCString();
+            lastReply = reply.data();
+            lastReplySize = reply.dataSize();
+        }
+        *outBuffer = hexString(lastReply, lastReplySize);
+        return result;
+    }
+};
+
+TEST(BinderClearBuf, ClearKernelBuffer) {
+    sp<IBinder> binder = defaultServiceManager()->getService(kServerName);
+    ASSERT_NE(nullptr, binder);
+
+    std::string replyBuffer;
+    std::string result = FooBar::RepeatString(binder, "foo", &replyBuffer);
+    EXPECT_EQ("foo", result);
+
+    // the buffer must have at least some length for the string, but we will
+    // just check it has some length, to avoid assuming anything about the
+    // format
+    EXPECT_GT(replyBuffer.size(), 0);
+
+    for (size_t i = 0; i < replyBuffer.size(); i++) {
+        EXPECT_EQ(replyBuffer[i], '0') << "reply buffer at " << i;
+    }
+}
+
+int main(int argc, char** argv) {
+    ::testing::InitGoogleTest(&argc, argv);
+
+    if (fork() == 0) {
+        prctl(PR_SET_PDEATHSIG, SIGHUP);
+
+        sp<IBinder> server = new FooBar;
+        android::defaultServiceManager()->addService(kServerName, server);
+
+        IPCThreadState::self()->joinThreadPool(true);
+        exit(1);  // should not reach
+    }
+
+    // This is not racey. Just giving these services some time to register before we call
+    // getService which sleeps for much longer. One alternative would be to
+    // start a threadpool + use waitForService, but we want to have as few
+    // binder things going on in this test as possible, since we are checking
+    // memory is zero'd which the kernel has a right to change.
+    usleep(100000);
+
+    return RUN_ALL_TESTS();
+}