Check FLAG_CLEAR_BUF behavior.

This checks that the kernel actually clears the buffer space for a reply
parcel as requested. No check is made that the deallocated memory
is also cleared since it is deallocated, and we have no control over
what happens to it. Ramdumps should be used to verify use of this flag,
but this test is a basic sanity check for them. In the future, we could
consider expanding this by adding something like libhwbinder's
postCommandTask here. However, for now, avoiding overhead for test only.

Bug: 171501998
Test: binderClearBufTest
Change-Id: I797a9e9b6a9b8c70816ce51bb9bc22f518b54f77

3 files changed, 152 insertions, 0 deletions

diff --git a/libs/binder/TEST_MAPPING b/libs/binder/TEST_MAPPING
index 97e282e783..00a14f408d 100644
--- a/libs/binder/TEST_MAPPING
+++ b/libs/binder/TEST_MAPPING
@@ -10,6 +10,9 @@
       "name": "binderAllocationLimits"
     },
     {
+      "name": "binderClearBufTest"
+    },
+    {
       "name": "binderDriverInterfaceTest"
     },
     {
diff --git a/libs/binder/tests/Android.bp b/libs/binder/tests/Android.bp
index 87f1d45350..988f7f3c6d 100644
--- a/libs/binder/tests/Android.bp
+++ b/libs/binder/tests/Android.bp
@@ -157,6 +157,24 @@ cc_test {
     require_root: true,
 }
 
+cc_test {
+    name: "binderClearBufTest",
+    defaults: ["binder_test_defaults"],
+    srcs: [
+        "binderClearBufTest.cpp",
+    ],
+
+    shared_libs: [
+        "libbase",
+        "libbinder",
+        "liblog",
+        "libutils",
+    ],
+
+    test_suites: ["general-tests"],
+    require_root: true,
+}
+
 aidl_interface {
     name: "binderStabilityTestIface",
     unstable: true,
diff --git a/libs/binder/tests/binderClearBufTest.cpp b/libs/binder/tests/binderClearBufTest.cpp
new file mode 100644
index 0000000000..a565e72091
--- /dev/null
+++ b/libs/binder/tests/binderClearBufTest.cpp
@@ -0,0 +1,131 @@
+/*
+ * 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();
+        }
+        IPCThreadState::self()->flushCommands();
+        *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();
+}