[security][CVE-2018-6337] Flush folly::secureRandom buffer on fork

fredemmott · fredemmott · commit e2d10a1e32d0 · 2018-05-24T10:39:15.000-07:00
D8109884 D8110240 CVE-2018-6337
diff --git a/patches/folly-CVE-2018-6337.patch b/patches/folly-CVE-2018-6337.patch
@@ -0,0 +1,111 @@
+diff --git a/third-party/folly/src/folly/Random.cpp b/third-party/folly/src/folly/Random.cpp
+index afb62f5d..40a6b17f 100644
+--- a/third-party/folly/src/folly/Random.cpp
++++ b/third-party/folly/src/folly/Random.cpp
+@@ -72,6 +72,7 @@ void readRandomDevice(void* data, size_t size) {
+ 
+ class BufferedRandomDevice {
+  public:
++  static once_flag flag;
+   static constexpr size_t kDefaultBufferSize = 128;
+ 
+   explicit BufferedRandomDevice(size_t bufferSize = kDefaultBufferSize);
+@@ -97,10 +98,28 @@ class BufferedRandomDevice {
+   unsigned char* ptr_;
+ };
+ 
++once_flag BufferedRandomDevice::flag;
++struct RandomTag {};
++
+ BufferedRandomDevice::BufferedRandomDevice(size_t bufferSize)
+   : bufferSize_(bufferSize),
+     buffer_(new unsigned char[bufferSize]),
+     ptr_(buffer_.get() + bufferSize) {  // refill on first use
++  call_once(flag, [this]() {
++    detail::AtFork::registerHandler(
++        this,
++        /*prepare*/ []() { return true; },
++        /*parent*/ []() {},
++        /*child*/
++        []() {
++          using Single = SingletonThreadLocal<BufferedRandomDevice, RandomTag>;
++          auto& t = Single::get();
++          // Clear out buffered data on fork.
++          //
++          // Ensure child and parent do not share same entropy pool.
++          t.ptr_ = t.buffer_.get() + t.bufferSize_;
++        });
++  });
+ }
+ 
+ void BufferedRandomDevice::getSlow(unsigned char* data, size_t size) {
+@@ -124,8 +143,6 @@ void BufferedRandomDevice::getSlow(unsigned char* data, size_t size) {
+   ptr_ += size;
+ }
+ 
+-struct RandomTag {};
+-
+ } // namespace
+ 
+ void Random::secureRandom(void* data, size_t size) {
+diff --git a/third-party/folly/src/folly/detail/AtFork.cpp b/third-party/folly/src/folly/detail/AtFork.cpp
+index 48c42fd3..12a6f934 100644
+--- a/third-party/folly/src/folly/detail/AtFork.cpp
++++ b/third-party/folly/src/folly/detail/AtFork.cpp
+@@ -13,12 +13,14 @@
+  * See the License for the specific language governing permissions and
+  * limitations under the License.
+  */
++
+ #include <folly/detail/AtFork.h>
+ 
+ #include <list>
+ #include <mutex>
+ 
+-#include <folly/Exception.h>
++#include <folly/lang/Exception.h>
++#include <folly/portability/PThread.h>
+ 
+ namespace folly {
+ 
+@@ -72,7 +74,10 @@ class AtForkList {
+ #if FOLLY_HAVE_PTHREAD_ATFORK
+     int ret = pthread_atfork(
+         &AtForkList::prepare, &AtForkList::parent, &AtForkList::child);
+-    checkPosixError(ret, "pthread_atfork failed");
++    if (ret != 0) {
++      throw_exception<std::system_error>(
++          ret, std::generic_category(), "pthread_atfork failed");
++    }
+ #elif !__ANDROID__ && !defined(_MSC_VER)
+ // pthread_atfork is not part of the Android NDK at least as of n9d. If
+ // something is trying to call native fork() directly at all with Android's
+diff --git a/third-party/folly/src/folly/test/RandomTest.cpp b/third-party/folly/src/folly/test/RandomTest.cpp
+index 9c33159b..2ee74c6d 100644
+--- a/third-party/folly/src/folly/test/RandomTest.cpp
++++ b/third-party/folly/src/folly/test/RandomTest.cpp
+@@ -138,3 +138,24 @@ TEST(Random, sanity) {
+         std::unordered_set<uint64_t>(vals.begin(), vals.end()).size());
+   }
+ }
++
++TEST(Random, SecureFork) {
++  unsigned char buffer = 0;
++  // Init random buffer
++  folly::Random::secureRandom(&buffer, 1);
++
++  auto pid = fork();
++  EXPECT_NE(pid, -1);
++  if (pid) {
++    // parent
++    int status = 0;
++    folly::Random::secureRandom(&buffer, 1);
++    auto pid2 = wait(&status);
++    EXPECT_NE(WEXITSTATUS(status), buffer);
++    EXPECT_EQ(pid, pid2);
++  } else {
++    // child
++    folly::Random::secureRandom(&buffer, 1);
++    exit(buffer); // Do not print gtest results
++  }
++}
