[RESTRICT AUTOMERGE] Fix potential decrypt srcPtr overflow.

Merged from http://go/wvgerrit/114903

There is a potential integer overflow to bypass the
source base size check in decrypt. The source pointer
can then point to the outside of the source buffer,
which could potentially leak arbitrary memory content
to destination pointer.

Test: sts-tradefed
  sts-tradefed run sts-engbuild-no-spl-lock -m StsHostTestCases --test android.security.sts.Bug_176496160#testPocBug_176496160

Test: push to device with target_hwasan-userdebug build
  adb shell /data/local/tmp/Bug-17649616064

Bug: 176496160
Bug: 176444786
Change-Id: I208e0d5d949e8ef003fcf7d6f129eab66b9b3656

libwvdrmengine/mediacrypto/src_hidl/WVCryptoPlugin.cpp

@@ -152,7 +152,11 @@ Return<void> WVCryptoPlugin::decrypt(
     return Void();
   }
 
-  if (source.offset + offset + source.size > sourceBase->getSize()) {
+  size_t totalSrcSize = 0;
+  if (__builtin_add_overflow(source.offset, offset, &totalSrcSize) ||
+      __builtin_add_overflow(totalSrcSize, source.size, &totalSrcSize) ||
+      totalSrcSize > sourceBase->getSize()) {
+    android_errorWriteLog(0x534e4554, "176496160");
     _hidl_cb(Status::ERROR_DRM_CANNOT_HANDLE, 0, "invalid buffer size");
     return Void();
   }