Prevent integer overflow when processing covr MPEG4 atoms

If the 'chunk_data_size' value is SIZE_MAX, an integer overflow will occur
and cause an undersized buffer to be allocated. The following processing
then overfills the resulting memory and creates a potentially exploitable
condition. Ensure that integer overflow does not occur.

Bug: 20923261
Change-Id: I75cce323aec04a612e5a230ecd7c2077ce06035f
diff --git a/media/libstagefright/MPEG4Extractor.cpp b/media/libstagefright/MPEG4Extractor.cpp
index a2d12a1e..850e6af 100644
--- a/media/libstagefright/MPEG4Extractor.cpp
+++ b/media/libstagefright/MPEG4Extractor.cpp
@@ -1932,6 +1932,10 @@
             if (mFileMetaData != NULL) {
                 ALOGV("chunk_data_size = %lld and data_offset = %lld",
                         chunk_data_size, data_offset);
+
+                if (chunk_data_size >= SIZE_MAX - 1) {
+                    return ERROR_MALFORMED;
+                }
                 sp<ABuffer> buffer = new ABuffer(chunk_data_size + 1);
                 if (mDataSource->readAt(
                     data_offset, buffer->data(), chunk_data_size) != (ssize_t)chunk_data_size) {