Handle image size overflow

Author: mcheshkov

src/PngImg.cc

@@ -60,10 +60,20 @@ void PngImg::ReadInfo_(PngReadStruct& rs) {
 ///
 void PngImg::InitStorage_() {
     rowPtrs_.resize(info_.height, nullptr);
-    data_ = new png_byte[info_.height * info_.rowbytes];
+    // Extend height and rowbytes from uint32_t to size_t to avoid multiplication overflow when size_t is larger
+    size_t h = info_.height;
+    size_t rb = info_.rowbytes;
+    // We need to make sure that info_.height * info_.rowbytes will not overflow size_t
+    // Unfotunately, there's no simple and portable way to do this in C++
+    // For integer division of positive numbers a * b > c <==> a > c / b holds
+    if (h > std::numeric_limits<size_t>::max() / rb) {
+        // TODO Propagate this exception to JS, and test it
+        throw std::runtime_error("Image is too large to allocate single buffer");
+    }
+    data_ = new png_byte[h * rb];
 
     for(size_t i = 0; i < info_.height; ++i) {
-        rowPtrs_[i] = data_ + i * info_.rowbytes;
+        rowPtrs_[i] = data_ + i * rb;
     }
 }