Fix write-heap-buffer-overflow in copy_out

Differential Revision: D80885980

Pull Request resolved: #15584

Author: lucylq

kernels/portable/cpu/op_copy.cpp

@@ -49,7 +49,8 @@ Tensor& copy_out(
   // Use direct copy fast path if broadcast is not needed and tensors are
   // non-empty
   if (internal::sizes_match_ignoring_leading_1s(out.sizes(), src.sizes()) &&
-      src.numel() > 0) {
+      src.numel() > 0 && out.nbytes() >= src.nbytes() &&
+      tensors_have_same_dtype(src, out)) {
     std::memcpy(out.mutable_data_ptr(), src.const_data_ptr(), src.nbytes());
   } else {
     ET_SWITCH_REALHBBF16_TYPES(in.scalar_type(), ctx, op_name, CTYPE, [&]() {
@@ -91,8 +92,9 @@ Tensor& copy_(
   // Use direct copy fast path if broadcast is not needed and tensors are
   // non-empty
   if (internal::sizes_match_ignoring_leading_1s(in.sizes(), src.sizes()) &&
-      src.numel() > 0) {
-    std::memcpy(in.mutable_data_ptr(), src.const_data_ptr(), in.nbytes());
+      src.numel() > 0 && in.nbytes() >= src.nbytes() &&
+      tensors_have_same_dtype(src, in)) {
+    std::memcpy(in.mutable_data_ptr(), src.const_data_ptr(), src.nbytes());
   } else {
     ET_SWITCH_REALHBBF16_TYPES(in.scalar_type(), ctx, op_name, CTYPE, [&]() {
       utils::apply_bitensor_elementwise_fn<