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Fix ASAN detected new/delete mismatches

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The unique_ptr_slab variation of the std::unique_ptr<T> addresses the
issue of new/delete mismatches in code that allocates a _memory slab_
with the global _operator_ new but de-allocates an _object_ with a
delete _expression_.  The use case that manifests the mismatch is as
follows: Allocate a slab of memory that has a C struct at the head of
the slab, with a "my_type mt[0];" as the head's last member.  The slab
is cast to the type of the C struct, but sized to contain N my_type
items.

The object based de-allocation is the behavior of the
std::default_delete<T> template; it is used by the std::unique_ptr<T>
if the user does not specify an alternative deleter.  The
unique_ptr_slab resolves the mismatch with an alternative deleter that
de-allocates the _memory slab_ with the global _operator_ delete.

Signed-off-by: Mark Deric <jmark@openvpn.net>
This commit is contained in:
Mark Deric 2021-10-20 10:06:31 -07:00 committed by David Sommerseth
parent 313426a8cd
commit 6bb4e9c7be
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1 changed files with 31 additions and 0 deletions
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31
openvpn/common/uniqueptr.hpp
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@ -24,10 +24,41 @@
#include <memory>
#include <functional>
#include <type_traits>
namespace openvpn {
template<typename T>
using unique_ptr_del = std::unique_ptr<T, std::function<void(T*)>>;
// The unique_ptr_slab variation of the std::unique_ptr<T> addresses the issue of
// new/delete mismatches in code that allocates a _memory slab_ with the global
// _operator_ new but de-allocates an _object_ with a delete _expression_. The use
// case that manifests the mismatch is as follows: Allocate a slab of memory that has
// a C struct at the head of the slab, with a "my_type mt[0];" as the head's last
// member. The slab is cast to the type of the C struct, but sized to contain N
// my_type items.
//
// The object based de-allocation is the behavior of the std::default_delete<T>
// template; it is used by the std::unique_ptr<T> if the user does not specify an
// alternative deleter. The unique_ptr_slab resolves the mismatch with an alternative
// deleter that de-allocates the _memory slab_ with the global _operator_ delete.
template<typename T>
void delete_slab(T* ptr) {
::operator delete(const_cast<typename std::remove_cv<T>::type*>(ptr));
}
template<typename T>
class slab_deleter
{
public:
slab_deleter() {}
void operator()(T* ptr){
delete_slab(ptr);
}
};
template<typename T>
using unique_ptr_slab = std::unique_ptr<T, slab_deleter<T>>;
}
#endif