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Fix allocation failure during JSON destruction #5239

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Fix allocation failure during JSON destruction #5239

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76 changes: 42 additions & 34 deletions include/nlohmann/json.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -598,50 +598,58 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
}
if (t == value_t::array || t == value_t::object)
{
// flatten the current json_value to a heap-allocated stack
std::vector<basic_json> stack;

// move the top-level items to stack
if (t == value_t::array)
{
stack.reserve(array->size());
std::move(array->begin(), array->end(), std::back_inserter(stack));
}
else
{
stack.reserve(object->size());
for (auto&& it : *object)
{
stack.push_back(std::move(it.second));
}
}

while (!stack.empty())
JSON_TRY
{
// move the last item to a local variable to be processed
basic_json current_item(std::move(stack.back()));
stack.pop_back();
// flatten the current json_value to a heap-allocated stack
std::vector<basic_json> stack;

// if current_item is array/object, move
// its children to the stack to be processed later
if (current_item.is_array())
// move the top-level items to stack
if (t == value_t::array)
{
std::move(current_item.m_data.m_value.array->begin(), current_item.m_data.m_value.array->end(), std::back_inserter(stack));

current_item.m_data.m_value.array->clear();
stack.reserve(array->size());
std::move(array->begin(), array->end(), std::back_inserter(stack));
}
else if (current_item.is_object())
else
{
for (auto&& it : *current_item.m_data.m_value.object)
stack.reserve(object->size());
for (auto&& it : *object)
{
stack.push_back(std::move(it.second));
}

current_item.m_data.m_value.object->clear();
}

// it's now safe that current_item gets destructed
// since it doesn't have any children
while (!stack.empty())
{
// move the last item to a local variable to be processed
basic_json current_item(std::move(stack.back()));
stack.pop_back();

// if current_item is array/object, move
// its children to the stack to be processed later
if (current_item.is_array())
{
std::move(current_item.m_data.m_value.array->begin(), current_item.m_data.m_value.array->end(), std::back_inserter(stack));

current_item.m_data.m_value.array->clear();
}
else if (current_item.is_object())
{
for (auto&& it : *current_item.m_data.m_value.object)
{
stack.push_back(std::move(it.second));
}

current_item.m_data.m_value.object->clear();
}

// it's now safe that current_item gets destructed
// since it doesn't have any children
}
}
JSON_CATCH(...) // LCOV_EXCL_LINE
{
// If the heap-allocated stack cannot grow, fall back to
// recursive destruction rather than escaping a noexcept dtor.
}
}

Expand Down
76 changes: 42 additions & 34 deletions single_include/nlohmann/json.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -21424,50 +21424,58 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
}
if (t == value_t::array || t == value_t::object)
{
// flatten the current json_value to a heap-allocated stack
std::vector<basic_json> stack;

// move the top-level items to stack
if (t == value_t::array)
{
stack.reserve(array->size());
std::move(array->begin(), array->end(), std::back_inserter(stack));
}
else
JSON_TRY
{
stack.reserve(object->size());
for (auto&& it : *object)
{
stack.push_back(std::move(it.second));
}
}
// flatten the current json_value to a heap-allocated stack
std::vector<basic_json> stack;

while (!stack.empty())
{
// move the last item to a local variable to be processed
basic_json current_item(std::move(stack.back()));
stack.pop_back();

// if current_item is array/object, move
// its children to the stack to be processed later
if (current_item.is_array())
// move the top-level items to stack
if (t == value_t::array)
{
std::move(current_item.m_data.m_value.array->begin(), current_item.m_data.m_value.array->end(), std::back_inserter(stack));

current_item.m_data.m_value.array->clear();
stack.reserve(array->size());
std::move(array->begin(), array->end(), std::back_inserter(stack));
}
else if (current_item.is_object())
else
{
for (auto&& it : *current_item.m_data.m_value.object)
stack.reserve(object->size());
for (auto&& it : *object)
{
stack.push_back(std::move(it.second));
}

current_item.m_data.m_value.object->clear();
}

// it's now safe that current_item gets destructed
// since it doesn't have any children
while (!stack.empty())
{
// move the last item to a local variable to be processed
basic_json current_item(std::move(stack.back()));
stack.pop_back();

// if current_item is array/object, move
// its children to the stack to be processed later
if (current_item.is_array())
{
std::move(current_item.m_data.m_value.array->begin(), current_item.m_data.m_value.array->end(), std::back_inserter(stack));

current_item.m_data.m_value.array->clear();
}
else if (current_item.is_object())
{
for (auto&& it : *current_item.m_data.m_value.object)
{
stack.push_back(std::move(it.second));
}

current_item.m_data.m_value.object->clear();
}

// it's now safe that current_item gets destructed
// since it doesn't have any children
}
}
JSON_CATCH(...) // LCOV_EXCL_LINE
{
// If the heap-allocated stack cannot grow, fall back to
// recursive destruction rather than escaping a noexcept dtor.
}
}

Expand Down
60 changes: 60 additions & 0 deletions tests/src/unit-regression2.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,9 @@ using ordered_json = nlohmann::ordered_json;
#endif

#include <cstdio>
#include <cstdlib>
#include <list>
#include <new>
#include <type_traits>
#include <utility>

Expand Down Expand Up @@ -91,6 +93,49 @@ DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")

using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;

#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)
namespace
{
bool fail_next_global_allocation = false;

void* checked_malloc(std::size_t size)
{
if (fail_next_global_allocation)
{
fail_next_global_allocation = false;
throw std::bad_alloc();
}

if (void* const result = std::malloc(size))
{
return result;
}

throw std::bad_alloc();
}
} // namespace

void* operator new (std::size_t size)
{
return checked_malloc(size);
}

void* operator new[](std::size_t size)
{
return checked_malloc(size);
}

void operator delete (void* ptr) noexcept
{
std::free(ptr);
}

void operator delete[](void* ptr) noexcept
{
std::free(ptr);
}
#endif

/////////////////////////////////////////////////////////////////////
// for #1647
/////////////////////////////////////////////////////////////////////
Expand Down Expand Up @@ -1454,4 +1499,19 @@ TEST_CASE("issue #4320 - custom base class must not leak nlohmann::detail into A
CHECK(j == json({{"x", 1.0}, {"y", 2.0}, {"z", 3.0}}));
}

#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)
TEST_CASE("regression test #5135 - destructor tolerates stack allocation failure")
{
{
json j = json::array({json::array({1, 2}), json::object({{"key", json::array({3})}})});
fail_next_global_allocation = true;
}

const bool allocation_failure_was_injected = !fail_next_global_allocation;
fail_next_global_allocation = false;

CHECK(allocation_failure_was_injected);
}
#endif

DOCTEST_CLANG_SUPPRESS_WARNING_POP
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