The default memory allocation operator, ::operator new(std::size_t)
, will throw throws a std::bad_alloc
exception if the allocation fails. Therefore, you need not check whether calling ::operator new(std::size_t)
results in nullptr. The nonthrowing form, ::operator new(std::size_t, const std::nothrow_t &)
, will does not throw an exception if the allocation fails , but will instead return returns nullptr
. The same behaviors apply for the operator new[]
versions of both allocation functions. Additionally, the default allocator object (std::allocator
) uses ::operator new(std::size_t)
to perform allocations , and should be treated similarly.
Code Block |
---|
T *p1 = new T; // Throws std::bad_alloc if allocation fails. T *p2 = new (std::nothrow) T; // Returns nullptr if allocation fails. T *p3 = new T[1]; // Throws std::bad_alloc if the allocation fails. T *p4 = new (std::nothrow) T[1]; // Returns nullptr if the allocation fails. |
In additionFurthermore, operator new[]
can throw an error of type std::bad_array_new_length
if , a subclass of std::bad_alloc
, if the size
argument passed to new
is negative or excessively large. This is a subclass of std::bad_alloc
.
When using the nonthrowing form, it is imperative to check that the return value is not nullptr
before accessing the resulting pointer. When using either form, be sure to comply with ERR30ERR50-CPP. Do not call std::terminate(), std::abort(), or std::_Exit()abruptly terminate the program.
Noncompliant Code Example
In this noncompliant code example, an array of int
is created using ::operator new[](std::size_t)
, but and the results of the allocation are not checked. Since the The function is marked as noexcept
, so the caller assumes this function does not throw any exceptions. Because ::operator new[](std::size_t)
can throw an exception if the allocation fails, this it could lead to abnormal termination of the program.
Code Block | ||||
---|---|---|---|---|
| ||||
#include <cstring> void f(const int *array, std::size_t size) noexcept { int *copy = new int[size]; std::memcpy(copy, array, size * sizeof(*copy)); // ... delete [] copy; } |
Compliant Solution (std::nothrow
)
When using std::nothrow
, the new
operator returns either a null pointer or a pointer to the allocated space. Always test the returned pointer to ensure it is not nullptr
before referencing the pointer. This compliant solution handles the error condition appropriately when the returned pointer is nullptr.
Code Block | ||||
---|---|---|---|---|
| ||||
#include <cstring>
#include <new>
void f(const int *array, std::size_t size) noexcept {
int *copy = new (std::nothrow) int[size];
if (!copy) {
// Handle error
return;
}
std::memcpy(copy, array, size * sizeof(*copy));
// ...
delete [] copy;
} |
Compliant Solution (std::bad_alloc
)
Alternatively, one you can use ::operator new[]
without std::nothrow
, and instead catch a std::bad_alloc
exception if sufficient memory cannot be allocated.
Code Block | ||||
---|---|---|---|---|
| ||||
#include <cstring> #include <new> void f(const int *array, std::size_t size) noexcept { int *copy; try { copy = new int[size]; } catch(std::bad_alloc) { // Handle error return; } // At this point, copy has been initialized to allocated memory. std::memcpy(copy, array, size * sizeof(*copy)); // ... delete [] copy; } |
Compliant Solution (noexcept(false))
If the design of the function is such that the caller is expected to handle exceptional situations, it is permissible to mark the function explicitly as one that may throw, as in this compliant solution. This Marking the function is not strictly required, as any function without a noexcept
specifier is presumed to allow throwing.
Code Block | ||||
---|---|---|---|---|
| ||||
#include <cstring> void f(const int *array, std::size_t size) noexcept(false) { int *copy = new int[size]; // If the allocation fails, it will throw an exception which the caller // will have to handle. std::memcpy(copy, array, size * sizeof(*copy)); // ... delete [] copy; } |
Noncompliant Code Example
In this noncompliant code example, two memory allocations are performed within the same expression. Because the memory allocations are passed as arguments to a function call, an exception thrown as a result of one of the calls to new
could result in a memory leak.
Code Block | ||||
---|---|---|---|---|
| ||||
struct A { /* ... */ }; struct B { /* ... */ }; void g(A *, B *); void f() { g(new A, new B); } |
Consider the situation where in which A
is allocated and constructed first, and then B
is allocated and throws an exception. Wrapping the call to g()
in a try
/catch
block is insufficient because it would be impossible to free the memory allocated for A
.
This noncompliant code example also violates EXP50-CPP. Do not depend on the order of evaluation for side effects, because the order in which the arguments to g()
are evaluated is unspecified.
Compliant Solution (std::unique_ptr
)
In this compliant solution, a std::unique_ptr
is used to manage the resources for the A
and B
objects with RAII. In the situation described by the noncompliant code example, B
throwing an exception would still result in the destruction and deallocation of the A
object when then std::unique_ptr<A>
was destroyed.
Code Block | ||||
---|---|---|---|---|
| ||||
#include <memory> struct A { /* ... */ }; struct B { /* ... */ }; void g(std::unique_ptr<A> a, std::unique_ptr<B> b); void f() { g(std::make_unique<A>(), std::make_unique<B>()); } |
Compliant Solution (References)
When possible, the more resilient compliant solution is to remove the memory allocation entirely , and pass the objects by reference instead:.
Code Block | ||||
---|---|---|---|---|
| ||||
struct A { /* ... */ }; struct B { /* ... */ }; void g(A &a, B &b); void f() { A a; B b; g(a, b); } |
Risk Assessment
Failing to detect allocation failures can lead to abnormal program termination and denial-of-service attacks.
If the vulnerable program references memory offset from the return value, an attacker can exploit the program to read or write arbitrary memory. This vulnerability has been used to execute arbitrary code [VU#159523].
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
---|
MEM52-CPP | High | Likely | Medium | P18 | L1 |
Automated Detection
Tool | Version | Checker | Description |
---|
Compass/ROSE |
Coverity | 7.5 | CHECKED_RETURN | Finds inconsistencies in how function call return values are handled | ||||||
Helix QAC |
| C++3225, C++3226, C++3227, C++3228, C++3229, C++4632 | |||||||
Klocwork |
| NPD.CHECK.CALL.MIGHT NPD.CHECK.CALL.MUST NPD.CHECK.MIGHT NPD.CHECK.MUST NPD.CONST.CALL NPD.CONST.DEREF NPD.FUNC.CALL.MIGHT NPD.FUNC.CALL.MUST NPD.FUNC.MIGHT NPD.FUNC.MUST NPD.GEN.CALL.MIGHT NPD.GEN.CALL.MUST NPD.GEN. |
MIGHT NPD.GEN.MUST RNPD.CALL RNPD.DEREF | |||||||||
LDRA tool suite |
| 45 D | Partially implemented | ||||||
Parasoft C/C++test |
| CERT_CPP-MEM52-a | Check the return value of new | ||||||
Parasoft Insure++ | Runtime detection | ||||||||
Polyspace Bug Finder |
| CERT C++: MEM52-CPP | Checks for unprotected dynamic memory allocation (rule partially covered) | ||||||
PVS-Studio |
| V522, V668 |
Related Vulnerabilities
The vulnerability in Adobe Flash [VU#159523] arises because Flash neglects to check the return value from calloc()
. Even though calloc()
returns NULL
, Flash does not attempt to read or write to the return value. Instead, but rather it attempts to write to an offset from the return value. Dereferencing NULL
usually results in a program crash, but dereferencing an offset from NULL
allows an exploit to succeed without crashing the program.
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
SEI CERT C |
Coding Standard | ERR33-C. Detect and handle standard library errors |
MITRE CWE | CWE 252, Unchecked Return Value |
Bibliography
[ISO/IEC 9899:2011] | Subclause 7.20.3, "Memory Management Functions" |
[ISO/IEC 14882-2014] | Subclause 18.6.1.1, "Single- |
Object Forms" |
[ |
Meyers 1996] |
Item 7 |
, " |
Be Prepared for Out-of- |
Memory Conditions" |
[Seacord |
2013] | Chapter 4, "Dynamic Memory Management" |
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