Page History

The default memory allocation operator, ::operator new(std::size_t), 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 &), does not throw an exception if the allocation fails but instead 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.

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[

The return values for memory allocation routines indicate the failure or success of the allocation. According to C99, {{calloc()}}, {{malloc()}}, and {{realloc()}} return null pointers if the requested memory allocation fails \[[ISO/IEC 9899:1999|AA. References#ISO/IEC 9899-1999]\]. Failure to detect and properly handle memory management errors can lead to unpredictable and unintended program behavior. As a result, it is necessary to check the final status of memory management routines and handle errors appropriately and in accordance with [ERR00-CPP. Adopt and implement a consistent and comprehensive error-handling policy].

By default operator new will throw a std::bad_alloc exception if the allocation fails. Therefore you need not check that the result of operator new is NULL. However, to ease conversion of code to C++, the C++ Standard ISO/IEC 14882-2003 provides a variant of operator new that behaves like malloc():

int* s = new int[-1]; // throwsThrows a std::bad_alloc exception
int* s  if the allocation fails
T *p4 = new (std::nothrow) intT[-1]; // returns NULL
 Returns nullptr if the allocation fails

Furthermore, operator new[] can throw an error of type std::bad_array_new_length, a subclass of std::bad_alloc, if the size argument passed to new is negative or excessively large.

When using the nonthrowing formWhen using std::nothrow, it is imperative to check that the return value is not NULL before using it.

The following table shows the possible outcomes of the C++ Standard Library memory allocation functions.

...

nullptr before accessing the resulting pointer. When using either form, be sure to comply with ERR50-CPP. Do not abruptly terminate the program.

Noncompliant Code Example

In this noncompliant code example, an array of int is created using ::operator new[](std::size_t) and the results of the allocation are not checked. 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, it could lead to abnormal termination of the program

Noncompliant Code Example (malloc())

In this example, array is copied into dynamically allocated memory referenced by copy. However, the result of malloc() is not checked before copy is referenced. Consequently, if malloc() fails, the program abnormally terminates.

#include <cstring>
 
void f(const int *array, std::size_t size) noexcept {
  int * copy = new (int*)std::malloc(size * sizeof *copy)int[size];
  std::memcpy(copy, array, size * sizeof (*copy));
  // ...
  delete [] free(copy);
}

...

Compliant Solution (std::nothrow)

This example remains noncompliant if we replace malloc() with new(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.

#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)

With Alternatively, you can use ::operator new[] without 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 NULL before referencing the pointer. Handle the error condition appropriately when the returned pointer is NULL and instead catch a std::bad_alloc exception if sufficient memory cannot be allocated.

int#include <cstring>
#include <new>
 
void f(const int * array, std::size_t size) noexcept {
  int * constcopy;
  try {
    copy = new(std::nothrow) int[size];
  if} (copy == NULLcatch(std::bad_alloc) {
    // IndicateHandle error to caller.
    return -1;
  }
  // At this point, copy has been initialized to allocated memory
  std::memcpy(copy, array, size * sizeof (*copy));
  // ...
  delete [] copy;

  // Indicate successful completion.
  return 0;
}

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. Marking the function is not strictly required, as any function without a noexcept specifier is presumed to allow throwingAlternatively, one can use operator new without std::nothrow. Unless std::nothrow is provided, operator new never returns NULL; it will instead throw a std::bad_alloc exception if it cannot allocate memory.

#include <cstring>
 
void
int f(const int * array, std::size_t size) noexcept(false) {
  int * copy;
  try {
    copy = new int[size];
  }
  catch (std::bad_alloc&) {
    // Indicate error to caller.
    return -1;
  }

  std::memcpy(copy, array, size * sizeof *copy);
  // ...
  delete[] copy;

  // Indicate successful completion.
  return 0;
}
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.

struct A { /* ... */ };
struct B { /* ... */ }; 
 
void g(A *, B *);
void f() {
  g(new A, new B);
}

Consider the situation 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.

#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.

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.

Wiki MarkupIf 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 \[ [VU#159523|http://www.kb.cert.org/vuls/id/159523]\].

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	Include Page Helix QAC_V Helix QAC_V	C++3225, C++3226, C++3227, C++3228, C++3229, C++4632
Klocwork	Include Page Klocwork_V Klocwork_V	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	Include Page LDRA_V LDRA_V	45 D	Partially implemented
Parasoft C/C++test	Include Page Parasoft_V Parasoft_V	CERT_CPP-MEM52-a CERT_CPP-MEM52-b	Check the return value of new Do not allocate resources in function argument list because the order of evaluation of a function's parameters is undefined
Parasoft Insure++			Runtime detection
Polyspace Bug Finder	Include Page Polyspace Bug Finder_V Polyspace Bug Finder_V	CERT C++: MEM52-CPP	Checks for unprotected dynamic memory allocation (rule partially covered)
PVS-Studio	Include Page PVS-Studio_V PVS-Studio_V	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, 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

Fortify SCA Version 5.0 can detect violations of this rule.

Compass/ROSE can detect violations of this rule. In particular, it ensures that variables are compared to NULL before being used, as in EXP34-CPP. Ensure a null pointer is not dereferenced.

Related Vulnerabilities

Wiki MarkupThe vulnerability in Adobe Flash \[[VU#159523|AA. References#VU#159523]\] 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, but rather 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 the CERT website.

Other Languages

...

Related Guidelines

...

...

References

...

Bibliography

...

...

...

...

...

Image Added Image Added Image Added2003|AA. References#ISO/IEC 14882-2003]\] Section 5.3.4 \[[Meyers 95|AA. References#Meyers 95]\] Item 7. Be prepared for out-of-memory conditions. \[[MITRE|AA. References#MITRE]\] [CWE ID 252|http://cwe.mitre.org/data/definitions/252.html], "Unchecked Return Value" \[MITRE\] [CWE ID 391|http://cwe.mitre.org/data/definitions/391.html], "Unchecked Error Condition" \[MITRE\] [CWE ID 476|http://cwe.mitre.org/data/definitions/476.html], "NULL Pointer Dereference" \[MITRE\] [CWE ID 690|http://cwe.mitre.org/data/definitions/690.html], "Unchecked Return Value to NULL Pointer Dereference" \[MITRE\] [CWE ID 703|http://cwe.mitre.org/data/definitions/703.html], "Failure to Handle Exceptional Conditions" \[MITRE\] [CWE ID 754|http://cwe.mitre.org/data/definitions/754.html], "Improper Check for Unusual or Exceptional Conditions" \[[Seacord 05|AA. References#Seacord 05]\] Chapter 4, "Dynamic Memory Management" \[[VU#159523|AA. References#VU#159523]\]MEM31-CPP. Free dynamically allocated memory exactly once      08. Memory Management (MEM)      MEM34-CPP. Only free memory allocated dynamically