CERT.MEM.PLACEMENTNEW.TOOSMALL
Provide placement new with sufficient storage.
Vulnerability and risk
Passing improperly aligned pointers or pointers to insufficient storage to placement new expressions can result in undefined behavior, including buffer overflow and abnormal termination.
Mitigation and prevention
Do not pass a pointer that is not suitably aligned for the object being constructed to placement new. Doing so results in an object being constructed at a misaligned location, which results in undefined behavior. Do not pass a pointer that has insufficient storage capacity for the object being constructed, including the overhead required for arrays. Doing so may result in initialization of memory outside of the bounds of the object being constructed, which results in undefined behavior.
Finally, do not use placement new[] on any platform that does not specify a limit for the overhead it requires.
Noncompliant code example
#include <new>
void f() {
short s;
long *lp = ::new (&s) long;
}In this noncompliant code example, a pointer to a short is passed to placement new, which is attempting to initialize a long. On architectures where sizeof(short) < sizeof(long), this results in undefined behavior. This example, and subsequent ones, all assume the pointer returned by placement new will not be used after the lifetime of its underlying storage has ended. For instance, the pointer will not be stored in a static global variable and dereferenced after the call to f() has ended. This assumption is in conformance with MEM50-CPP. Do not access freed memory.
Compliant solution
#include <new>
void f() {
char c; // Used elsewhere in the function
alignas(long) unsigned char buffer[sizeof(long)];
long *lp = ::new (buffer) long;
// ...
}In this compliant solution, the alignas declaration specifier is used to ensure the buffer is appropriately aligned for a long.