Operation on Resource in Wrong Phase of Lifetime

Description

A resource's lifecycle includes several phases: initialization, use, and release. For each phase, it is important to follow the specifications outlined for how to operate on the resource and to ensure that the resource is in the expected phase. Otherwise, if a resource is in one phase but the operation is not valid for that phase (i.e., an incorrect phase of the resource's lifetime), then this can produce resultant weaknesses. For example, using a resource before it has been fully initialized could cause corruption or incorrect data to be used.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following code shows a simple example of a double free vulnerability.

char* ptr = (char*)malloc (SIZE);
...
if (abrt) {
  free(ptr);
}
...
free(ptr);

Double free vulnerabilities have two common (and sometimes overlapping) causes:

Although some double free vulnerabilities are not much more complicated than this example, most are spread out across hundreds of lines of code or even different files. Programmers seem particularly susceptible to freeing global variables more than once.

See Also