CWE Rule 705

This issue occurs when an exit handler itself calls another function that interrupts the program’s expected termination sequence and causes an abnormal exit.

If your exit handler terminates your program, you can have undefined behavior. Abnormal program termination means other exit handlers are not invoked. These additional exit handlers may do additional clean up or other required termination steps.

In inside exit handlers, remove calls to functions that prevent the exit handler from terminating normally.

#include <stdlib.h>

volatile int some_condition = 1;
void demo_exit1(void)
{
    /* ... Cleanup code ... */
    return;
}
void exitabnormalhandler(void)
{
    if (some_condition)
    {
        /* Clean up */
        exit(0); //Noncompliant
    }
    return;
}

int demo_install_exitabnormalhandler(void)
{

    if (atexit(demo_exit1) != 0) /* demo_exit1() performs additional cleanup */
    {
        /* Handle error */
    }
    if (atexit(exitabnormalhandler) != 0)
    {
        /* Handle error */
    }
    /* ... Program code ... */
    return 0;
}

In this example, demo_install_exitabnormalhandler registers two exit handlers, demo_exit1 and exitabnormalhandler. Exit handlers are invoked in the reverse order of which they are registered. When the program ends, exitabnormalhandler runs, then demo_exit1. However, exitabnormalhandler calls exit interrupting the program exit process. Having this exit inside an exit handler causes undefined behavior because the program is not finished cleaning up safely.

One possible correction is to let your exit handlers terminate normally. For this example, exit is removed from exitabnormalhandler, allowing the exit termination process to complete as expected.

#include <stdlib.h>

volatile int some_condition = 1;
void demo_exit1(void)
{
    /* ... Cleanup code ... */
    return;
}
void exitabnormalhandler(void)
{
    if (some_condition)
    {
        /* Clean up */
        /* Return normally */
    }
    return;
}

int demo_install_exitabnormalhandler(void)
{

    if (atexit(demo_exit1) != 0) /* demo_exit1() continues clean up */
    {
        /* Handle error */
    }
    if (atexit(exitabnormalhandler) != 0) 
    {
        /* Handle error */
    }
    /* ... Program code ... */
    return 0;
}