CWE Rule 432

This issue occurs if the handler of a signal can be reentered by the same signal during its execution. Polyspace^® reports a violation if the signal handler performs any action without performing one of these actions first:

If the signal handler does not stop listening for the current signal, the handler can be reentered if the current signal is received again during the execution of the handler. Consider this signal handler:

#include <signal.h>
int shared_state = 0;

void signal_handler(int signum) {
	shared_state++;
}

int main() {
	//...
	signal(SIGINT, signal_handler);
	signal(SIGTERM, signal_handler);
}

In the signal handler function, before performing any action, set the handling of the current signal to the default action. Alternatively, ignore the current signal during the signal handling operations. Finally, before exiting the signal handler, assign the current handler to the current signal again. The signal_handler function in the preceding code can be fixed as follows:

void signal_handler(int signum) {
	signal(signum, SIG_DFL);
	shared_state++;
	signal(signum, signal_handler);
}

In this example, the handlers increment_handler() and decrement_handler() can be interrupted during their execution. Polyspace reports violations.

#include <stdio.h>
#include <signal.h>


volatile sig_atomic_t counter = 0;

void increment_handler(int signum) {  //Noncompliant
	counter++;
}

void decrement_handler(int signum) { //Noncompliant
	counter--;
}

int main() {
	signal(SIGUSR1, increment_handler);
	signal(SIGUSR2, decrement_handler);
	//...
	return 0;
}

To fix these violations, disable the handlers first before performing any action in the handlers.

#include <stdio.h>
#include <signal.h>


volatile sig_atomic_t counter = 0;

void increment_handler(int signum) {  //Compliant
	signal(signum, SIG_DFL);
	counter++;
	signal(signum, increment_handler);
}

void decrement_handler(int signum) { //Compliant
	signal(signum, SIG_DFL);
	counter--;
	signal(signum, increment_handler);
}

int main() {
	signal(SIGUSR1, increment_handler);
	signal(SIGUSR2, decrement_handler);
	//...
	return 0;
}