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A signal handler should not reassert its desire to handle its own signal. This is often done on nonpersistent platforms; that is, platforms that, upon receiving a signal, reset the disposition for the signal to default before calling the bound signal handler. See recommendation SIG01-C. Understand implementation-specific details regarding signal handler persistence.

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void handler(int signum) {
  if (signal(signum, handler) == SIG_ERR) {
    /* Handle error */
  }
  /* Handle signal */
}
/* ... */
if (signal(SIGUSR1, handler) == SIG_ERR) {
  /* Handle error */
}

...

void handler(int signum) {
  /* Handle signal */
}
/* ... */
if (signal(SIGUSR1, handler) == SIG_ERR) {
  /* Handle error */
}

...

void handler(int signum) {
  /* Handle signal */
}

/* ... */

struct sigaction act;
act.sa_handler = handler;
act.sa_flags = 0;
if (sigemptyset( &act.sa_mask) != 0) {
  /* Handle error */
}
if (sigaction(SIGUSR1, &act, NULL) != 0) {
  /* Handle error */
}

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POSIX recommends sigaction() and deprecates signal(). Unfortunately, sigaction() is not C99C-compliant and is not supported on some platforms, including Windows.

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SIG34-EX1: On a machine with persistent signal handlers, it is safe for a handler to modify the behavior for its own signal. This would include having the signal be ignored, reset to default behavior, or handled by a different handler. A handler assigning itself to its own signal is also safe, as it is a no-op. Since multiple invocations of its signal will merely cause it to "interrupt itself," , the handler is impervious to a race condition until it manages to reassign its signal.

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void handler(int signum) {
#ifndef WINDOWS
  if (signal(signum, SIG_DFL) == SIG_ERR) {
    /* Handle error */
  }
#endif
  /* Handle signal */
}
/* ... */
if (signal(SIGUSR1, handler) == SIG_ERR) {
  /* Handle error */
}

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Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

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ISO/IEC 9899-1999TR2 Section 7.14.1.1, "The signal function"

ISO/IEC TR 17961 (Draft) Calling signal from interruptible signal handlers [sigcall]

MITRE CWE: CWE-479, "Unsafe Function Call from a Signal Handler"

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