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Non-Compliant Coding Example

Using the longjmp function inside a signal handler is particularly dangerous, as it could call any part of your code.

#include <setjmp.h> 
#include <signal.h> 
 
static jmp_buf env; 
 
void int_handler() { 
  longjmp(env, 1); 
} 
 
int main() { 
  char *foo; 

  signal(SIGINT, int_handler); 
 
  if(setjmp(env) == 0) { 
    foo = malloc(15);
    foo = "Nothing yet.";
  }
  else {
    foo = "Signal caught.";
  }

  /* main loop which displays foo */

  return 0;
}

Compliant Solution

Signal handlers should be as minimal as possible, only unconditionally setting a flag where appropriate, and returning.

#include <setjmp.h> 
#include <signal.h> 
 
static jmp_buf env; 
int interrupted = 0;
 
void int_handler() { 
  interrupted = 1;
} 
 
int main() { 
  char *foo; 

  signal(SIGINT, int_handler); 
    
  foo = malloc(15);
  foo = "Nothing yet.";
  
  /* main loop which displays foo */
  if(interrupt == 1) {
    foo = "Signal caught.";
  }

  return 0;
}

Risk Assessment

Depending on the code, this could lead to any number of attacks, many of which could give root access. This is extremely dangerous. For an overview of actual issuessome software vulnerabilities, see Zalewski's signal article.

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