2011年8月8日 星期一

處理 Stack Overflow

直接看程式碼比較快:

#define _XOPEN_SOURCE 600

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

sigjmp_buf stack_overflow_guard;

char alter_stack[4096];

void sigsegv_handler(int sig) {
  if (sig == SIGSEGV) {
    /* Jump to catch block */
    siglongjmp(stack_overflow_guard, sig);
  }
}

void install_sigsegv_handler() {
  /* Prepare alternating stack */
  stack_t stk;

  stk.ss_sp = alter_stack;
  stk.ss_size = sizeof(alter_stack);
  stk.ss_flags = 0;

  if (sigaltstack(&stk, NULL) == -1) {
    fprintf(stderr, "ERROR: Unable to setup alternative stack.\n");
    exit(EXIT_FAILURE);
  }

  /* Register SIGSEGV handler */
  struct sigaction act;

  act.sa_handler = &sigsegv_handler;
  sigfillset(&act.sa_mask);
  act.sa_flags |= SA_ONSTACK;

  if (sigaction(SIGSEGV, &act, NULL) == -1) {
    fprintf(stderr, "ERROR: Unable to instal signal handler.\n");
    exit(EXIT_FAILURE);
  }
}

int trigger_stack_overflow(int a, int b, int c, int d, int e) {
  return trigger_stack_overflow(a + 1, b + 1, c + 1, d + 1, e + 1) *
         trigger_stack_overflow(a - 1, b - 1, c - 1, d - 1, e - 1);
}

int main() {
  install_sigsegv_handler();

  if (sigsetjmp(stack_overflow_guard, 0) == 0) {
    printf("normal path, got: %d\n",
           trigger_stack_overflow(0, 0, 0, 0, 0));
  } else {
    printf("stack overflow\n");
  }

  return EXIT_SUCCESS;
}

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