src/alarmwrite.c

   1 #include <stdlib.h>
   2 #include <stdio.h>
   3 #include <dlfcn.h>
   4 #include <unistd.h>
   5
   6 ssize_t write(int fd, const void *buf, size_t count)
   7 {
   8         int (*real_write)(int fd, const void *buf, size_t count) = NULL;
   9         int real_write_return;
  10         int alarm_sec = 2;
  11
  12         if (real_write == NULL) {
  13                 void *handle = dlopen(/* "/lib/libc.so.6" */ "/lib/i386-linux-gnu/libc.so.6", RTLD_LAZY);
  14                 if (handle == NULL) {
  15                         fprintf(stderr, "dlopen: %s\n", dlerror());
  16                         exit(1);
  17                 }
  18                 real_write = dlsym(handle, "write");
  19                 if (real_write == NULL) {
  20                         fprintf(stderr, "dlsym: %s\n", dlerror());
  21                         exit(1);
  22                 }
  23         }
  24
  25         alarm(alarm_sec);
  26         real_write_return = real_write(fd, buf, count);
  27         alarm(0);
  28         return real_write_return;
  29 }
  30
  31 // Fordítás: gcc -s -x c alarmwrite.c -fPIC -shared -o alarmwrite.so
  32 // Futtatás: LD_PRELOAD=./alarmwrite.so x2vnc host:display