src/cupspwd.c

   1 #define _GNU_SOURCE
   2 #include <stdlib.h>
   3 #include <stdio.h>
   4 #include <unistd.h>
   5 #include <dlfcn.h>
   6 #include <string.h>
   7 #include <err.h>
   8 #include <errno.h>
   9 #include <sys/types.h>
  10 #include <sys/stat.h>
  11
  12 //typedef ssize_t (*_read_f_t_)(int fd, void *buf, size_t count);
  13 //static _read_f_t_ _read_f_ = NULL;
  14
  15 ssize_t read(int fd, void *buf, size_t count)
  16 {
  17         int (*real_read)(int fd, void *buf, size_t count) = NULL;
  18         char fdpath[21];
  19         char *pwd;
  20         struct stat st;
  21
  22         warnx("intercepted fd=%d", fd);
  23
  24 /*
  25         _read_f_ = (_read_f_t_)dlsym(RTLD_NEXT, "read");
  26         warnx("-> %p", _read_f_);
  27         if (_read_f_ == NULL)
  28                         errx(1, "dlsym: %s", dlerror());
  29 */
  30         if(real_read == NULL)
  31         {
  32                 void *handle = dlopen("/lib/i386-linux-gnu/libc.so.6", RTLD_LAZY);
  33                 if (handle == NULL)
  34                         errx(1, "dlopen: %s", dlerror());
  35                 real_read = dlsym(handle, "read");
  36                 if (real_read == NULL)
  37                         errx(1, "dlopen: %s", dlerror());
  38         }
  39
  40         snprintf(fdpath, 21, "/proc/self/fd/%d", fd);
  41         if(lstat(fdpath, &st) == 0)
  42         {
  43                 if(major(st.st_rdev) == 5 && minor(st.st_rdev) == 0)
  44                 {
  45                         pwd = getenv("CUPS_PASSWORD");
  46                         if(pwd != NULL)
  47                         {
  48                                 if(count >= strlen(pwd))
  49                                 {
  50                                         sprintf(buf, "%s\n", pwd);
  51                                         return strlen(pwd)+1;
  52                                 }
  53                                 else
  54                                 {
  55                                         warnx("Buffer is too small, %d, %d.", count, stren(pwd));
  56                                 }
  57                         }
  58                         else
  59                         {
  60                                 warnx("CUPS_PASSWORD is not set.");
  61                         }
  62                 }
  63         }
  64         else
  65         {
  66                 warn("lstat: %s", fdpath);
  67         }
  68         return real_read(fd, buf, count);
  69 //      return _read_f_(fd, buf, count);
  70 }
  71
  72 // Fordítás: gcc -s -x c cupspwd.c -fPIC -shared -o cupspwd.so
  73 // Futtatás: CUPS_PASSWORD=xxx LD_PRELOAD=./cupspwd.so lpstat -l -t