src/forcebindip.c

   1 /**
   2  * forcebindip.c
   3  *
   4  * Compile with: gcc -D _GNU_SOURCE -shared -fPIC -o forcebindip.so forcebindip.c
   5  *
   6  * Usage: LD_PRELOAD=./forcebindip.so BIND_ADDRESS=1.2.3.4 wget ...
   7  */
   8
   9 #include <stdio.h>
  10 #include <stdlib.h>
  11 #include <sys/types.h>
  12 #include <sys/socket.h>
  13 #include <netinet/in.h>
  14 #include <arpa/inet.h>
  15 #include <dlfcn.h>
  16 #include <errno.h>
  17 #include <err.h>
  18
  19 int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
  20 {
  21         char *ip;
  22         struct in_addr inaddr;
  23         struct sockaddr_in sin;
  24
  25         ip = getenv("BIND_ADDRESS");
  26
  27         if (ip != NULL)
  28         {
  29                 if(inet_aton(ip, &inaddr) == 0)
  30                 {
  31                         warnx("forcebindip: Invalid address: %s", ip);
  32                 }
  33                 else
  34                 {
  35                         sin.sin_family = AF_INET;
  36                         sin.sin_port = 0;
  37                         sin.sin_addr = inaddr;
  38
  39                         if(bind(sockfd, (struct sockaddr *)&sin, sizeof(sin)) < 0)
  40                         {
  41                                 warn("forcebindip: bind: %s", ip);
  42                         }
  43                 }
  44         }
  45
  46         int (*orig_connect)(int, const struct sockaddr *, socklen_t) = dlsym(RTLD_NEXT, "connect");
  47         return orig_connect(sockfd, addr, addrlen);
  48 }
  49