utils/rebind.c

   1 /*
   2  * rebind: Intercept bind calls and bind to a different port
   3  * Copyright 2010 Joel Martin
   4  * Licensed under MPL-2.0 (see docs/LICENSE.MPL-2.0)
   5  *
   6  * Overload (LD_PRELOAD) bind system call. If REBIND_PORT_OLD and
   7  * REBIND_PORT_NEW environment variables are set then bind on the new
   8  * port (of localhost) instead of the old port.
   9  *
  10  * This allows a proxy (such as wsproxy) to run on the old port and translate
  11  * traffic to/from the new port.
  12  *
  13  * Usage:
  14  *     LD_PRELOAD=./rebind.so \
  15  *     REBIND_PORT_OLD=23 \
  16  *     REBIND_PORT_NEW=2023 \
  17  *     program
  18  */
  19
  20 //#define DO_DEBUG 1
  21
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24
  25 #define __USE_GNU 1  // Pull in RTLD_NEXT
  26 #include <dlfcn.h>
  27
  28 #include <string.h>
  29 #include <netinet/in.h>
  30
  31
  32 #if defined(DO_DEBUG)
  33 #define DEBUG(...) \
  34     fprintf(stderr, "wswrapper: "); \
  35     fprintf(stderr, __VA_ARGS__);
  36 #else
  37 #define DEBUG(...)
  38 #endif
  39
  40
  41 int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
  42 {
  43     static void * (*func)();
  44     int do_move = 0;
  45     struct sockaddr_in * addr_in = (struct sockaddr_in *)addr;
  46     struct sockaddr_in addr_tmp;
  47     socklen_t addrlen_tmp;
  48     char * PORT_OLD, * PORT_NEW, * end1, * end2;
  49     int ret, oldport, newport, askport = htons(addr_in->sin_port);
  50     uint32_t askaddr = htons(addr_in->sin_addr.s_addr);
  51     if (!func) func = (void *(*)()) dlsym(RTLD_NEXT, "bind");
  52
  53     DEBUG(">> bind(%d, _, %d), askaddr %d, askport %d\n",
  54           sockfd, addrlen, askaddr, askport);
  55
  56     /* Determine if we should move this socket */
  57     if (addr_in->sin_family == AF_INET) {
  58         // TODO: support IPv6
  59         PORT_OLD = getenv("REBIND_OLD_PORT");
  60         PORT_NEW = getenv("REBIND_NEW_PORT");
  61         if (PORT_OLD && (*PORT_OLD != '\0') &&
  62             PORT_NEW && (*PORT_NEW != '\0')) {
  63             oldport = strtol(PORT_OLD, &end1, 10);
  64             newport = strtol(PORT_NEW, &end2, 10);
  65             if (oldport && (*end1 == '\0') &&
  66                 newport && (*end2 == '\0') &&
  67                 (oldport == askport)) {
  68                 do_move = 1;
  69             }
  70         }
  71     }
  72
  73     if (! do_move) {
  74         /* Just pass everything right through to the real bind */
  75         ret = (int) func(sockfd, addr, addrlen);
  76         DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
  77         return ret;
  78     }
  79
  80     DEBUG("binding fd %d on localhost:%d instead of 0x%x:%d\n",
  81         sockfd, newport, ntohl(addr_in->sin_addr.s_addr), oldport);
  82
  83     /* Use a temporary location for the new address information */
  84     addrlen_tmp = sizeof(addr_tmp);
  85     memcpy(&addr_tmp, addr, addrlen_tmp);
  86
  87     /* Bind to other port on the loopback instead */
  88     addr_tmp.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
  89     addr_tmp.sin_port = htons(newport);
  90     ret = (int) func(sockfd, &addr_tmp, addrlen_tmp);
  91
  92     DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
  93     return ret;
  94 }