95 lines
2.8 KiB
C
95 lines
2.8 KiB
C
/*
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* rebind: Intercept bind calls and bind to a different port
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* Copyright 2010 Joel Martin
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* Licensed under LGPL version 3 (see docs/LICENSE.LGPL-3)
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*
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* Overload (LD_PRELOAD) bind system call. If REBIND_PORT_OLD and
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* REBIND_PORT_NEW environment variables are set then bind on the new
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* port (of localhost) instead of the old port.
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*
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* This allows a bridge/proxy (such as websockify) to run on the old port and
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* translate traffic to/from the new port.
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*
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* Usage:
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* LD_PRELOAD=./rebind.so \
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* REBIND_PORT_OLD=23 \
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* REBIND_PORT_NEW=2023 \
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* program
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*/
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//#define DO_DEBUG 1
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#include <stdio.h>
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#include <stdlib.h>
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#define __USE_GNU 1 // Pull in RTLD_NEXT
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#include <dlfcn.h>
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#include <string.h>
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#include <netinet/in.h>
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#if defined(DO_DEBUG)
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#define DEBUG(...) \
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fprintf(stderr, "rebind: "); \
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fprintf(stderr, __VA_ARGS__);
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#else
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#define DEBUG(...)
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#endif
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int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
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{
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static void * (*func)();
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int do_move = 0;
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struct sockaddr_in * addr_in = (struct sockaddr_in *)addr;
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struct sockaddr_in addr_tmp;
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socklen_t addrlen_tmp;
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char * PORT_OLD, * PORT_NEW, * end1, * end2;
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int ret, oldport, newport, askport = htons(addr_in->sin_port);
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uint32_t askaddr = htons(addr_in->sin_addr.s_addr);
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if (!func) func = (void *(*)()) dlsym(RTLD_NEXT, "bind");
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DEBUG(">> bind(%d, _, %d), askaddr %d, askport %d\n",
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sockfd, addrlen, askaddr, askport);
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/* Determine if we should move this socket */
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if (addr_in->sin_family == AF_INET) {
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// TODO: support IPv6
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PORT_OLD = getenv("REBIND_OLD_PORT");
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PORT_NEW = getenv("REBIND_NEW_PORT");
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if (PORT_OLD && (*PORT_OLD != '\0') &&
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PORT_NEW && (*PORT_NEW != '\0')) {
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oldport = strtol(PORT_OLD, &end1, 10);
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newport = strtol(PORT_NEW, &end2, 10);
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if (oldport && (*end1 == '\0') &&
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newport && (*end2 == '\0') &&
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(oldport == askport)) {
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do_move = 1;
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}
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}
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}
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if (! do_move) {
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/* Just pass everything right through to the real bind */
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ret = (long) func(sockfd, addr, addrlen);
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DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
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return ret;
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}
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DEBUG("binding fd %d on localhost:%d instead of 0x%x:%d\n",
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sockfd, newport, ntohl(addr_in->sin_addr.s_addr), oldport);
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/* Use a temporary location for the new address information */
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addrlen_tmp = sizeof(addr_tmp);
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memcpy(&addr_tmp, addr, addrlen_tmp);
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/* Bind to other port on the loopback instead */
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addr_tmp.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
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addr_tmp.sin_port = htons(newport);
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ret = (long) func(sockfd, &addr_tmp, addrlen_tmp);
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DEBUG("<< bind(%d, _, %d) ret %d\n", sockfd, addrlen, ret);
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return ret;
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}
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