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@stefansundin /bind.c
Last active Aug 29, 2015

Bind programs to specific network interface. (Linux)
/*
https://gist.github.com/stefansundin/e4fce00d97f7694c7a27
http://www.ryde.net/code/bind.c.txt
http://daniel-lange.com/archives/53-Binding-applications-to-a-specific-IP.html
*/
/*
Copyright (C) 2000 Daniel Ryde
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
*/
/*
LD_PRELOAD library to make bind and connect to use a virtual
IP address as localaddress. Specified via the enviroment
variable BIND_ADDR.
Compile on Linux with:
gcc -nostartfiles -fpic -shared bind.c -o bind.so -ldl -D_GNU_SOURCE
Example in bash to make inetd only listen to the localhost
lo interface, thus disabling remote connections and only
enable to/from localhost:
BIND_ADDR="127.0.0.1" LD_PRELOAD=./bind.so /sbin/inetd
Example in bash to use your virtual IP as your outgoing
sourceaddress for ircII:
BIND_ADDR="your-virt-ip" LD_PRELOAD=./bind.so ircII
Note that you have to set up your servers virtual IP first.
This program was made by Daniel Ryde
email: daniel@ryde.net
web: http://www.ryde.net/
TODO: I would like to extend it to the accept calls too, like a
general tcp-wrapper. Also like an junkbuster for web-banners.
For libc5 you need to replace socklen_t with int.
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <dlfcn.h>
#include <errno.h>
int (*real_bind)(int, const struct sockaddr *, socklen_t);
int (*real_connect)(int, const struct sockaddr *, socklen_t);
char *bind_addr_env;
unsigned long int bind_addr_saddr;
unsigned long int inaddr_any_saddr;
struct sockaddr_in local_sockaddr_in[] = { 0 };
void _init (void)
{
const char *err;
real_bind = dlsym (RTLD_NEXT, "bind");
if ((err = dlerror ()) != NULL) {
fprintf (stderr, "dlsym (bind): %s\n", err);
}
real_connect = dlsym (RTLD_NEXT, "connect");
if ((err = dlerror ()) != NULL) {
fprintf (stderr, "dlsym (connect): %s\n", err);
}
inaddr_any_saddr = htonl (INADDR_ANY);
if ((bind_addr_env = getenv ("BIND_ADDR"))) {
bind_addr_saddr = inet_addr (bind_addr_env);
local_sockaddr_in->sin_family = AF_INET;
local_sockaddr_in->sin_addr.s_addr = bind_addr_saddr;
local_sockaddr_in->sin_port = htons (0);
}
}
int bind (int fd, const struct sockaddr *sk, socklen_t sl)
{
static struct sockaddr_in *lsk_in;
lsk_in = (struct sockaddr_in *)sk;
// printf("bind: %d %s:%d\n", fd, inet_ntoa (lsk_in->sin_addr.s_addr), ntohs (lsk_in->sin_port));
if ((lsk_in->sin_family == AF_INET)
&& (lsk_in->sin_addr.s_addr == inaddr_any_saddr)
&& (bind_addr_env)) {
lsk_in->sin_addr.s_addr = bind_addr_saddr;
}
return real_bind (fd, sk, sl);
}
int connect (int fd, const struct sockaddr *sk, socklen_t sl)
{
static struct sockaddr_in *rsk_in;
rsk_in = (struct sockaddr_in *)sk;
// printf("connect: %d %s:%d\n", fd, inet_ntoa (rsk_in->sin_addr.s_addr), ntohs (rsk_in->sin_port));
if ((rsk_in->sin_family == AF_INET)
&& (bind_addr_env)) {
real_bind (fd, (struct sockaddr *)local_sockaddr_in, sizeof (struct sockaddr));
}
return real_connect (fd, sk, sl);
}
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