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Subject: Re: source IP address
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Thread-Topic: source IP address
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From: "Robert S. Wojciechowski Jr." <robertw@wojo.com>
To: <freebsd-stable@FreeBSD.ORG>, <freebsd-questions@FreeBSD.ORG>
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Has anyone tried using LD_PRELOAD to force a program to bind to a =
specific
IP? =20

For instance you could start ssh like so:

$ LD_PRELOAD=3D<dir>/preload.so
$ export LD_PRELOAD
$ <run the program>
$ unset LD_PRELOAD

Or making a wrapper program would be nice,

$ bindto <ip> <program ...>

Here is some code I found, but I haven't had the time or been able to =
get it
to work in FreeBSD.  Can anyone get this to work?

gcc -c -fPIC preload.c
ld -o preload.so -G preload.o


#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <dlfcn.h>

#define LIBRARY "/usr/lib/libsocket.so"
#define ADDRESS "YOUR IP ADDRESS GOES HERE"
#define TRUE 1
#define FALSE 0

int bind (int s, struct sockaddr *name, int namelen)
{
    void *Handle;
    int (*Fptr)(int, struct sockaddr *, int);
    int Found =3D FALSE;
   =20
    /* Look for inet type sockets */

    if (name->sa_family =3D=3D AF_INET) {
        Found =3D TRUE;
    }

    /* Open the library */

    Handle =3D dlopen (LIBRARY, RTLD_LAZY);

    /* Get the function symbol out of the library */

    Fptr =3D (int (*)(int, struct sockaddr *, int)) dlsym (Handle, =
"bind");

    /*
     * If this is an inet socket, make it find to the local ip and not
     * all ips on the box
     */
=20
    if (Found) {
        if (((struct sockaddr_in *) name)->sin_addr.s_addr =3D=3D
            htonl (INADDR_ANY)) {
            ((struct sockaddr_in *) name)->sin_addr.s_addr =3D
                inet_addr (ADDRESS);
        }
=20
        /* Call the real function with the new struct */
=20
        (*Fptr)(s, name, namelen);
    }
    else {
=20
        /* Call the real function with the original struct */
=20
        (*Fptr)(s, name, namelen);
    }
=20
    /* Cleanup and close the library */
=20
    dlclose (Handle);
}



---
Robert S. Wojciechowski Jr.
robertw@wojo.com

-----------------------------------------------------------------
> On 14-Nov-2000 13:42:01, Matt Dillon writes:
>=20
> :
> :On Mon, Nov 13, 2000 at 06:59:13PM -0800, Matt Dillon wrote:
> :>=20
> :>     Some programs, such as ping and traceroute, allow you to bind
> :>     to a specific source IP address.  Most programs don't, though.
> :>=20
> :> 						-Matt
> :
> :Telnet does.  It would be really used if ssh did also.
> :
> :Joe
> :--=20
> :Josef Karthauser	FreeBSD: How many times have you booted today?
> :Technical Manager	Viagra for your server (http://www.uk.freebsd.org)
> :Pavilion Internet plc.  [joe@pavilion.net, joe@uk.freebsd.org,
joe@tao.org.uk]
>=20
>     Yah, it would be really nice if ssh did too... I have a box with
>     five IP addresses on it, some externally routed, some NAT'd, some
>     internal, and ssh'ing out from it without being able to bind to a
>     specific IP makes setting up security difficult.
>=20
>     It's utterly trivial to add, but I don't have time myself.
>=20
>     It is possible to use a jail to force the source IP address, but
>     jail's do not appear to work well with interactive tty's.  ssh =
gets
>     really confused when run from a jail.
>=20
> 						-Matt
>=20
>=20
>=20
> To Unsubscribe: send mail to majordomo@FreeBSD.org
> with "unsubscribe freebsd-stable" in the body of the message
>=20
>=20



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