/etc/ld.so.preload

[Milan Pikula - WWW]

On Mon, 13 Sep 1999, Marek Antozi wrote:

W>Chcel by som sa opýtať, ako sa používa %subject%, prípadne postačí aj
W>použitie pomocu nastavenia premennej prostredia.

1. spravi sa library, ktora definuje niektore symboly, ktore chceme
prekryt v originali.
2. cez LD_PRELOAD v enve alebo cez zmieneny subor sa povie dynamickemu
linkeru, ze sa ma pouzit.

Prave dnes som niekomu naprogramoval tento priklad:

www na fornax[78, 578]: ~$ cat test.c
#include <stdio.h>
#include <dlfcn.h>

#include <sys/types.h>
#include <sys/socket.h>

/*
 NOTE from my man page:
 The third argument of connect is in reality  an  int  (and this  is  what BSD
 4.*  and libc4 and libc5 have).  Some POSIX confusion resulted in the present
 socklen_t.   The draft  standard  has  not  been  adopted  yet,  but glibc2
 already follows  it  and  also  has  socklen_t.  See  also accept(2).
 */
#define socklen_t int

static int (*real_connect)(int, const struct sockaddr *, socklen_t);

void _init()
{
        real_connect = (int (*)(int, const struct sockaddr *, socklen_t))
                (dlsym(RTLD_NEXT, "connect"));
}

void _fini()
{
}

int connect(int i1, const struct sockaddr * p1, socklen_t i2)
{
        puts("connect ;)");
        return real_connect(i1, p1, i2);
}
www na fornax[79, 579]: ~$ gcc -Wall -nostdlib -shared -o test.so test.c -ldl
www na fornax[85, 585]: ~$ LD_PRELOAD=./test.so telnet 0 2345
Trying 0.0.0.0...
connect
telnet: Unable to connect to remote host: Connection refused
www na fornax[86, 586]: ~$

	Milan Pikula

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