How to override connect() system call called from within PHP script, in an Apache request, when PHP is enabled via mod_php?
I have my custom connect() version defined in custom-connect.c:
#define _GNU_SOURCE 1
#include <stdio.h>
#include <arpa/inet.h>
#include <dlfcn.h>
int (*real_connect)(int, const struct sockaddr *, socklen_t);
FILE *f;
void _init (void) {
const char *err;
f = fopen("/tmp/connect.log", "a");
real_connect = dlsym (RTLD_NEXT, "connect");
if ((err = dlerror()) != NULL) {
fprintf (f, "dlsym (connect): %s
", err);
}
}
int connect(int fd, const struct sockaddr *sk, socklen_t sl) {
static struct sockaddr_in *sk_in;
sk_in = (struct sockaddr_in *)sk;
fprintf(f, "Custom connect: %d %s:%d
", fd, inet_ntoa(sk_in->sin_addr), ntohs(sk_in->sin_port));
return real_connect(fd, sk, sl);
}
I compile it with:
gcc -nostartfiles -fpic -shared custom-connect.c -o custom-connect.so -ldl
I have a simple script curl-test.php, that internally makes calls to the connect():
<?php
$ch = curl_init("http://example.com");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$data = curl_exec($ch);
curl_close($ch);
echo 'Received length: ' . strlen($data) . "
";
When I run my script with LD_PRELOAD from command line:
LD_PRELOAD=./custom-connect.so php curl-test.php
Then it looks fine, i can see that my custom connect() logged something to /tmp/connect.log:
Custom connect: 4 192.168.178.1:53
Custom connect: 4 93.184.216.34:80
It looks like it works fine from the command line. But how can I override connect() with my own version, when I run my script from Apache with PHP enabled via mod_php? Should I also use LD_PRELOAD? If yes, then how to configure it?
