Description:
------------
When using system() (or other functions) to execute a program, the child process inherits the FPM's file descriptors, which led to some security issues such as hijacking some requests to the FPM using the leaked socket file descriptor.

Test script:
---------------
<?php
system("sleep 60");    // and go check the sleep process's fd

Expected result:
----------------
[root@localhost html]# ls -al /proc/20928/fd       // php-fpm's FDs
total 0
dr-x------ 2 root root  0 Aug 27 22:46 .
dr-xr-xr-x 9   82   82  0 Aug 27 22:46 ..
lrwx------ 1 root root 64 Aug 27 22:46 0 -> /dev/null
l-wx------ 1 root root 64 Aug 27 22:46 1 -> pipe:[372386]
l-wx------ 1 root root 64 Aug 27 22:46 2 -> pipe:[372387]
l-wx------ 1 root root 64 Aug 27 22:46 4 -> /dev/pts/0
lrwx------ 1 root root 64 Aug 27 22:46 9 -> socket:[372385]
// FPM process containing socket and other sensitive FDs

[root@localhost html]# ls -al /proc/ChildPID/fd     // child process's FDs
total 0
dr-x------ 2 root root  0 Aug 27 22:46 .
dr-xr-xr-x 9   82   82  0 Aug 27 22:46 ..
lrwx------ 1 root root 64 Aug 27 22:46 0 -> blablalba
l-wx------ 1 root root 64 Aug 27 22:46 1 -> blablalba
l-wx------ 1 root root 64 Aug 27 22:46 2 -> blablalba
// Child process should only contain STDIN,STDOUT,STDERR or other irrelevant FDs


Actual result:
--------------
[root@localhost html]# ps -ef|grep sleep
82        1886  1881  0 22:56 pts/0    00:00:00 sleep 60
root      1890  1568  0 22:56 pts/0    00:00:00 grep --color=auto sleep

[root@localhost html]# ls -al /proc/1881/fd        // php-fpm's FDs
total 0
dr-x------ 2 root root  0 Aug 27 22:55 .
dr-xr-xr-x 9   82   82  0 Aug 27 22:55 ..
lrwx------ 1 root root 64 Aug 27 22:56 0 -> /dev/null
l-wx------ 1 root root 64 Aug 27 22:56 1 -> pipe:[26529]
lrwx------ 1 root root 64 Aug 27 22:56 10 -> socket:[26526]
l-wx------ 1 root root 64 Aug 27 22:55 2 -> pipe:[26530]
lrwx------ 1 root root 64 Aug 27 22:56 3 -> socket:[29022]
l-wx------ 1 root root 64 Aug 27 22:56 4 -> /dev/pts/0
lr-x------ 1 root root 64 Aug 27 22:56 5 -> pipe:[27765]

[root@localhost html]# ls -al /proc/1886/fd   // child process's FDs
total 0
dr-x------ 2 82 82  0 Aug 27 22:56 .
dr-xr-xr-x 9 82 82  0 Aug 27 22:56 ..
lrwx------ 1 82 82 64 Aug 27 22:56 0 -> /dev/null
l-wx------ 1 82 82 64 Aug 27 22:56 1 -> pipe:[27765]
lrwx------ 1 82 82 64 Aug 27 22:56 10 -> socket:[26526]    // FD LEAKAGE
l-wx------ 1 82 82 64 Aug 27 22:56 2 -> pipe:[26530]
lrwx------ 1 82 82 64 Aug 27 22:56 3 -> socket:[29022]     // FD LEAKAGE