Question

I have a CentOS 5.7 linux server and use php5.3.x.

On a pfSense system, you can restart services-that required root permissions using a php web page.

I’m trying to do something similar, I have written some php code to execute shell commands. For example, to restart the sshd service:

<?php
exec('/sbin/service sshd restart');
?>

and I tried to execute that command via exec function, but it needs root permission, but we have a apache user authority.

I have come across a few solutions:

1. “run apache with root user”
   really unsafe. I do not want to do that.
2. “apache ALL=NOPASSWD:/sbin/service to /etc/sudoers”
   I tried but and still have a problem.

Any other solutions?
Thanks for answers.

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now.. it’s interesting. i tried @refp post and it worked my local ubuntu server. But when i tried same at my cenOS vps server. It’s not working.and that is apache’s error log “rm: cannot remove `/var/lock/subsys/vsftpd’: Permission denied”

Answer 1

Read this whole post before trying it out, there are choices to be made.

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Solution using a binary wrapper (with suid bit)

1) Create a script (preferrably .sh) that contains what you want to be ran as root.

# cat > php_shell.sh <<CONTENT
  #!/bin/sh
  /sbin/service sshd restart
CONTENT

2) This file should be owned by root, and since it will later run with root permissions make sure that only root has permission to write to the file.

# chown root php_shell.sh
# chmod u=rwx,go=xr php_shell.sh

3) To run the script as root no matter what user that executes it, we will need a binary wrapper. Create one that will execute our php_shell.sh.

# cat > wrapper.c <<CONTENT
  #include <stdlib.h>
  #include <sys/types.h>
  #include <unistd.h>

  int
  main (int argc, char *argv[])
  {
     setuid (0);

     /* WARNING: Only use an absolute path to the script to execute,
      *          a malicious user might fool the binary and execute
      *          arbitary commands if not.
      * */

     system ("/bin/sh /path/to/php_shell.sh");

     return 0;
   }
CONTENT

4) Compile and set proper permissions, including the suid bit (saying that it should run with root privileges):

# gcc wrapper.c -o php_root
# chown root php_root
# chmod u=rwx,go=xr,+s php_root

php_root will now run with root permissions, and execute the commands specified in php_shell.sh.

---

If you don’t need to the option to easily change what commands that will be executed I’d recommend you to write the commands directly in wrapper.c under step 4. Then you don’t need to have a binary executing a external script executing the commands in question.

In wrapper.c, use system ("your shell command here"); to specify what commands you’d like to execute.