spawn a process with a different user

Applications Programming
1

Hello Everyone:

I have the following code

int main()
{
   system("/usr/OtherUser/bin/runX");
  return 0;
}

runX must be executed with privileges from another user, how could I do that? I know the password for such user.

Thanks in advance

2

There is su, but I am not sure if su reads sdin for password (ssh2 reads /dev/tty, so you need a tty generating wrapper like expect):

 
system( "su - user -c /usr/OtherUser/bin/runX");

You can use rsh/ssh/ssh2 trusted access:

system( "ssh2 -n user@localhost /usr/OtherUser/bin/runX");
3

Hello DGPickett, Thanks for quick response

su does read from stdin, unfortunately seems stdin is flushed before su prompts for the password, so I must wait for two seconds before entering the password but I don't know how.

Thanks again

4

For obvious security reasons, it doesn't, just like any other sane command that takes a password.

1 Like
5

Let's assume you not trying to hack a privileged account...
can you make /usr/OtherUser/bin/runX setuid.

And give yourself group execute?

1 Like
6

Two ideas that comes to my mind:

  • why should the runX be run with the priviledges of OtherUser. If the reason is because of files permissions, a better solution could involve putting User and OtherUser in the same group
  • If you still need to runX as OtherUser, I would recommend to use sudo (instead of su). You can configure sudo to run the program as OtherUser from User without password query

HTH,
Lo�c

1 Like
7

The ssh seems like overkill but is more secure. Two seconds, oh whoop!

 
system( "(sleep 3;echo the_password)|su - -c /usr/OtherUser/bin/runX" );
8

DGPickett, that won't work. su doesn't read stdin, and really shouldn't read stdin. Besides, you're putting the password in plaintext in a file for easy grepping by anyone.

9

Well, someone said it did, so I humored them. :smiley:

The PW could be in an env var, but of course then it will be in every core dump and has to be set somewhere!

The ssh2 trusted user Public-Private Key passwordless authentication is my recommendation, as sometimes changing user also means changing host!

We never mentioned writing a set-uid executable, but that is usually too much of a pain! Hidden trick is cc -R to locate shared objects without environment.