Re: [UM-LINUX] user privilege for using scheduling commands

[as]

Hi Rob,

Thanks for the input. We tried this but it seemed to drop some other
privileges as well (could be some mistake on our part).

But actually this is not what we want. We want to allow this
particular user to have the necessary privileges to use scheduling,
but we don't to give him root access. I'm guessing there must be some
way to give that user the necessary privileges.

Thanks,
Aravind.

On 1/10/07, Rob Sherwood <[EMAIL PROTECTED]> wrote:

On Wed, Jan 10, 2007 at 01:22:45PM -0500, as wrote:
> [sorry for duplicate posting]
>
> Hi,
>
> I'm trying to use sched_setscheduler() to increase the priority of a
> process but I get this error
>
> sched_setscheduler() failed: Operation not permitted
>
> I understand that the process that is calling this function needs to be
> privileged, but I don't want to run this as root. How do I elevate the
> privilege of the process or the user calling this process?
>
> I'm using Debian.

The "correct" way to do this is for the process you're running to be setuid 
root,
to call sched_setscheduler(), then use setuid(getuid()) to drop priviledges.

There is probably a better way to find the right user to setuid() back to, but 
this
is the code I use (that handles the seperate case of when I invoke this as a 
`sudo -s`
root user):

void drop_priviledges()
{
        uid_t uid;
        gid_t gid;
        char * user;
        struct passwd * pw;
        int err;

        uid=getuid();
        gid=getgid();
        if((uid == 0)||(gid==0))        // we are probably in a sudo_shell
        {
                user = getenv("USER");
                if((!user)||(!strcmp(user,"root")))
                {
                        user = getenv("SUDO_USER");
                }
                if(!user)
                {
                        sidecarlog(LOGCRIT,"failed to drop priviledges\n");
                        return;
                }
                pw = getpwnam(user);
                if(!pw)
                {
                        sidecarlog(LOGCRIT,"failed to drop priviledges: 
getpwnam()\n");
                        return;
                }
                uid=pw->pw_uid;
                gid=pw->pw_gid;
                if(uid == 0)
                {
                        sidecarlog(LOGCRIT,"failed to drop priviledges: uid still 
0()\n");
                        return;
                }
        }
        setgid(gid);            // who cares if setgid fails
        err = setuid(uid);
        if(err)
        {
                sidecarlog(LOGCRIT,"failed to drop priviledges: setuid(): 
%s\n",strerror(errno));
        }
        else
        {
                sidecarlog(LOGINFO,"dropped priviledges to uid %d gid 
%d\n",uid,gid);
        }
}