Re: [PATCH] new setprocuid syscall

[Peter Samuelson <peter@cadcamlab.org>]

[BERECZ Szabolcs]
> > Race -- you need to make sure the task_struct doesn't disappear out
> > from under you.
> 
> Yes, but we need a write_lock, not a read_lock.

No, it's a read_lock because it is locking the task *list*, which is
not being changed.  The only thing being changed is data within a task
struct.  The lock is merely to prevent the task itself from
disappearing.

> We need a userspace tool, because we must check if the user, who want
> to change the uid, knows the other user's passwd.
> Or what if user1 want to change user2's process to user3 uid?

That is a mere 'sudo'-type issue -- just a matter of figuring out who
has the right to do this to whom and under what circumstances.  Root,
in any case, can do the job without a special tool.

Anyhow, according to Alan bad things can happen if the uid set is
changed unexpectedly.  I assume he means certain permissions checks
could be confused by accessing ->euid more than once and getting
different answers.  If so, I agree that this is a bad idea....

Peter