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Message-ID: <20090506231332.GA3756@redhat.com>
Date: Thu, 7 May 2009 01:13:32 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Chris Wright <chrisw@...s-sol.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Roland McGrath <roland@...hat.com>,
linux-kernel@...r.kernel.org, James Morris <jmorris@...ei.org>
Subject: Re: [PATCH 3/3] ptrace: do not use task_lock() for attach
On 05/06, Chris Wright wrote:
>
> * Oleg Nesterov (oleg@...hat.com) wrote:
> > + write_lock_irq(&tasklist_lock);
> > retval = -EPERM;
> > if (unlikely(task->exit_state))
> > - goto bad;
> > + goto unlock_tasklist;
> > if (task->ptrace)
> > - goto bad;
> > + goto unlock_tasklist;
>
> So, task->ptrace now protected by tasklist_lock to keep concurrent tracers
> from both attaching to same task?
Yes,
> (re-oredered)
>
> What do you think?
I think I need your help!
> What does this do for setprocattr()?
>
> task_lock(p);
> tracer = tracehook_tracer_task(p);
> if (tracer)
> ptsid = task_sid(tracer);
> task_unlock(p);
>
> Looks like it is racy.
Looks like you are right, but I don't understand selinux at all.
> cpu1 (tracer) cpu2 (tracee, changing sid)
> ------------- ---------------------------
> task_lock(tracee);
> __ptrace_may_access(tracee, ATTACH);
> task_unlock(tracee);
> task_lock(tracee)
> <security check passes> tracer = tracehook_tracer_task(tracee);
> if (tracer) <-- NULL, !tracee->ptrace
> ...
> update sid w/out checking against tracer
> write_lock_irq(&tasklist_lock);
> ...
> tracee->ptrace = PT_PTRACED;
> ...
> now we are tracing task w/ a sid
> that we didn't authorize to trace
But this can happen without this change too?
- cpu2 takes task_lock(), tracehook_tracer_task() returns NULL because
we are not traced yet.
- cpu1 does ptrace_attach() and succeds, because cpu2 didn't update sid
yet
- cpu2 continues, it doesn't check avc_has_perm() (tracer == 0) and
updates sid.
No?
Shouldn't selinux_setprocattr() take ->cred_exec_mutex, like we do in
selinux_bprm_set_creds() path?
Oleg.
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