linux-kernel - Re: [PATCH 2/2] taskstats: restrict access to user

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Date:	Thu, 30 Jun 2011 00:17:18 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Balbir Singh <bsingharora@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	David Rientjes <rientjes@...gle.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	security@...nel.org, Eric Paris <eparis@...hat.com>,
	Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH 2/2] taskstats: restrict access to user

On Wed, Jun 29, 2011 at 06:57 +0530, Balbir Singh wrote:
> On Fri, Jun 24, 2011 at 5:39 PM, Vasiliy Kulikov <segoon@...nwall.com> wrote:
> > +               task = find_task_by_vpid(s->pid);
> > +               if (!task || __task_cred(task)->euid != cred->euid) {

If consider this patch for inclusion, it also needs some check for
the listener root ability.  __task_cred(task)->euid == 0 or smth like
that.  But ptrace_task_may_access_current() is better.

> > +                       rcu_read_unlock();
> > +                       continue;
> > +               }
> > +               rcu_read_unlock();
> > +
> 
> Release the lock prior to up_read()
> 
> >                skb_next = NULL;
> >                if (!list_is_last(&s->list, &listeners->list)) {
> >                        skb_next = skb_clone(skb_cur, GFP_KERNEL);
> > @@ -199,14 +211,19 @@ static void fill_stats(struct task_struct *tsk, struct taskstats *stats)
> >  static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
> >  {
> >        struct task_struct *tsk;
> > +       int rc = -ESRCH;
> >
> >        rcu_read_lock();
> >        tsk = find_task_by_vpid(pid);
> > +       if (tsk && !ptrace_may_access(tsk, PTRACE_MODE_READ)) {
> > +               tsk = NULL;
> > +               rc = -EACCES;
> > +       }
> >        if (tsk)
> >                get_task_struct(tsk);
> >        rcu_read_unlock();
> >        if (!tsk)
> > -               return -ESRCH;
> > +               return rc;
> >        fill_stats(tsk, stats);
> >        put_task_struct(tsk);
> >        return 0;
> > @@ -224,6 +241,10 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
> >         */
> >        rcu_read_lock();
> >        first = find_task_by_vpid(tgid);
> > +       if (first && !ptrace_may_access(first, PTRACE_MODE_READ)) {
> > +               rc = -EACCES;
> > +               goto out;
> > +       }
> >
> >        if (!first || !lock_task_sighand(first, &flags))
> >                goto out;
> 
> Balbir Singh

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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