Re: [PATCH] security: Yama LSM

[Kees Cook]

Hi Tetsuo,

On Tue, Jun 22, 2010 at 09:28:37AM +0900, Tetsuo Handa wrote:
> Kees Cook wrote:
> > +       /* require ptrace target be a child of ptracer on attach */
> > +       if (mode == PTRACE_MODE_ATTACH && ptrace_scope &&
> > +           !capable(CAP_SYS_PTRACE)) {
> > +               struct task_struct *walker = child;
> > +
> > +               read_lock(&tasklist_lock);
> 
> Holding tasklist_lock does not imply rcu protection.
> Don't you need rcu_read_lock() like setpriority() and getppid()?

You're totally right, thanks for the catch!  Looks like setpriority() does
a similar kind of thing, so I've wrapped the whole thing in rcu_ now:

...
+               rcu_read_lock();
                read_lock(&tasklist_lock);
                while (walker->pid > 0) {
...
                        rc = -EPERM;
                read_unlock(&tasklist_lock);
+               rcu_read_unlock();
...


-Kees

-- 
Kees Cook
Ubuntu Security Team
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