Re: [PATCH] sanitize task->comm to avoid leaking escape codes

john stultz
2010-06-29T22:32:21Z

On Tue, 2010-06-29 at 07:58 +0300, Artem Bityutskiy wrote:
> On Wed, 2010-06-23 at 21:41 +0200, Oleg Nesterov wrote:
> > On 06/23, Kees Cook wrote:
> > >
> > > @@ -956,7 +957,15 @@ void set_task_comm(struct task_struct *tsk, char *buf)
> > > */
> > > memset(tsk->comm, 0, TASK_COMM_LEN);
> > > wmb();
> >
> > Off-topic. I'd wish I could understand this barrier. Since the lockless
> > reader doesn't do rmb() I don't see how this can help.
>
> This wmb() looks wrong to me as well. To achieve what the comment in
> this function says, it should be smp_wmb() and we should have smp_rmb()
> in the reading side, AFAIU.
>
> > OTOH, I don't
> > understand why it is needed, we never change ->comm[TASK_COMM_LEN-1] == '0'.
>
> I think the idea was that readers can see incomplete names, but not
> messed up names, consisting of old and new ones.

Yes, that was the intent, but I do see how it is unnecessary.

So I'm fine with it and the memset being removed.

Thanks for catching this!
-john