Re: [PATCH] uprobes: Fix limiting un-nested return probes

[Hemant]

Hi Oleg,

On 09/09/2013 08:25 PM, Oleg Nesterov wrote:
> On 09/09, Anton Arapov wrote:
> > On Sun, Sep 08, 2013 at 06:32:32PM +0200, Oleg Nesterov wrote:
> > > Not sure, but I can be easily wrong... afaics we need something like below, no?
> > > Anton?
> > Oleg, your guess is correct.
> >
> > My original intention was to limit by depth the chained only probes. But later,
> > after your review, we've decided /based on safety concerns/ to limit it hard.
> Chained or not, we allocate return_instance every time, so we certainly
> need to account to limit the depth unconditionally. Unless we reuse the
> same return_instance if chained, but this is another story.

Hmm, agreed. Thanks for the description.

> > The decrement 'utask->depth--;' in my own tree is above the 'if (!chained)'
> > check. I think it got mangled somehow when I rebased the code before I sent it
> > to lkml.
> OK, thanks, I'll write the changelog and re-send the patch below.
>
> > Anton.
> >
> >
> > > Oleg.
> > >
> > > --- x/kernel/events/uprobes.c
> > > +++ x/kernel/events/uprobes.c
> > > @@ -1682,12 +1682,10 @@ static bool handle_trampoline(struct pt_
> > >   		tmp = ri;
> > >   		ri = ri->next;
> > >   		kfree(tmp);
> > > +		utask->depth--;
> > >
> > >   		if (!chained)
> > >   			break;
> > > -
> > > -		utask->depth--;
> > > -
> > >   		BUG_ON(!ri);
> > >   	}


--
Thanks
Hemant

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