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

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Date:	Mon, 9 Sep 2013 16:55:15 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...hat.com>
Cc:	Hemant Kumar Shaw <hkshaw@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Mikhail.Kulemin@...ibm.com,
	srikar@...ux.vnet.ibm.com, peterz@...radead.org, mingo@...hat.com,
	systemtap@...rceware.org, masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH] uprobes: Fix limiting un-nested return probes

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.

> 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);
> >  	}

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