linux-kernel - Re: [patch V4 01/32] mm/slab: Fix broken stack trace storage

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Message-ID: <alpine.DEB.2.21.1904152320540.1806@nanos.tec.linutronix.de>
Date:   Mon, 15 Apr 2019 23:22:17 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [patch V4 01/32] mm/slab: Fix broken stack trace storage

On Mon, 15 Apr 2019, Andy Lutomirski wrote:
> On Mon, Apr 15, 2019 at 9:17 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Mon, Apr 15, 2019 at 06:07:44PM +0200, Thomas Gleixner wrote:
> > > > Looks like stack_trace.nr_entries isn't initialized?  (though this code
> > > > gets eventually replaced by a later patch)
> > >
> > > struct initializer initialized the non mentioned fields to 0, if I'm not
> > > totally mistaken.
> >
> > Hm, it seems you are correct.  And I thought I knew C.
> >
> > > > Who actually reads this stack trace?  I couldn't find a consumer.
> > >
> > > It's stored directly in the memory pointed to by @addr and that's the freed
> > > cache memory. If that is used later (UAF) then the stack trace can be
> > > printed to see where it was freed.
> >
> > Right... but who reads it?
> 
> That seems like a reasonable question.  After some grepping and some
> git searching, it looks like there might not be any users.  I found

Anymore. There was something 10y+ ago...

> SLAB_STORE_USER, but that seems to be independent.
> 
> So maybe the whole mess should just be deleted.  If anyone ever
> notices, they can re-add it better.

No objections from my side, but the mm people might have opinions.

Thanks,

	tglx