linux-kernel - Re: [PATCH v5 3.1.0-rc4-tip 18/26] uprobes: slot allocation.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 27 Sep 2011 18:15:00 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 18/26]   uprobes: slot allocation.

* Peter Zijlstra <peterz@...radead.org> [2011-09-27 14:18:52]:

> On Tue, 2011-09-20 at 17:33 +0530, Srikar Dronamraju wrote:
> > +static struct uprobes_xol_area *xol_alloc_area(void)
> > +{
> > +       struct uprobes_xol_area *area = NULL;
> > +
> > +       area = kzalloc(sizeof(*area), GFP_KERNEL);
> > +       if (unlikely(!area))
> > +               return NULL;
> > +
> > +       area->bitmap = kzalloc(BITS_TO_LONGS(UINSNS_PER_PAGE) * sizeof(long),
> > +                                                               GFP_KERNEL);
> > +
> > +       if (!area->bitmap)
> > +               goto fail;
> > +
> > +       init_waitqueue_head(&area->wq);
> > +       spin_lock_init(&area->slot_lock);
> > +       if (!xol_add_vma(area) && !current->mm->uprobes_xol_area) {
> 
> So what happens if xol_add_vma() succeeds, but we find
> ->uprobes_xol_area set?
> 
> > +               task_lock(current);
> > +               if (!current->mm->uprobes_xol_area) {
> 
> Having to re-test it under this lock seems to suggest it could.
> 
> > +                       current->mm->uprobes_xol_area = area;
> > +                       task_unlock(current);
> > +                       return area;
> 
> This function would be so much easier to read if the success case (this
> here I presume) would not be nested 2 deep.
> 
> > +               }
> > +               task_unlock(current);
> > +       }
> 
> at which point you could end up with two extra vmas? Because there's no
> freeing of the result of xol_add_vma().
> 

Agree, we need to unmap the vma in that case.

> > +fail:
> > +       kfree(area->bitmap);
> > +       kfree(area);
> > +       return current->mm->uprobes_xol_area;
> > +} 

-- 
Thanks and Regards
Srikar

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/