linux-kernel - Re: [PATCH v3] mm: prevent endless growth of anon

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 for Android: free password hash cracker in your pocket

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

Date:	Wed, 26 Nov 2014 14:35:43 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Daniel Forrest <dan.forrest@...c.wisc.edu>
Cc:	Konstantin Khlebnikov <koct9i@...il.com>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Tim Hartrick <tim@...ecast.com>,
	Hugh Dickins <hughd@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v3] mm: prevent endless growth of anon_vma hierarchy

On Wed, 26 Nov 2014 15:05:59 -0600 Daniel Forrest <dan.forrest@...c.wisc.edu> wrote:

> On Wed, Nov 26, 2014 at 10:11:45PM +0400, Konstantin Khlebnikov wrote:
> 
> > Constantly forking task causes unlimited grow of anon_vma chain.
> > Each next child allocate new level of anon_vmas and links vmas to all
> > previous levels because it inherits pages from them. None of anon_vmas
> > cannot be freed because there might be pages which points to them.
> > 
> > This patch adds heuristic which decides to reuse existing anon_vma instead
> > of forking new one. It counts vmas and direct descendants for each anon_vma.
> > Anon_vma with degree lower than two will be reused at next fork.
> > 
> > As a result each anon_vma has either alive vma or at least two descendants,
> > endless chains are no longer possible and count of anon_vmas is no more than
> > two times more than count of vmas.
> 
> While I was working on the previous fix for this bug, Andrew Morton
> noticed that the error return from anon_vma_clone() was being dropped
> and replaced with -ENOMEM (which is not itself a bug because the only
> error return value from anon_vma_clone() is -ENOMEM).
> 
> I did an audit of callers of anon_vma_clone() and discovered an actual
> bug where the error return was being lost.  In __split_vma(), between
> Linux 3.11 and 3.12 the code was changed so the err variable is used
> before the call to anon_vma_clone() and the default initial value of
> -ENOMEM is overwritten.  So a failure of anon_vma_clone() will return
> success since err at this point is now zero.
> 
> Below is a patch which fixes this bug and also propagates the error
> return value from anon_vma_clone() in all cases.
> 
> I can send this as a separate patch, but maybe it would be easier if
> you were to incorporate it into yours?
> 

I grabbed it.  A bugfix is a bugfix.
--
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/