linux-kernel - Re: [PATCH 5/5] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages

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]

Message-ID: <alpine.LNX.2.00.1212042211340.892@eggly.anvils>
Date:	Tue, 4 Dec 2012 22:28:33 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Mel Gorman <mgorman@...e.de>
cc:	Tommi Rantala <tt.rantala@...il.com>,
	Stable <stable@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Jones <davej@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 5/5] mempolicy: fix a memory corruption by refcount
 imbalance in alloc_pages_vma()

On Tue, 4 Dec 2012, Hugh Dickins wrote:
> 
> Yes, your patch fixes it Mel, but I prefer it as below, with a couple
> of mods: removing the no longer true comment, and leaving shmem_swapin()
> alone with just a comment.  It appears to be the job of the rather weird
> mpol_cond_copy() to drop the reference on the original mempolicy, and
> clear MPOL_F_SHARED so the copy won't need one (it's trying to cope with
> the fact that swapin_readahead will make an unknown number of calls to
> alloc_page_vma).  So I'd rather not add another mpol_cond_put there,
> whose cond will never be met.

Hold on, ignore that patch for now, I think I had my priorities
upside down: it would be better for shmem_swapin() to behave as
you proposed, and we delete the mpol_cond_copy() weirdness instead.

Your 00442ad04a5e changed alloc_pages_vma() to keep its refcounting
in balance, so it now does not matter that swapin_readahead() makes
an unknown number of calls to it: we should simply take a reference
before and drop it after, just as you do in shmem_alloc_page().

I'd still like to revisit alloc_page_vma(), and its refcount
manipulations do now appear redundant; but changing that is not
something I want to get into in a last minute rush.  But getting rid
of mpol_cond_copy() should be safe and clear, I'll test that out now
and reply with an updated patch (or else admit I got confused).

Hugh
--
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/