linux-kernel - Re: msync(2) bug(?), returns AOP_WRITEPAGE

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, 16 Oct 2007 14:02:38 -0400
From:	Erez Zadok <ezk@...sunysb.edu>
To:	"Pekka Enberg" <penberg@...helsinki.fi>
Cc:	"Erez Zadok" <ezk@...sunysb.edu>,
	"Hugh Dickins" <hugh@...itas.com>, "Ryan Finnie" <ryan@...nie.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	cjwatson@...ntu.com, linux-mm@...ck.org
Subject: Re: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland 

In message <84144f020710150447o94b1babo8b6e6a647828465f@...l.gmail.com>, "Pekka Enberg" writes:
> Hi,
> 
> On 10/15/07, Erez Zadok <ezk@...sunysb.edu> wrote:
> > Pekka, with a small change to your patch (to handle time-based cache
> > coherency), your patch worked well and passed all my tests.  Thanks.
> >
> > So now I wonder if we still need the patch to prevent AOP_WRITEPAGE_ACTIVATE
> > from being returned to userland.  I guess we still need it, b/c even with
> > your patch, generic_writepages() can return AOP_WRITEPAGE_ACTIVATE back to
> > the VFS and we need to ensure that doesn't "leak" outside the kernel.
> 
> I wonder whether _not setting_ BDI_CAP_NO_WRITEBACK implies that
> ->writepage() will never return AOP_WRITEPAGE_ACTIVATE for
> !wbc->for_reclaim case which would explain why we haven't hit this bug
> before. Hugh, Andrew?
> 
> And btw, I think we need to fix ecryptfs too.

Yes, ecryptfs needs this fix too (and probably a couple of other mmap fixes
I've made to unionfs recently -- Mike Halcrow already knows :-)

Of course, running ecryptfs on top of tmpfs is somewhat odd and uncommon;
but with unionfs, users use tmpfs as the copyup branch very often.

>                                            Pekka

Erez.
-
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/