linux-ext4 - Re: [PATCH 4/7] ext4: fsync should wait for DIO writers

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: <20120913123632.GA13319@gmail.com>
Date:	Thu, 13 Sep 2012 20:36:32 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
	wenqing.lz@...bao.com
Subject: Re: [PATCH 4/7] ext4: fsync should wait for DIO writers

On Thu, Sep 13, 2012 at 03:01:25PM +0400, Dmitry Monakhov wrote:
> On Thu, 13 Sep 2012 18:46:21 +0800, Zheng Liu <gnehzuil.liu@...il.com> wrote:
> > On Sun, Sep 09, 2012 at 09:27:11PM +0400, Dmitry Monakhov wrote:
> > > fsync and punch_hole are the places where we have to wait for all
> > > existing writers (writeback, aio, dio), but currently we simply
> > > flush pended end_io request which is not sufficient.
> > > Even more i_mutex is not holded while punch_hole which obviously
> > > result in dangerous data corruption due to write-after-free.
> > 
> > Hi Dmitry,
> > 
> > Lukas already has a patch to take i_mutex locking before punching a
> > hole.  Just a reminding. :-)
> Yes, i've found it after patch was submitted, but this bug make me
> nervous a bit because we have broken punch_hole implementation
> long time ago, it allow to destroy data easily, user are able to
> call it if has WR permission for a file.
> So if you ask be i'll vote for hide it under CAP_SYS_RESOURCE until
> proper implementation appears.
> Same it true for EXT4_IO_MOVE_EXT because it allow to kernel panic
> since v2.6.30-6558-g748de67, so all primary distros (RH6,Deb6) are
> affected :( 

IMHO, it will be better when this patch is applied, and I prefer to fix
the problem rather than hidding it using CAP_SYS_RESOURCE. ;-)

Regards,
Zheng
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html