linux-kernel - Re: Wrong DIF guard tag on ext2 write

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: <20100604153210.GE3414@quack.suse.cz>
Date:	Fri, 4 Jun 2010 17:32:10 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dave Chinner <david@...morbit.com>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	James Bottomley <James.Bottomley@...e.de>,
	Matthew Wilcox <matthew@....cx>,
	Christof Schmitt <christof.schmitt@...ibm.com>,
	Boaz Harrosh <bharrosh@...asas.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Wrong DIF guard tag on ext2 write

On Fri 04-06-10 12:02:43, Dave Chinner wrote:
> On Thu, Jun 03, 2010 at 11:46:34AM -0400, Chris Mason wrote:
> > On Wed, Jun 02, 2010 at 11:41:21PM +1000, Nick Piggin wrote:
> > > Closing the while it is dirty, while it is being written back window
> > > still leaves a pretty big window. Also, how do you handle mmap writes?
> > > Write protect and checksum the destination page after every store? Or
> > > leave some window between when the pagecache is dirtied and when it is
> > > written back? So I don't know whether it's worth putting a lot of effort
> > > into this case.
> > 
> > So, changing gears to how do we protect filesystem page cache pages
> > instead of the generic idea of dif/dix, btrfs crcs just before writing,
> > which does leave a pretty big window for the page to get corrupted.
> > The storage layer shouldn't care or know about that though, we hand it a
> > crc and it makes sure data matching that crc goes to the media.
> 
> I think the only way to get accurate CRCs is to stop modifications
> from occurring while the page is under writeback. i.e. when a page
> transitions from dirty to writeback we need to unmap any writable
> mappings on the page, and then any new modifications (either by the
> write() path or through ->fault) need to block waiting for
> page writeback to complete before they can proceed...
  Actually, we already write-protect the page in clear_page_dirty_for_io
so the first part already happens. Any filesystem can do
wait_on_page_writeback() in its ->page_mkwrite function so even the second
part shouldn't be hard. I'm just a bit worried about the performance
implications / hidden deadlocks...
  Also we'd have to wait_on_page_writeback() in ->write_begin function to
protect against ordinary writes  but that's the easy part...

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
--
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/