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From: Matthew Wilcox <willy@infradead.org>
To: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev,
	dan.j.williams@intel.com, jack@suse.cz, djwong@kernel.org
Subject: Re: [PATCH] fsdax: unshare: zero destination if srcmap is HOLE or UNWRITTEN
Date: Fri, 24 Mar 2023 03:33:27 +0000	[thread overview]
Message-ID: <ZB0aB7DzhzuyaM9Z@casper.infradead.org> (raw)
In-Reply-To: <a30006e8-2896-259e-293b-2a5d873d42aa@fujitsu.com>

On Fri, Mar 24, 2023 at 09:50:54AM +0800, Shiyang Ruan wrote:
> 
> 
> 在 2023/3/24 6:11, Andrew Morton 写道:
> > On Thu, 23 Mar 2023 14:50:38 +0800 Shiyang Ruan <ruansy.fnst@fujitsu.com> wrote:
> > 
> > > 
> > > 
> > > 在 2023/3/23 7:03, Andrew Morton 写道:
> > > > On Wed, 22 Mar 2023 11:11:09 +0000 Shiyang Ruan <ruansy.fnst@fujitsu.com> wrote:
> > > > 
> > > > > unshare copies data from source to destination. But if the source is
> > > > > HOLE or UNWRITTEN extents, we should zero the destination, otherwise the
> > > > > result will be unexpectable.
> > > > 
> > > > Please provide much more detail on the user-visible effects of the bug.
> > > > For example, are we leaking kernel memory contents to userspace?
> > > 
> > > This fixes fail of generic/649.
> > 
> > OK, but this doesn't really help.  I'm trying to determine whether this
> > fix should be backported into -stable kernels and whether it should be
> > fast-tracked into Linus's current -rc tree.
> > 
> > But to determine this I (and others) need to know what effect the bug
> > has upon our users.
> 
> I didn't get any bug report form users.  I just found this by running
> xfstests.  The phenomenon of this problem is: if we funshare a reflinked
> file which contains HOLE extents, the result of the HOLE extents should be
> zero but actually not (unexpectable data).

You still aren't answering the question.  If this did happen to a user,
what would they see in the file?  Random data?  Something somebody else
wrote some time ago?  A copy of /etc/passwd, perhaps?  A copy of your
credit card number?

  reply	other threads:[~2023-03-24  3:33 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-22 11:11 [PATCH] fsdax: unshare: zero destination if srcmap is HOLE or UNWRITTEN Shiyang Ruan
2023-03-22 23:03 ` Andrew Morton
2023-03-23  6:50   ` Shiyang Ruan
2023-03-23 14:59     ` Darrick J. Wong
2023-03-23 22:11     ` Andrew Morton
2023-03-24  1:50       ` Shiyang Ruan
2023-03-24  3:33         ` Matthew Wilcox [this message]
2023-03-24  3:42           ` Shiyang Ruan
2023-03-24  4:17             ` Matthew Wilcox
2023-03-24  4:28               ` Shiyang Ruan
2023-03-24 20:44                 ` Andrew Morton

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