Re: [PATCH] fsdax: unshare: zero destination if srcmap is HOLE or UNWRITTEN

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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@xxxxxxxxxxx> wrote:
> > 
> > > 
> > > 
> > > 在 2023/3/23 7:03, Andrew Morton 写道:
> > > > On Wed, 22 Mar 2023 11:11:09 +0000 Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx> 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?



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