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 04:17:09 +0000 [thread overview]
Message-ID: <ZB0kRXVFXOJg0rQC@casper.infradead.org> (raw)
In-Reply-To: <4aee7cfd-09d6-43a1-3d8c-15fe5274446b@fujitsu.com>
On Fri, Mar 24, 2023 at 11:42:53AM +0800, Shiyang Ruan wrote:
>
>
> 在 2023/3/24 11:33, Matthew Wilcox 写道:
> > 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?
>
> Ok. If this happenned to a user, the HOLE or UNWRITTEN part will be old
> data of the new allocated extent because it didn't be cleared.
ie it's the data that was in whatever file happened to use that space
last, so this is a security bug because it's a data leak, and a backport
is needed, and you should have indicated that by putting a cc: stable
tag on the patch?
next prev parent reply other threads:[~2023-03-24 4:17 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
2023-03-24 3:42 ` Shiyang Ruan
2023-03-24 4:17 ` Matthew Wilcox [this message]
2023-03-24 4:28 ` Shiyang Ruan
2023-03-24 20:44 ` Andrew Morton
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