Re: [PATCH v2 00/25] fs: fixes for serious clone/dedupe problems

Darrick J. Wong
2018-10-10T01:06:52Z

On Wed, Oct 10, 2018 at 12:02:08PM +1100, Dave Chinner wrote:
> On Tue, Oct 09, 2018 at 05:10:38PM -0700, Darrick J. Wong wrote:
> > Hi all,
> >
> > Dave, Eric, and I have been chasing a stale data exposure bug in the XFS
> > reflink implementation, and tracked it down to reflink forgetting to do
> > some of the file-extending activities that must happen for regular
> > writes.
> >
> > We then started auditing the clone, dedupe, and copyfile code and
> > realized that from a file contents perspective, clonerange isn't any
> > different from a regular file write. Unfortunately, we also noticed
> > that *unlike* a regular write, clonerange skips a ton of overflow
> > checks, such as validating the ranges against s_maxbytes, MAX_NON_LFS,
> > and RLIMIT_FSIZE. We also observed that cloning into a file did not
> > strip security privileges (suid, capabilities) like a regular write
> > would. I also noticed that xfs and ocfs2 need to dump the page cache
> > before remapping blocks, not after.
> >
> > In fixing the range checking problems I also realized that both dedupe
> > and copyfile tell userspace how much of the requested operation was
> > acted upon. Since the range validation can shorten a clone request (or
> > we can ENOSPC midway through), we might as well plumb the short
> > operation reporting back through the VFS indirection code to userspace.
> >
> > So, here's the whole giant pile of patches[1] that fix all the problems.
> > The patch "generic: test reflink side effects" recently sent to fstests
> > exercises the fixes in this series. Tests are in [2].
>
> Can you rebase this on the for-next branch on the xfs tree which
> already contains some of the initial fixes in the series and a
> couple of other reflink/dedupe data corruption fixes? I'm planning
> on pushing them to Greg tomorrow, so you'll have to do this soon
> anyway....

<nod> I was planning to do that tomorrow, but figured I might as well
scrape for review comments in the mean time.

--D

> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com