Re: [PATCH v6 00/28] fs: fixes for serious clone/dedupe problems

Dave Chinner
2018-10-22T12:54:36Z

On Mon, Oct 22, 2018 at 01:21:12PM +1100, Dave Chinner wrote:
> On Sun, Oct 21, 2018 at 09:15:03AM -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.
> > I added a few more cleanups to the xfs code per reviewer suggestions.
> >
> > So, here's the whole giant pile of patches[1] that fix all the problems.
> > This branch is against current upstream (4.19-rc8). The patch
> > "generic: test reflink side effects" recently sent to fstests exercises
> > the fixes in this series. Tests are in [2].
>
> Ok, so now that all the patches (other than the ocfs2 bits) have been
> reviewed, how do we want to merge this? I can take it through the
> XFS tree given that there is a bit of XFS changes that needs to be
> co-ordinated with it, or should it go through some other tree?

Ok, this is a bit of a mess. the patches do not merge cleanly to a
4.19-rc1 base kernel because of all the changes to
include/linux/fs.h that have hit the tree after this. There's also
failures against Documentation/filesystems/fs.h

IOWs, it's not going to get merged through the main XFS tree because
I don't have the patience to resolve all the patch application
failures, then when it comes to merge make sure all the merge
failures end up being resolved correctly.

So if I take it through the XFS tree, it will being a standalone
branch based on 4.19-rc8 and won't hit linux-next until after the
first XFS merge when I can rebase the for-next branch...

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com