Re: [PATCH v3 00/25] fs: fixes for serious clone/dedupe problems

Amir Goldstein
2018-10-11T08:33:57Z

On Thu, Oct 11, 2018 at 7:12 AM Darrick J. Wong <darrick.wong@oracle.com> 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.
> This branch is against 4.19-rc7 with Dave Chinner's XFS for-next branch.
> The patch "generic: test reflink side effects" recently sent to fstests
> exercises the fixes in this series. Tests are in [2].
>
> --D
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/log/?h=djwong-devel
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfstests-dev.git/log/?h=djwong-devel

I tested your branch with overlayfs over xfs.
I did not observe any failures with -g clone except for test generic/937
which also failed on xfs in my test.

I though that you forgot to mention I needed to grab xfsprogs from djwong-devel
for commit e84a9e93 ("xfs_io: dedupe command should only complain
if we don't dedupe anything"), but even with this change the test still fails:

generic/937 - output mismatch (see
/old/home/amir/src/fstests/xfstests-dev/results//generic/937.out.bad)
--- tests/generic/937.out 2018-10-11 08:23:00.630938364 +0300
+++ /old/home/amir/src/fstests/xfstests-dev/results//generic/937.out.bad
2018-10-11 10:54:40.448134832 +0300
@@ -4,8 +4,7 @@
39578c21e2cb9f6049b1cf7fc7be12a6 TEST_DIR/test-937/file2
Files 1-2 do not match (intentional)
(partial) dedupe the middle blocks together
-deduped XXXX/XXXX bytes at offset XXXX
-XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+XFS_IOC_FILE_EXTENT_SAME: Extents did not match.
Compare sections

One thing that *is* different with overlayfs test is that filefrag crashes
on this same test:

QA output created by 937
Create the original files
35ac8d7917305c385c30f3d82c30a8f6 TEST_DIR/test-937/file1
39578c21e2cb9f6049b1cf7fc7be12a6 TEST_DIR/test-937/file2
Files 1-2 do not match (intentional)
(partial) dedupe the middle blocks together
XFS_IOC_FILE_EXTENT_SAME: Extents did not match.
./tests/generic/937: line 59: 19242 Floating point exception(core
dumped) ${FILEFRAG_PROG} -v $testdir/file1 >> $seqres.full
./tests/generic/937: line 60: 19244 Floating point exception(core
dumped) ${FILEFRAG_PROG} -v $testdir/file2 >> $seqres.full

It looks like an overlayfs v4.19-rc1 regression - FIGETBSZ returns zero.
I never noticed this regression before, because none of the generic tests
are using filefrag.

Thanks,
Amir.