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ovl: fix regression caused by overlapping layers detection

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Once upon a time, commit 2cac0c00a6 ("ovl: get exclusive ownership on
upper/work dirs") in v4.13 added some sanity checks on overlayfs layers.
This change caused a docker regression. The root cause was mount leaks
by docker, which as far as I know, still exist.

To mitigate the regression, commit 85fdee1eef ("ovl: fix regression
caused by exclusive upper/work dir protection") in v4.14 turned the
mount errors into warnings for the default index=off configuration.

Recently, commit 146d62e5a5 ("ovl: detect overlapping layers") in
v5.2, re-introduced exclusive upper/work dir checks regardless of
index=off configuration.

This changes the status quo and mount leak related bug reports have
started to re-surface. Restore the status quo to fix the regressions.
To clarify, index=off does NOT relax overlapping layers check for this
ovelayfs mount. index=off only relaxes exclusive upper/work dir checks
with another overlayfs mount.

To cover the part of overlapping layers detection that used the
exclusive upper/work dir checks to detect overlap with self upper/work
dir, add a trap also on the work base dir.

Link: https://github.com/moby/moby/issues/34672
Link: https://lore.kernel.org/linux-fsdevel/20171006121405.GA32700@veci.piliscsaba.szeredi.hu/
Link: https://github.com/containers/libpod/issues/3540
Fixes: 146d62e5a5 ("ovl: detect overlapping layers")
Cc: <stable@vger.kernel.org> # v4.19+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Tested-by: Colin Walters <walters@verbum.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein
2019-07-12 15:24:34 +03:00
committed by Miklos Szeredi
parent 0ecfebd2b5
commit 0be0bfd2de
3 changed files with 49 additions and 27 deletions
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2
Documentation/filesystems/overlayfs.txt
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@@ -302,7 +302,7 @@ beneath or above the path of another overlay lower layer path.
Using an upper layer path and/or a workdir path that are already used by
another overlay mount is not allowed and may fail with EBUSY. Using
partially overlapping paths is not allowed but will not fail with EBUSY.
partially overlapping paths is not allowed and may fail with EBUSY.
If files are accessed from two overlayfs mounts which share or overlap the
upper layer and/or workdir path the behavior of the overlay is undefined,
though it will not result in a crash or deadlock.