tree 2a569ad361c57987d74cdcf2fb058719b4205ab8
parent ef547ba8814c66c81e72ee568ff9ed9aa4ed3e16
author Konstantin Khlebnikov <koct9i@gmail.com> 1454246273 +0300
committer ChromeOS Commit Bot <chromeos-commit-bot@chromium.org> 1472835908 +0000

UPSTREAM: ovl: ignore lower entries when checking purity of non-directory entries

After rename file dentry still holds reference to lower dentry from
previous location. This doesn't matter for data access because data comes
from upper dentry. But this stale lower dentry taints dentry at new
location and turns it into non-pure upper. Such file leaves visible
whiteout entry after remove in directory which shouldn't have whiteouts at
all.

Overlayfs already tracks pureness of file location in oe->opaque.  This
patch just uses that for detecting actual path type.

Comment from Vivek Goyal's patch:

Here are the details of the problem. Do following.

$ mkdir upper lower work merged upper/dir/
$ touch lower/test
$ sudo mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=
work merged
$ mv merged/test merged/dir/
$ rm merged/dir/test
$ ls -l merged/dir/
/usr/bin/ls: cannot access merged/dir/test: No such file or directory
total 0
c????????? ? ? ? ?            ? test

Basic problem seems to be that once a file has been unlinked, a whiteout
has been left behind which was not needed and hence it becomes visible.

Whiteout is visible because parent dir is of not type MERGE, hence
od->is_real is set during ovl_dir_open(). And that means ovl_iterate()
passes on iterate handling directly to underlying fs. Underlying fs does
not know/filter whiteouts so it becomes visible to user.

Why did we leave a whiteout to begin with when we should not have.
ovl_do_remove() checks for OVL_TYPE_PURE_UPPER() and does not leave
whiteout if file is pure upper. In this case file is not found to be pure
upper hence whiteout is left.

So why file was not PURE_UPPER in this case? I think because dentry is
still carrying some leftover state which was valid before rename. For
example, od->numlower was set to 1 as it was a lower file. After rename,
this state is not valid anymore as there is no such file in lower.

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Reported-by: Viktor Stanchev <me@viktorstanchev.com>
Suggested-by: Vivek Goyal <vgoyal@redhat.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=109611
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org>
(cherry picked from commit 45d11738969633ec07ca35d75d486bf2d8918df6)
Signed-off-by: Daniel Wang <wonderfly@google.com>
TEST=Built images with and without the fix, ran the test embedded in the
  original commit message, and verified the problem was gone with the fix.
BUG=b:31226388

Change-Id: Ie97740db9ca56914f62f5df9469a37a8a7210e1b
Reviewed-on: https://chromium-review.googlesource.com/379695
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Commit-Queue: Daniel Wang <wonderfly@google.com>
Tested-by: Daniel Wang <wonderfly@google.com>