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SubjectRe: Overalyfs regression in 4.0
On Wed, May 13, 2015 at 09:06:26AM -0400, Josh Boyer wrote:
> Hi Miklos,
>
> Vincent reported[1] what appears to be a regression in Overlayfs with
> 4.0. This was found in the upstream docker community[2] on Ubuntu
> with 4.0.1 as well, so it is distro agnostic. The following sequence
> of commands in the bug report seems to allow one to remove a non-empty
> directory.
>
> Is this expected behavior now? I looked through the commits in 4.0
> and saw a few that might lead to a behavior change, but I am not
> familiar enough with Overalyfs to know if this was intentional or not.
>
> josh
>
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1220915
> [2] https://github.com/docker/docker/issues/13108

Good report, thanks!

Follwing patch should fix it.

Thanks,
Miklos

---
Subject: ovl: don't remove non-empty opaque directory
From: Miklos Szeredi <mszeredi@suse.cz>

When removing an opaque directory we can't just call rmdir() to check for
emptyness, because the directory will need to be replaced with a whiteout.
The replacement is done with RENAME_EXCHANGE, which doesn't check
emptyness.

Solution is just to check emptyness by reading the directory. In the
future we could add a new rename flag to check for emptyness even for
RENAME_EXCHANGE to optimize this case.

Reported-by: Vincent Batts <vbatts@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Fixes: 263b4a0fee43 ("ovl: dont replace opaque dir")
Cc: <stable@vger.kernel.org> # v4.0+
---
fs/overlayfs/dir.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)

--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -506,11 +506,25 @@ static int ovl_remove_and_whiteout(struc
struct dentry *opaquedir = NULL;
int err;

- if (is_dir && OVL_TYPE_MERGE_OR_LOWER(ovl_path_type(dentry))) {
- opaquedir = ovl_check_empty_and_clear(dentry);
- err = PTR_ERR(opaquedir);
- if (IS_ERR(opaquedir))
- goto out;
+ if (is_dir) {
+ if (OVL_TYPE_MERGE_OR_LOWER(ovl_path_type(dentry))) {
+ opaquedir = ovl_check_empty_and_clear(dentry);
+ err = PTR_ERR(opaquedir);
+ if (IS_ERR(opaquedir))
+ goto out;
+ } else {
+ LIST_HEAD(list);
+
+ /*
+ * When removing an empty opaque directory, then it
+ * makes no sense to replace it with an exact replica of
+ * itself. But emptiness still needs to be checked.
+ */
+ err = ovl_check_empty_dir(dentry, &list);
+ ovl_cache_free(&list);
+ if (err)
+ goto out;
+ }
}

err = ovl_lock_rename_workdir(workdir, upperdir);



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