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List:       linux-xfs
Subject:    [PATCH 0/2] vfs: better dedupe permission check
From:       Mark Fasheh <mfasheh () suse ! de>
Date:       2018-05-11 19:26:49
Message-ID: 20180511192651.21324-1-mfasheh () suse ! de
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Hi,

The following patches fix a couple of issues with the permission
check we do in vfs_dedupe_file_range().

The first patch expands our check to allow dedupe of a readonly file
if the user owns it. Existing behavior is that we'll allow dedupe only
if:

- the user is an admin (root)
- the user has the file open for write

This makes it impossible for a user to dedupe their own file set
unless they do it as root, or ensure that all files have write
permission. There's a couple of duperemove bugs open for this:

https://github.com/markfasheh/duperemove/issues/129
https://github.com/markfasheh/duperemove/issues/86

The solution is simple - we allow dedupe of the target if the user
owns it. With that patch, a user can dedupe all of their files.

The 2nd patch fixes our return code for permission denied to be
EPERM. For some reason we're returning EINVAL - I think that's
probably my fault. At any rate, we need to be returning something
descriptive of the actual problem, otherwise callers see EINVAL and
can't really make a valid determination of what's gone wrong.

This has also popped up in duperemove, mostly in the form of cryptic
error messages. Because this is a code returned to userspace, I did
check the other users of extent-same that I could find. Both 'bees'
and 'rust-btrfs' do the same as duperemove and simply report the error
(as they should).

The patches are also available in git:

git pull https://github.com/markfasheh/linux dedupe-perms

Thanks,
  --Mark
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