The patch titled
Subject: vfs: allow dedupe of user owned read-only files
has been added to the -mm tree. Its filename is
vfs-allow-dedupe-of-user-owned-read-only-files.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/vfs-allow-dedupe-of-user-owned-read-only-files.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/vfs-allow-dedupe-of-user-owned-read-only-files.patch
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From: Mark Fasheh <mfasheh@xxxxxxx>
Subject: vfs: allow dedupe of user owned read-only files
Patch series "vfs: fix dedupe permission check", v6.
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 file if the user
owns it or otherwise would be allowed to write to it.
Current 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 other problem we have is also related to forcing the user to open
target files for write - A process trying to exec a file currently being
deduped gets ETXTBUSY. The answer (as above) is to allow them to open the
targets ro - root can already do this. There was a patch from Adam
Borowski to fix this back in 2016:
https://lkml.org/lkml/2016/7/17/130
which I have incorporated into my changes.
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).
One way I tested these patches was to make non-root owned files with
read-only permissions and see if I could dedupe them as the owning user.
For example, the following script fails on an unpatched kernel and
succeeds with the patches applied.
TESTDIR=/btrfs
USER=mfasheh
rm -f $TESTDIR/file*
dd if=/dev/zero of=$TESTDIR/file1 count=1024 bs=1024
dd if=/dev/zero of=$TESTDIR/file2 count=1024 bs=1024
chown $USER $TESTDIR/file*
chmod 444 $TESTDIR/file*
# open file* for read and dedupe
sudo -u $USER duperemove -Ad $TESTDIR/file*
Lastly, I have an update to the fi_deduperange manpage to reflect these
changes.
This patch (of 2):
The permission check in vfs_dedupe_file_range_one() is too coarse - We
only allow dedupe of the destination file if the user is root, or they
have the file open for write.
This effectively limits a non-root user from deduping their own read-only
files. In addition, the write file descriptor that the user is forced to
hold open can prevent execution of files. As file data during a dedupe
does not change, the behavior is unexpected and this has caused a number
of issue reports. For an example, see:
https://github.com/markfasheh/duperemove/issues/129
So change the check so we allow dedupe on the target if:
- the root or admin is asking for it
- the process has write access
- the owner of the file is asking for the dedupe
- the process could get write access
That way users can open read-only and still get dedupe.
Link: http://lkml.kernel.org/r/20180910232118.14424-2-mfasheh@xxxxxxx
Signed-off-by: Mark Fasheh <mfasheh@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Cc: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/read_write.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
--- a/fs/read_write.c~vfs-allow-dedupe-of-user-owned-read-only-files
+++ a/fs/read_write.c
@@ -1964,6 +1964,20 @@ out_error:
}
EXPORT_SYMBOL(vfs_dedupe_file_range_compare);
+/* Check whether we are allowed to dedupe the destination file */
+static bool allow_file_dedupe(struct file *file)
+{
+ if (capable(CAP_SYS_ADMIN))
+ return true;
+ if (file->f_mode & FMODE_WRITE)
+ return true;
+ if (uid_eq(current_fsuid(), file_inode(file)->i_uid))
+ return true;
+ if (!inode_permission(file_inode(file), MAY_WRITE))
+ return true;
+ return false;
+}
+
int vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
struct file *dst_file, loff_t dst_pos, u64 len)
{
@@ -1978,7 +1992,7 @@ int vfs_dedupe_file_range_one(struct fil
goto out_drop_write;
ret = -EINVAL;
- if (!(capable(CAP_SYS_ADMIN) || (dst_file->f_mode & FMODE_WRITE)))
+ if (!allow_file_dedupe(dst_file))
goto out_drop_write;
ret = -EXDEV;
_
Patches currently in -mm which might be from mfasheh@xxxxxxx are
vfs-allow-dedupe-of-user-owned-read-only-files.patch
vfs-dedupe-should-return-eperm-if-permission-is-not-granted.patch
