[057/111] Btrfs: deny sys_link across subvolumes.

[Greg KH]

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: TARUISI Hiroaki <taruishi.hiroak@xxxxxxxxxxxxxx>

commit 4a8be425a8fb8fbb5d881eb55fa6634c3463b9c9 upstream.

I rebased Christian Parpart's patch to deny hard link across
subvolumes. Original patch modifies also btrfs_rename, but
I excluded it because we can move across subvolumes now and
it make no problem.
-----------------

Hard link across subvolumes should not allowed in Btrfs.
btrfs_link checks root of 'to' directory is same as root
of 'from' file. If not same, btrfs_link returns -EPERM.

Signed-off-by: TARUISI Hiroaki <taruishi.hiroak@xxxxxxxxxxxxxx>
Signed-off-by: Chris Mason <chris.mason@xxxxxxxxxx>
Acked-by: Jeff Mahoney <jeffm@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>


---
 fs/btrfs/inode.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4462,6 +4462,10 @@ static int btrfs_link(struct dentry *old
 	if (inode->i_nlink == 0)
 		return -ENOENT;
 
+	/* do not allow sys_link's with other subvols of the same device */
+	if (root->objectid != BTRFS_I(inode)->root->objectid)
+		return -EPERM;
+
 	/*
 	 * 1 item for inode ref
 	 * 2 items for dir items


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