[PATCH 4.2.y-ckt 18/53] vfs: rename: check backing inode being equal

[Kamal Mostafa]

4.2.8-ckt11 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Miklos Szeredi <mszeredi at redhat.com>

commit 9409e22acdfc9153f88d9b1ed2bd2a5b34d2d3ca upstream.

If a file is renamed to a hardlink of itself POSIX specifies that rename(2)
should do nothing and return success.

This condition is checked in vfs_rename().  However it won't detect hard
links on overlayfs where these are given separate inodes on the overlayfs
layer.

Overlayfs itself detects this condition and returns success without doing
anything, but then vfs_rename() will proceed as if this was a successful
rename (detach_mounts(), d_move()).

The correct thing to do is to detect this condition before even calling
into overlayfs.  This patch does this by calling vfs_select_inode() to get
the underlying inodes.

Signed-off-by: Miklos Szeredi <mszeredi at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/namei.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 0402c3c..eda6dfc 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4186,7 +4186,11 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	bool new_is_dir = false;
 	unsigned max_links = new_dir->i_sb->s_max_links;
 
-	if (source == target)
+	/*
+	 * Check source == target.
+	 * On overlayfs need to look at underlying inodes.
+	 */
+	if (vfs_select_inode(old_dentry, 0) == vfs_select_inode(new_dentry, 0))
 		return 0;
 
 	error = may_delete(old_dir, old_dentry, is_dir);
-- 
2.7.4