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

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Message-Id: <1464112523-3701-19-git-send-email-kamal@canonical.com>
Date:	Tue, 24 May 2016 10:54:48 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Miklos Szeredi <mszeredi@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 18/53] vfs: rename: check backing inode being equal

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

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

From: Miklos Szeredi <mszeredi@...hat.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@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.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