fs: Don't allow to create hardlink for deleted file

Add inode->i_nlink == 0 check in VFS. Some of the file systems
do this internally. A followup patch will remove those instance.
This is needed to ensure that with link by handle we don't allow
to create hardlink of an unlinked file. The check also prevent a race
between unlink and link

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 83e92bab79a6..33be51a2ddb7 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2906,7 +2906,11 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
                 return error;
 
         mutex_lock(&inode->i_mutex);
-        error = dir->i_op->link(old_dentry, dir, new_dentry);
+        /* Make sure we don't allow creating hardlink to an unlinked file */
+        if (inode->i_nlink == 0)
+                error =  -ENOENT;
+        else
+                error = dir->i_op->link(old_dentry, dir, new_dentry);
         mutex_unlock(&inode->i_mutex);
         if (!error)
                 fsnotify_link(dir, inode, new_dentry);