__d_unalias() should refuse to move mountpoints

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 4 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 015586f1ffc..8086636bf79 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2387,14 +2387,13 @@ static struct dentry *__d_unalias(struct inode *inode,
                 struct dentry *dentry, struct dentry *alias)
 {
         struct mutex *m1 = NULL, *m2 = NULL;
-        struct dentry *ret;
+        struct dentry *ret = ERR_PTR(-EBUSY);
 
         /* If alias and dentry share a parent, then no extra locks required */
         if (alias->d_parent == dentry->d_parent)
                 goto out_unalias;
 
         /* See lock_rename() */
-        ret = ERR_PTR(-EBUSY);
         if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
                 goto out_err;
         m1 = &dentry->d_sb->s_vfs_rename_mutex;
@@ -2402,8 +2401,10 @@ static struct dentry *__d_unalias(struct inode *inode,
                 goto out_err;
         m2 = &alias->d_parent->d_inode->i_mutex;
 out_unalias:
-        __d_move(alias, dentry);
-        ret = alias;
+        if (likely(!d_mountpoint(alias))) {
+                __d_move(alias, dentry);
+                ret = alias;
+        }
 out_err:
         spin_unlock(&inode->i_lock);
         if (m2)