may_umount() needs namespace_sem

otherwise it races with clone_mnt() changing mnt_share/mnt_slaves

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

diff --git a/fs/namespace.c b/fs/namespace.c
index 7d70d63..461090a 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -965,10 +965,12 @@ EXPORT_SYMBOL(may_umount_tree);
 int may_umount(struct vfsmount *mnt)
 {
        int ret = 1;
+       down_read(&namespace_sem);
        spin_lock(&vfsmount_lock);
        if (propagate_mount_busy(mnt, 2))
                ret = 0;
        spin_unlock(&vfsmount_lock);
+       up_read(&namespace_sem);
        return ret;
 }