ovl: prevent private clone if bind mount is not allowed

Add the following checks from __do_loopback() to clone_private_mount() as
well:

 - verify that the mount is in the current namespace

 - verify that there are no locked children

Reported-by: Alois Wohlschlager <alois1@gmx-topmail.de>
Fixes: c771d683a62e ("vfs: introduce clone_private_mount()")
Cc: <stable@vger.kernel.org> # v3.18
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/namespace.c b/fs/namespace.c
index ab4174a..f79d947 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1938,6 +1938,20 @@ void drop_collected_mounts(struct vfsmount *mnt)
        namespace_unlock();
 }
 
+static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
+{
+       struct mount *child;
+
+       list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
+               if (!is_subdir(child->mnt_mountpoint, dentry))
+                       continue;
+
+               if (child->mnt.mnt_flags & MNT_LOCKED)
+                       return true;
+       }
+       return false;
+}
+
 /**
  * clone_private_mount - create a private clone of a path
  * @path: path to clone
@@ -1953,10 +1967,19 @@ struct vfsmount *clone_private_mount(const struct path *path)
        struct mount *old_mnt = real_mount(path->mnt);
        struct mount *new_mnt;
 
+       down_read(&namespace_sem);
        if (IS_MNT_UNBINDABLE(old_mnt))
-               return ERR_PTR(-EINVAL);
+               goto invalid;
+
+       if (!check_mnt(old_mnt))
+               goto invalid;
+
+       if (has_locked_children(old_mnt, path->dentry))
+               goto invalid;
 
        new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
+       up_read(&namespace_sem);
+
        if (IS_ERR(new_mnt))
                return ERR_CAST(new_mnt);
 
@@ -1964,6 +1987,10 @@ struct vfsmount *clone_private_mount(const struct path *path)
        new_mnt->mnt_ns = MNT_NS_INTERNAL;
 
        return &new_mnt->mnt;
+
+invalid:
+       up_read(&namespace_sem);
+       return ERR_PTR(-EINVAL);
 }
 EXPORT_SYMBOL_GPL(clone_private_mount);
 
@@ -2315,19 +2342,6 @@ static int do_change_type(struct path *path, int ms_flags)
        return err;
 }
 
-static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
-{
-       struct mount *child;
-       list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
-               if (!is_subdir(child->mnt_mountpoint, dentry))
-                       continue;
-
-               if (child->mnt.mnt_flags & MNT_LOCKED)
-                       return true;
-       }
-       return false;
-}
-
 static struct mount *__do_loopback(struct path *old_path, int recurse)
 {
        struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);