btrfs: prevent to set invalid default subvolid

BugLink: http://bugs.launchpad.net/bugs/1721777
commit 6d6d282932d1a609e60dc4467677e0e863682f57 upstream.

`btrfs sub set-default` succeeds to set an ID which isn't corresponding to any
fs/file tree. If such the bad ID is set to a filesystem, we can't mount this
filesystem without specifying `subvol` or `subvolid` mount options.

Fixes: 6ef5ed0d386b ("Btrfs: add ioctl and incompat flag to set the default mount subvol")
Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
Reviewed-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 8f1bfd512afced562c07099e69f6243564262b2b..9afd08539519a78ee4a9c42e3dcea39aa033f21d 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4072,6 +4072,10 @@ static long btrfs_ioctl_default_subvol(struct file *file, void __user *argp)
                ret = PTR_ERR(new_root);
                goto out;
        }
+       if (!is_fstree(new_root->objectid)) {
+               ret = -ENOENT;
+               goto out;
+       }
 
        path = btrfs_alloc_path();
        if (!path) {