From: Greg Kurz groug@kaod.org
commit e3a43f2a95393000778f8f302d48795add2fc4a8 upstream.
As soon as fuse_dentry_automount() does up_write(&sb->s_umount), the superblock can theoretically be killed. If this happens before the submount was added to the &fc->mounts list, fuse_mount_remove() later crashes in list_del_init() because it assumes the submount to be already there.
Add the submount before dropping sb->s_umount to fix the inconsistency. It is okay to nest fc->killsb under sb->s_umount, we already do this on the ->kill_sb() path.
Signed-off-by: Greg Kurz groug@kaod.org Fixes: bf109c64040f ("fuse: implement crossmounts") Cc: stable@vger.kernel.org # v5.10+ Reviewed-by: Max Reitz mreitz@redhat.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/fuse/dir.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -347,15 +347,15 @@ static struct vfsmount *fuse_dentry_auto goto out_put_sb; }
+ down_write(&fc->killsb); + list_add_tail(&fm->fc_entry, &fc->mounts); + up_write(&fc->killsb); + sb->s_flags |= SB_ACTIVE; fsc->root = dget(sb->s_root); /* We are done configuring the superblock, so unlock it */ up_write(&sb->s_umount);
- down_write(&fc->killsb); - list_add_tail(&fm->fc_entry, &fc->mounts); - up_write(&fc->killsb); - /* Create the submount */ mnt = vfs_create_mount(fsc); if (IS_ERR(mnt)) {