From: Greg Kurz <groug@xxxxxxxx>
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@xxxxxxxx>
Fixes: bf109c64040f ("fuse: implement crossmounts")
Cc: stable@xxxxxxxxxxxxxxx # v5.10+
Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/fuse/dir.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -346,15 +346,15 @@ 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)) {
