Commit e3a43f2a authored by Greg Kurz's avatar Greg Kurz Committed by Miklos Szeredi
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fuse: Fix crash if superblock of submount gets killed early 



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: default avatarGreg Kurz <groug@kaod.org>
Fixes: bf109c64 ("fuse: implement crossmounts")
Cc: stable@vger.kernel.org # v5.10+
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
parent d92d88f0

fs/fuse/dir.c

+4 −4
Original line number Diff line number Diff line
@@ -346,15 +346,15 @@ static struct vfsmount *fuse_dentry_automount(struct path *path) 
		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)) {