linux-kernel - Re: [PATCH v2 2/7] fuse: Fix crash if superblock of submount gets killed early

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Message-ID: <0daa30dc-ea49-dbe3-eac5-4b47dceb54eb@redhat.com>
Date:   Tue, 8 Jun 2021 17:08:37 +0200
From:   Max Reitz <mreitz@...hat.com>
To:     Greg Kurz <groug@...d.org>, Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        virtio-fs@...hat.com, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v2 2/7] fuse: Fix crash if superblock of submount gets
 killed early

On 04.06.21 18:11, Greg Kurz wrote:
> 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@...d.org>
> ---
>   fs/fuse/dir.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)

Reviewed-by: Max Reitz <mreitz@...hat.com>