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References: <20220222094742.16359-1-sgarzare@redhat.com>
In-Reply-To: <20220222094742.16359-1-sgarzare@redhat.com>
From:   Jason Wang <jasowang@redhat.com>
Date:   Wed, 23 Feb 2022 10:09:03 +0800
Message-ID: <CACGkMEtN_YO1Avi79bMyaCqLHMMpDaPvh1oVQPEMRYky_Zbugg@mail.gmail.com>
Subject: Re: [PATCH v2] vhost/vsock: don't check owner in vhost_vsock_stop()
 while releasing
To:     Stefano Garzarella <sgarzare@redhat.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        netdev <netdev@vger.kernel.org>,
        virtualization <virtualization@lists.linux-foundation.org>,
        syzbot <syzbot+1e3ea63db39f2b4440e0@syzkaller.appspotmail.com>,
        kvm <kvm@vger.kernel.org>,
        Anirudh Rayabharam <mail@anirudhrb.com>,
        syzbot+3140b17cb44a7b174008@syzkaller.appspotmail.com,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Mike Christie <michael.christie@oracle.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        stable@vger.kernel.org
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On Tue, Feb 22, 2022 at 5:47 PM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> vhost_vsock_stop() calls vhost_dev_check_owner() to check the device
> ownership. It expects current->mm to be valid.
>
> vhost_vsock_stop() is also called by vhost_vsock_dev_release() when
> the user has not done close(), so when we are in do_exit(). In this
> case current->mm is invalid and we're releasing the device, so we
> should clean it anyway.
>
> Let's check the owner only when vhost_vsock_stop() is called
> by an ioctl.
>
> When invoked from release we can not fail so we don't check return
> code of vhost_vsock_stop(). We need to stop vsock even if it's not
> the owner.
>
> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
> Cc: stable@vger.kernel.org
> Reported-by: syzbot+1e3ea63db39f2b4440e0@syzkaller.appspotmail.com
> Reported-and-tested-by: syzbot+3140b17cb44a7b174008@syzkaller.appspotmail.com
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Acked-by: Jason Wang <jasowang@redhat.com>

> ---
> v2:
> - initialized `ret` in vhost_vsock_stop [Dan]
> - added comment about vhost_vsock_stop() calling in the code and an explanation
>   in the commit message [MST]
>
> v1: https://lore.kernel.org/virtualization/20220221114916.107045-1-sgarzare@redhat.com
> ---
>  drivers/vhost/vsock.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index d6ca1c7ad513..37f0b4274113 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -629,16 +629,18 @@ static int vhost_vsock_start(struct vhost_vsock *vsock)
>         return ret;
>  }
>
> -static int vhost_vsock_stop(struct vhost_vsock *vsock)
> +static int vhost_vsock_stop(struct vhost_vsock *vsock, bool check_owner)
>  {
>         size_t i;
> -       int ret;
> +       int ret = 0;
>
>         mutex_lock(&vsock->dev.mutex);
>
> -       ret = vhost_dev_check_owner(&vsock->dev);
> -       if (ret)
> -               goto err;
> +       if (check_owner) {
> +               ret = vhost_dev_check_owner(&vsock->dev);
> +               if (ret)
> +                       goto err;
> +       }
>
>         for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
>                 struct vhost_virtqueue *vq = &vsock->vqs[i];
> @@ -753,7 +755,12 @@ static int vhost_vsock_dev_release(struct inode *inode, struct file *file)
>          * inefficient.  Room for improvement here. */
>         vsock_for_each_connected_socket(vhost_vsock_reset_orphans);
>
> -       vhost_vsock_stop(vsock);
> +       /* Don't check the owner, because we are in the release path, so we
> +        * need to stop the vsock device in any case.
> +        * vhost_vsock_stop() can not fail in this case, so we don't need to
> +        * check the return code.
> +        */
> +       vhost_vsock_stop(vsock, false);
>         vhost_vsock_flush(vsock);
>         vhost_dev_stop(&vsock->dev);
>
> @@ -868,7 +875,7 @@ static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl,
>                 if (start)
>                         return vhost_vsock_start(vsock);
>                 else
> -                       return vhost_vsock_stop(vsock);
> +                       return vhost_vsock_stop(vsock, true);
>         case VHOST_GET_FEATURES:
>                 features = VHOST_VSOCK_FEATURES;
>                 if (copy_to_user(argp, &features, sizeof(features)))
> --
> 2.35.1
>