netdev - Re: [PATCH] vhost/vsock: don't check owner in vhost_vsock

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Date:   Mon, 21 Feb 2022 16:22:40 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Mike Christie <michael.christie@...cle.com>,
        Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
        Asias He <asias@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH] vhost/vsock: don't check owner in vhost_vsock_stop()
 while releasing

On Mon, Feb 21, 2022 at 10:03:39AM -0500, Michael S. Tsirkin wrote:
>On Mon, Feb 21, 2022 at 12:49:16PM +0100, Stefano Garzarella 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.
>
>
>
>
>> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
>> Cc: stable@...r.kernel.org
>> Reported-by: syzbot+1e3ea63db39f2b4440e0@...kaller.appspotmail.com
>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>> ---
>>  drivers/vhost/vsock.c | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> index d6ca1c7ad513..f00d2dfd72b7 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;
>>
>>  	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 +755,7 @@ 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);
>
>Let's add an explanation:
>
>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.

Do you want me to send a v2 by adding this as a comment in the code?

Thanks,
Stefano