netdev - Re: [net] vhost: Use kzalloc() to allocate vhost_msg

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Date:   Tue, 29 May 2018 20:42:06 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Kevin Easton <kevin@...rana.org>, Jason Wang <jasowang@...hat.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [net] vhost: Use kzalloc() to allocate vhost_msg_node

On 05/29/2018 08:01 PM, Michael S. Tsirkin wrote:
> On Tue, May 29, 2018 at 03:19:08PM -0700, Guenter Roeck wrote:
>> On Fri, Apr 27, 2018 at 11:45:02AM -0400, Kevin Easton wrote:
>>> The struct vhost_msg within struct vhost_msg_node is copied to userspace,
>>> so it should be allocated with kzalloc() to ensure all structure padding
>>> is zeroed.
>>>
>>> Signed-off-by: Kevin Easton <kevin@...rana.org>
>>> Reported-by: syzbot+87cfa083e727a224754b@...kaller.appspotmail.com
>>
>> Is this patch going anywhere ?
>>
>> The patch fixes CVE-2018-1118. It would be useful to understand if and when
>> this problem is going to be fixed.
>>
>> Thanks,
>> Guenter
>>> ---
>>>   drivers/vhost/vhost.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>>> index f3bd8e9..1b84dcff 100644
>>> --- a/drivers/vhost/vhost.c
>>> +++ b/drivers/vhost/vhost.c
>>> @@ -2339,7 +2339,7 @@ EXPORT_SYMBOL_GPL(vhost_disable_notify);
>>>   /* Create a new message. */
>>>   struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
>>>   {
>>> -	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
>>> +	struct vhost_msg_node *node = kzalloc(sizeof *node, GFP_KERNEL);
>>>   	if (!node)
>>>   		return NULL;
>>>   	node->vq = vq;
> 
> As I pointed out, we don't need to init the whole structure. The proper
> fix is thus (I think) below.
> 
> Could you use your testing infrastructure to confirm this fixes the issue?
> 

Sorry, I don't have the means to test the fix.

Guenter

> Thanks!
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index f3bd8e941224..58d9aec90afb 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2342,6 +2342,9 @@ struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
>   	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
>   	if (!node)
>   		return NULL;
> +
> +	/* Make sure all padding within the structure is initialized. */
> +	memset(&node->msg, 0, sizeof node->msg);
>   	node->vq = vq;
>   	node->msg.type = type;
>   	return node;
>