Re: [net] vhost: Use kzalloc() to allocate vhost_msg_node

Guenter Roeck
2018-05-30T03:42:12Z

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@guarana.org>
>>> Reported-by: syzbot+87cfa083e727a224754b@syzkaller.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@redhat.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;
>