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

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Date:   Mon, 7 May 2018 15:12:31 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Kevin Easton <kevin@...rana.org>, Jason Wang <jasowang@...hat.com>,
        KVM list <kvm@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH net] vhost: Use kzalloc() to allocate vhost_msg_node

On Mon, May 7, 2018 at 3:03 PM, Michael S. Tsirkin <mst@...hat.com> 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
>> ---
>>  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;
>
>
> Let's just init the msg though.
>
> OK it seems this is the best we can do for now,
> we need a new feature bit to fix it for 32 bit
> userspace on 64 bit kernels.
>
> Does the following help?

Hi Michael,

You can ask reporter (syzbot) to test:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#kmsan-bugs


> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index f3bd8e9..58d9aec 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;
>
> --
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