Re: [PATCH] vhost: It's better to use size_t for the 3rd parameter of vhost_exceeds_weight()

Jason Wang
2019-09-25T04:00:05Z

On 2019/9/23 下午5:12, wangxu (AE) wrote:
> Hi Michael
>
> Thanks for your fast reply.
>
> As the following code, the 2nd branch of iov_iter_advance() does not check if i->count < size, when this happens, i->count -= size may cause len exceed INT_MAX, and then total_len exceed INT_MAX.
>
> handle_tx_copy() ->
> get_tx_bufs(..., &len, ...) ->
> init_iov_iter() ->
> iov_iter_advance(iter, ...) // has 3 branches:
> pipe_advance() // has checked the size: if (unlikely(i->count < size)) size = i->count;
> iov_iter_is_discard() ... // no check.

Yes, but I don't think we use ITER_DISCARD.

Thanks

> iterate_and_advance() //has checked: if (unlikely(i->count < n)) n = i->count;
> return iov_iter_count(iter);
>
> -----Original Message-----
> From: Michael S. Tsirkin [mailto:mst@redhat.com]
> Sent: Monday, September 23, 2019 4:07 PM
> To: wangxu (AE) <wangxu72@huawei.com>
> Cc: jasowang@redhat.com; kvm@vger.kernel.org; virtualization@lists.linux-foundation.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH] vhost: It's better to use size_t for the 3rd parameter of vhost_exceeds_weight()
>
> On Mon, Sep 23, 2019 at 03:46:41PM +0800, wangxu wrote:
>> From: Wang Xu <wangxu72@huawei.com>
>>
>> Caller of vhost_exceeds_weight(..., total_len) in drivers/vhost/net.c
>> usually pass size_t total_len, which may be affected by rx/tx package.
>>
>> Signed-off-by: Wang Xu <wangxu72@huawei.com>
>
> Puts a bit more pressure on the register file ...
> why do we care? Is there some way that it can exceed INT_MAX?
>
>> ---
>> drivers/vhost/vhost.c | 4 ++--
>> drivers/vhost/vhost.h | 7 ++++---
>> 2 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index
>> 36ca2cf..159223a 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -412,7 +412,7 @@ static void vhost_dev_free_iovecs(struct vhost_dev
>> *dev) }
>>
>> bool vhost_exceeds_weight(struct vhost_virtqueue *vq,
>> - int pkts, int total_len)
>> + int pkts, size_t total_len)
>> {
>> struct vhost_dev *dev = vq->dev;
>>
>> @@ -454,7 +454,7 @@ static size_t vhost_get_desc_size(struct
>> vhost_virtqueue *vq,
>>
>> void vhost_dev_init(struct vhost_dev *dev,
>> struct vhost_virtqueue **vqs, int nvqs,
>> - int iov_limit, int weight, int byte_weight)
>> + int iov_limit, int weight, size_t byte_weight)
>> {
>> struct vhost_virtqueue *vq;
>> int i;
>> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index
>> e9ed272..8d80389d 100644
>> --- a/drivers/vhost/vhost.h
>> +++ b/drivers/vhost/vhost.h
>> @@ -172,12 +172,13 @@ struct vhost_dev {
>> wait_queue_head_t wait;
>> int iov_limit;
>> int weight;
>> - int byte_weight;
>> + size_t byte_weight;
>> };
>>
>
> This just costs extra memory, and value is never large, so I don't think this matters.
>
>> -bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int
>> total_len);
>> +bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts,
>> + size_t total_len);
>> void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs,
>> - int nvqs, int iov_limit, int weight, int byte_weight);
>> + int nvqs, int iov_limit, int weight, size_t byte_weight);
>> long vhost_dev_set_owner(struct vhost_dev *dev); bool
>> vhost_dev_has_owner(struct vhost_dev *dev); long
>> vhost_dev_check_owner(struct vhost_dev *);
>> --
>> 1.8.5.6