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

[Jason Wang]

On 2019/9/23 äå5:12, 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@xxxxxxxxxx]
> Sent: Monday, September 23, 2019 4:07 PM
> To: wangxu (AE) <wangxu72@xxxxxxxxxx>
> Cc: jasowang@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> 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@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
>
> 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