Re: [PATCH 2/2] vdpa/mlx5: Fix possible failure in umem size calculation

[Eli Cohen]

On Sun, May 30, 2021 at 04:05:57AM -0400, Michael S. Tsirkin wrote:
> On Sun, May 30, 2021 at 09:32:14AM +0300, Eli Cohen wrote:
> > umem size is a 32 bit unsigned value so assigning it to an int could
> > cause false failures. Set the calculated value inside the function and
> > modify function name to reflect the fact it updates the size.
> > 
> > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> > Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
> 
> could you clarify the impact of the bug please?
> 

This was found by code revew. I did not see it causing trouble becuase
umem sizes are small enough to fit in int. Nevertheless it's a bug that
deserves a fix.

> 
> > ---
> >  drivers/vdpa/mlx5/net/mlx5_vnet.c | 15 +++++----------
> >  1 file changed, 5 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > index 53312f0460ad..fdf3e74bffbd 100644
> > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > @@ -610,8 +610,8 @@ static void cq_destroy(struct mlx5_vdpa_net *ndev, u16 idx)
> >  	mlx5_db_free(ndev->mvdev.mdev, &vcq->db);
> >  }
> >  
> > -static int umem_size(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq, int num,
> > -		     struct mlx5_vdpa_umem **umemp)
> > +static void set_umem_size(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq, int num,
> > +			  struct mlx5_vdpa_umem **umemp)
> >  {
> >  	struct mlx5_core_dev *mdev = ndev->mvdev.mdev;
> >  	int p_a;
> > @@ -634,7 +634,7 @@ static int umem_size(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq
> >  		*umemp = &mvq->umem3;
> >  		break;
> >  	}
> > -	return p_a * mvq->num_ent + p_b;
> > +	(*umemp)->size = p_a * mvq->num_ent + p_b;
> >  }
> >  
> >  static void umem_frag_buf_free(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_umem *umem)
> > @@ -650,15 +650,10 @@ static int create_umem(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
> >  	void *in;
> >  	int err;
> >  	__be64 *pas;
> > -	int size;
> >  	struct mlx5_vdpa_umem *umem;
> >  
> > -	size = umem_size(ndev, mvq, num, &umem);
> > -	if (size < 0)
> > -		return size;
> > -
> > -	umem->size = size;
> > -	err = umem_frag_buf_alloc(ndev, umem, size);
> > +	set_umem_size(ndev, mvq, num, &umem);
> > +	err = umem_frag_buf_alloc(ndev, umem, umem->size);
> >  	if (err)
> >  		return err;
> >  
> > -- 
> > 2.31.1
>