Re: [PATCH][net-next] net/mlx4: Use array_size() helper in copy_to_user()

[Tariq Toukan]

On 9/29/2021 8:21 PM, Eric Dumazet wrote:
> On 9/29/21 3:24 AM, Tariq Toukan wrote:
> > On 9/28/2021 11:17 PM, Gustavo A. R. Silva wrote:
> > > Use array_size() helper instead of the open-coded version in
> > > copy_to_user(). These sorts of multiplication factors need
> > > to be wrapped in array_size().
> > >
> > > Link: https://github.com/KSPP/linux/issues/160
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > > ---
> > >    drivers/net/ethernet/mellanox/mlx4/cq.c | 3 ++-
> > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/ethernet/mellanox/mlx4/cq.c b/drivers/net/ethernet/mellanox/mlx4/cq.c
> > > index f7053a74e6a8..4d4f9cf9facb 100644
> > > --- a/drivers/net/ethernet/mellanox/mlx4/cq.c
> > > +++ b/drivers/net/ethernet/mellanox/mlx4/cq.c
> > > @@ -314,7 +314,8 @@ static int mlx4_init_user_cqes(void *buf, int entries, int cqe_size)
> > >                buf += PAGE_SIZE;
> > >            }
> > >        } else {
> > > -        err = copy_to_user((void __user *)buf, init_ents, entries * cqe_size) ?
> > > +        err = copy_to_user((void __user *)buf, init_ents,
> > > +                   array_size(entries, cqe_size)) ?
> > >                -EFAULT : 0;
> > >        }
> > >   
> >
> > Thanks for your patch.
> > Reviewed-by: Tariq Toukan <tariqt@xxxxxxxxxx>
>
> Not sure why avoiding size_t overflows would make this code safer.
> init_ents contains PAGE_SIZE bytes...
>
> BTW
>
> Is @entries guaranteed to be a power of two ?

Yes.

> This function seems to either copy one chunk ( <= PAGE_SIZE),
> or a number of full pages.

Exactly. No remainder handling is needed, for the reason you mentioned 
above.