linux-kernel - Re: [PATCH][next] net: hinic: fix comparison of a uint16

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Date:   Thu, 24 Aug 2017 12:29:51 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     Aviad Krawczyk <aviad.krawczyk@...wei.com>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] net: hinic: fix comparison of a uint16_t type with
 -1

On Thu, Aug 24, 2017 at 09:54:03AM +0100, Colin Ian King wrote:
> On 24/08/17 09:48, Aviad Krawczyk wrote:
> > On 8/23/2017 6:39 PM, Colin King wrote:
> >> From: Colin Ian King <colin.king@...onical.com>
> >>
> >> The comparison of hw_ioctxt.rx_buf_sz_idx == -1 is always false because
> >> rx_buf_sz_idx is a uint16_t. Fix this by explicitly casting -1 to uint16_t.
> >>
> >> Detected by CoverityScan, CID#1454559 ("Operands don't affect result")
> >>
> >> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> >> ---
> >>  drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c b/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c
> >> index 09dec6de8dd5..71e26070fb7f 100644
> >> --- a/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c
> >> +++ b/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c
> >> @@ -352,7 +352,7 @@ static int set_hw_ioctxt(struct hinic_hwdev *hwdev, unsigned int rq_depth,
> >>  		}
> >>  	}
> >>  
> >> -	if (hw_ioctxt.rx_buf_sz_idx == -1)
> >> +	if (hw_ioctxt.rx_buf_sz_idx == (uint16_t)-1)
> >>  		return -EINVAL;
> >>  
> >>  	hw_ioctxt.sq_depth  = ilog2(sq_depth);
> >>
> > 
> > Many thanks, Colin.
> > I prefer to avoid casting when possible, what do you think about replacing the condition by:
> > 
> > if (rx_buf_sz_table[i].sz != HINIC_RX_BUF_SZ)
> > 	return -EINVAL;
> > 
> 
> Does that work as expected when rx_buf_sz_table[i].sz == -1?

No it doesn't.  Please, don't ask rhetorical questions.  I have a
toddler and I constantly ask him toddler level questions and it drives
me nuts that all the adults in the room will answer me...  "Yes, I
already know that's a cow.  I was quizing my son.  But thank you!"
Meanwhile I can't resist answering questions myself...

The code looks like this:

drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c
   345          hw_ioctxt.rq_depth  = ilog2(rq_depth);
   346  
   347          for (i = 0; ; i++) {
   348                  if ((rx_buf_sz_table[i].sz == HINIC_RX_BUF_SZ) ||
   349                      (rx_buf_sz_table[i].sz == -1)) {
   350                          hw_ioctxt.rx_buf_sz_idx = rx_buf_sz_table[i].idx;
   351                          break;
   352                  }
   353          }
   354  
   355          if (hw_ioctxt.rx_buf_sz_idx == -1)
   356                  return -EINVAL;
   357  

The loop doesn't make sense.  We are looping through rx_buf_sz_table[]
until we hit 2048 or -1.  But 2048 comes first so we always get there
and break.

We may as well replace all that code with:

		hw_ioctxt.rx_buf_sz_idx = 11;

Something is very wrong.

regards,
dan carpenter