netdev - Re: [PATCH net] net/dim: Fix int overflow

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Message-ID: <20180329120159.GB23910@C02RW35GFVH8>
Date:   Thu, 29 Mar 2018 08:01:59 -0400
From:   Andy Gospodarek <andrew.gospodarek@...adcom.com>
To:     Tal Gilboa <talgi@...lanox.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...lanox.com>,
        Andy Gospodarek <andrew.gospodarek@...adcom.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [PATCH net] net/dim: Fix int overflow

On Thu, Mar 29, 2018 at 01:53:52PM +0300, Tal Gilboa wrote:
> When calculating difference between samples, the values
> are multiplied by 100. Large values may cause int overflow
> when multiplied (usually on first iteration).
> Fixed by forcing 100 to be of type unsigned long.
> 
> Fixes: 4c4dbb4a7363 ("net/mlx5e: Move dynamic interrupt coalescing code to include/linux")
> Signed-off-by: Tal Gilboa <talgi@...lanox.com>

Reviewed-by: Andy Gospodarek <gospo@...adcom.com>

> ---
>  include/linux/net_dim.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/net_dim.h b/include/linux/net_dim.h
> index bebeaad..29ed8fd 100644
> --- a/include/linux/net_dim.h
> +++ b/include/linux/net_dim.h
> @@ -231,7 +231,7 @@ static inline void net_dim_exit_parking(struct net_dim *dim)
>  }
>  
>  #define IS_SIGNIFICANT_DIFF(val, ref) \
> -	(((100 * abs((val) - (ref))) / (ref)) > 10) /* more than 10% difference */
> +	(((100UL * abs((val) - (ref))) / (ref)) > 10) /* more than 10% difference */
>  
>  static inline int net_dim_stats_compare(struct net_dim_stats *curr,
>  					struct net_dim_stats *prev)
> -- 
> 1.8.3.1
>