[PATCH net] net/dim: Fix int overflow

[PATCH net] net/dim: Fix int overflow

[Tal Gilboa]

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@mellanox.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

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

[Andy Gospodarek]

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@mellanox.com>

Reviewed-by: Andy Gospodarek <gospo@broadcom.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
> 

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

[David Miller]

From: Tal Gilboa <talgi@mellanox.com>
Date: Thu, 29 Mar 2018 13:53:52 +0300

> 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@mellanox.com>

Applied, thank you.