Re: [PATCH v3] ethtool: avoiding integer overflow in ethtool_phys_id()

[Alexander Lobakin <alexandr.lobakin@intel.com>]

From: Maxim Korotkov <korotkov.maxim.s@gmail.com>
Date: Tue, 22 Nov 2022 15:29:01 +0300

> The value of an arithmetic expression "n * id.data" is subject
> to possible overflow due to a failure to cast operands to a larger data
> type before performing arithmetic. Used macro for multiplication instead
> operator for avoiding overflow.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>

Reviewed-by: Alexander Lobakin <alexandr.lobakin@intel.com>

> ---
>  net/ethtool/ioctl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> index 6a7308de192d..6b59e7a1c906 100644
> --- a/net/ethtool/ioctl.c
> +++ b/net/ethtool/ioctl.c
> @@ -2007,7 +2007,8 @@ static int ethtool_phys_id(struct net_device *dev, void __user *useraddr)
>  	} else {
>  		/* Driver expects to be called at twice the frequency in rc */
>  		int n = rc * 2, interval = HZ / n;
> -		u64 count = n * id.data, i = 0;
> +		u64 count = mul_u32_u32(n, id.data);
> +		u64 i = 0;
>  
>  		do {
>  			rtnl_lock();
> -- 
> 2.17.1

Some notes to the process, not the code:

1) I asked to add my Reviewed-by to v3 in the previous thread, it's
   mandatory for authors to pick-up all the tags before publishing
   a new revision;
2) when sending v2, v3, ... vN, please have a changelog in the
   commit message or right below those '---' after your SoB, that
   makes it easier to review.

Thanks,
Olek