linux-kernel - Re: [PATCH] iwlwifi: d3: use struct

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Date:   Tue, 04 Sep 2018 09:26:26 +0300
From:   Luciano Coelho <luciano.coelho@...el.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Intel Linux Wireless <linuxwifi@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] iwlwifi: d3: use struct_size() in kzalloc()

On Thu, 2018-08-23 at 20:15 -0500, Gustavo A. R. Silva wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
> 
> struct foo {
> 	int stuff;
>         void *entry[];
> };
> 
> instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
> 
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
> 
> instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);
> 
> This issue was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/net/wireless/intel/iwlwifi/mvm/d3.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> index 79bdae9..6960318 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> @@ -1769,8 +1769,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>  		n_matches = 0;
>  	}
>  
> -	net_detect = kzalloc(sizeof(*net_detect) +
> -			     (n_matches * sizeof(net_detect->matches[0])),
> +	net_detect = kzalloc(struct_size(net_detect, matches, n_matches),
>  			     GFP_KERNEL);
>  	if (!net_detect || !n_matches)
>  		goto out_report_nd;
> @@ -1785,8 +1784,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>  		for (j = 0; j < SCAN_OFFLOAD_MATCHING_CHANNELS_LEN; j++)
>  			n_channels += hweight8(fw_match->matching_channels[j]);
>  
> -		match = kzalloc(sizeof(*match) +
> -				(n_channels * sizeof(*match->channels)),
> +		match = kzalloc(struct_size(match, channels, n_channels),
>  				GFP_KERNEL);
>  		if (!match)
>  			goto out_report_nd;

Thanks! I applied this to our internal tree and it will reach the
mainline following our normal process.

--
Cheers,
Luca.