Re: [PATCH] wifi: iwlwifi: mvm: Fix __counted_by usage in cfg80211_wowlan_nd_*

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 19/06/24 23:12, Kees Cook wrote:
> Both struct cfg80211_wowlan_nd_match and struct cfg80211_wowlan_nd_info
> pre-allocate space for channels and matches, but then may end up using
> fewer that the full allocation. Shrink the associated counter
> (n_channels and n_matches) after counting the results. This avoids
> compile-time (and run-time) warnings from __counted_by. (The counter
> member needs to be updated _before_ accessing the array index.)
> 
> Seen with coming GCC 15:
> 
> drivers/net/wireless/intel/iwlwifi/mvm/d3.c: In function 'iwl_mvm_query_set_freqs':
> drivers/net/wireless/intel/iwlwifi/mvm/d3.c:2877:66: warning: operation on 'match->n_channels' may be undefined [-Wsequence-point]
>   2877 |                                 match->channels[match->n_channels++] =
>        |                                                 ~~~~~~~~~~~~~~~~~^~
> drivers/net/wireless/intel/iwlwifi/mvm/d3.c:2885:66: warning: operation on 'match->n_channels' may be undefined [-Wsequence-point]
>   2885 |                                 match->channels[match->n_channels++] =
>        |                                                 ~~~~~~~~~~~~~~~~~^~
> drivers/net/wireless/intel/iwlwifi/mvm/d3.c: In function 'iwl_mvm_query_netdetect_reasons':
> drivers/net/wireless/intel/iwlwifi/mvm/d3.c:2982:58: warning: operation on 'net_detect->n_matches' may be undefined [-Wsequence-point]
>   2982 |                 net_detect->matches[net_detect->n_matches++] = match;
>        |                                     ~~~~~~~~~~~~~~~~~~~~~^~
> 

Nice catch! :)

> Fixes: aa4ec06c455d ("wifi: cfg80211: use __counted_by where appropriate")
> Signed-off-by: Kees Cook <kees@kernel.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks
-- 
Gustavo

> ---
> Cc: Miri Korenblit <miriam.rachel.korenblit@intel.com>
> Cc: Kalle Valo <kvalo@kernel.org>
> Cc: Johannes Berg <johannes.berg@intel.com>
> Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
> Cc: Luca Coelho <luciano.coelho@intel.com>
> Cc: Gregory Greenman <gregory.greenman@intel.com>
> Cc: Yedidya Benshimol <yedidya.ben.shimol@intel.com>
> Cc: Haim Dreyfuss <haim.dreyfuss@intel.com>
> Cc: linux-wireless@vger.kernel.org
> ---
>   drivers/net/wireless/intel/iwlwifi/mvm/d3.c | 14 +++++++++++---
>   1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> index 54f4acbbd05b..9cd03ea4680d 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> @@ -2866,6 +2866,7 @@ static void iwl_mvm_query_set_freqs(struct iwl_mvm *mvm,
>   				    int idx)
>   {
>   	int i;
> +	int n_channels = 0;
>   
>   	if (fw_has_api(&mvm->fw->ucode_capa,
>   		       IWL_UCODE_TLV_API_SCAN_OFFLOAD_CHANS)) {
> @@ -2874,7 +2875,7 @@ static void iwl_mvm_query_set_freqs(struct iwl_mvm *mvm,
>   
>   		for (i = 0; i < SCAN_OFFLOAD_MATCHING_CHANNELS_LEN * 8; i++)
>   			if (matches[idx].matching_channels[i / 8] & (BIT(i % 8)))
> -				match->channels[match->n_channels++] =
> +				match->channels[n_channels++] =
>   					mvm->nd_channels[i]->center_freq;
>   	} else {
>   		struct iwl_scan_offload_profile_match_v1 *matches =
> @@ -2882,9 +2883,11 @@ static void iwl_mvm_query_set_freqs(struct iwl_mvm *mvm,
>   
>   		for (i = 0; i < SCAN_OFFLOAD_MATCHING_CHANNELS_LEN_V1 * 8; i++)
>   			if (matches[idx].matching_channels[i / 8] & (BIT(i % 8)))
> -				match->channels[match->n_channels++] =
> +				match->channels[n_channels++] =
>   					mvm->nd_channels[i]->center_freq;
>   	}
> +	/* We may have ended up with fewer channels than we allocated. */
> +	match->n_channels = n_channels;
>   }
>   
>   /**
> @@ -2965,6 +2968,8 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>   			     GFP_KERNEL);
>   	if (!net_detect || !n_matches)
>   		goto out_report_nd;
> +	net_detect->n_matches = n_matches;
> +	n_matches = 0;
>   
>   	for_each_set_bit(i, &matched_profiles, mvm->n_nd_match_sets) {
>   		struct cfg80211_wowlan_nd_match *match;
> @@ -2978,8 +2983,9 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>   				GFP_KERNEL);
>   		if (!match)
>   			goto out_report_nd;
> +		match->n_channels = n_channels;
>   
> -		net_detect->matches[net_detect->n_matches++] = match;
> +		net_detect->matches[n_matches++] = match;
>   
>   		/* We inverted the order of the SSIDs in the scan
>   		 * request, so invert the index here.
> @@ -2994,6 +3000,8 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>   
>   		iwl_mvm_query_set_freqs(mvm, d3_data->nd_results, match, i);
>   	}
> +	/* We may have fewer matches than we allocated. */
> +	net_detect->n_matches = n_matches;
>   
>   out_report_nd:
>   	wakeup.net_detect = net_detect;