wifi: iwlwifi: mvm: Fix __counted_by usage in cfg80211_wowlan_nd_*

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;
      |                                     ~~~~~~~~~~~~~~~~~~~~~^~

Cc: stable@vger.kernel.org
Fixes: aa4ec06 ("wifi: cfg80211: use __counted_by where appropriate")
Signed-off-by: Kees Cook <kees@kernel.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://patch.msgid.link/20240619211233.work.355-kees@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: kees

drivers/net/wireless/intel/iwlwifi/mvm/d3.c

@@ -2954,6 +2954,7 @@ 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)) {
@@ -2962,17 +2963,19 @@ 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 =
 			 (void *)results->matches;
 
 		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;
 }
 
 /**
@@ -3053,6 +3056,8 @@ 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;
@@ -3066,8 +3071,9 @@ 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.
@@ -3082,6 +3088,8 @@ 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;