wifi: iwlwifi: mvm/fw: Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are getting ready to enable it, globally.

So, in order to avoid ending up with a flexible-array member in the middle of multiple other structs, we use the __struct_group() helper to create a new tagged struct iwl_tx_cmd_v6_hdr. This structure groups together all the members of the flexible struct iwl_tx_cmd_v6 except the flexible array.

As a result, the array is effectively separated from the rest of the members without modifying the memory layout of the flexible structure. We then change the type of the middle struct members currently causing trouble from struct iwl_tx_cmd_v6 to struct iwl_tx_cmd_v6_hdr.

We also want to ensure that when new members need to be added to the flexible structure, they are always included within the newly created tagged struct. For this, we use static_assert(). This ensures that the memory layout for both the flexible structure and the new tagged struct is the same after any changes.

This approach avoids having to implement struct iwl_tx_cmd_v6_hdr as a completely separate structure, thus preventing having to maintain two independent but basically identical structures, closing the door to potential bugs in the future.

We also use container_of() whenever we need to retrieve a pointer to the flexible structure, through which we can access the flexible-array member, if necessary.

Also, as part of the refactoring required to use __struct_group(), remove unused flex array payload.

So, with these changes, fix the following warnings:

drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tdls.h:134:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tdls.h:53:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tx.h:745:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tx.h:764:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tdls.h:134:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tdls.h:53:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tx.h:745:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tx.h:764:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

---
Changes in v3:
- Rebase on top of commit e4248670c0ae ("wifi: iwlwifi: use normal versioning convention for iwl_tx_cmd")

Changes in v2:
- Update changelog text - mention removal of flex array payload. (Kees)
- Fix kernel-doc block. (Johannes).
- Add RB tag.
- Link: https://lore.kernel.org/linux-hardening/aAv7RiLsmXq5d0ge@kspp/

v1:
- Link: https://lore.kernel.org/linux-hardening/Z-9G-GHufhXKeYft@kspp/

 .../net/wireless/intel/iwlwifi/fw/api/tdls.h  |  4 +-
 .../net/wireless/intel/iwlwifi/fw/api/tx.h    | 63 ++++++++++---------
 .../net/wireless/intel/iwlwifi/mvm/mac-ctxt.c |  8 ++-
 drivers/net/wireless/intel/iwlwifi/mvm/tdls.c | 10 +--
 4 files changed, 45 insertions(+), 40 deletions(-)

index 58d5a6ef633e..84cb7faac647 100644
@@ -50,7 +50,7 @@ struct iwl_tdls_channel_switch_timing {
  */
 struct iwl_tdls_channel_switch_frame {
 	__le32 switch_time_offset;
-	struct iwl_tx_cmd_v6 tx_cmd;
+	struct iwl_tx_cmd_v6_hdr tx_cmd;
 	u8 data[IWL_TDLS_CH_SW_FRAME_MAX_SIZE];
 } __packed; /* TDLS_STA_CHANNEL_SWITCH_FRAME_API_S_VER_1 */
 

@@ -131,7 +131,7 @@ struct iwl_tdls_config_cmd {
 	struct iwl_tdls_sta_info sta_info[IWL_TDLS_STA_COUNT];
 
 	__le32 pti_req_data_offset;
-	struct iwl_tx_cmd_v6 pti_req_tx_cmd;
+	struct iwl_tx_cmd_v6_hdr pti_req_tx_cmd;
 	u8 pti_req_template[];
 } __packed; /* TDLS_CONFIG_CMD_API_S_VER_1 */
 

index 9098a36530cc..67139f704e2c 100644
@@ -1039,7 +1039,9 @@ static int iwl_mvm_mac_ctxt_send_beacon_v6(struct iwl_mvm *mvm,
 	struct iwl_mvm_vif *mvmvif = iwl_mvm_vif_from_mac80211(vif);
 	struct iwl_mac_beacon_cmd_v6 beacon_cmd = {};
 
-	iwl_mvm_mac_ctxt_set_tx(mvm, vif, beacon, &beacon_cmd.tx);
+	iwl_mvm_mac_ctxt_set_tx(mvm, vif, beacon,
+				container_of(&beacon_cmd.tx,
+					     struct iwl_tx_cmd_v6, __hdr));
 
 	beacon_cmd.template_id = cpu_to_le32((u32)mvmvif->id);
 

@@ -1059,7 +1061,9 @@ static int iwl_mvm_mac_ctxt_send_beacon_v7(struct iwl_mvm *mvm,
 	struct iwl_mvm_vif *mvmvif = iwl_mvm_vif_from_mac80211(vif);
 	struct iwl_mac_beacon_cmd_v7 beacon_cmd = {};
 
-	iwl_mvm_mac_ctxt_set_tx(mvm, vif, beacon, &beacon_cmd.tx);
+	iwl_mvm_mac_ctxt_set_tx(mvm, vif, beacon,
+				container_of(&beacon_cmd.tx,
+					     struct iwl_tx_cmd_v6, __hdr));
 
 	beacon_cmd.template_id = cpu_to_le32((u32)mvmvif->id);
 

index 36379b738de1..d475a2fb9c59 100644
@@ -342,6 +342,8 @@ iwl_mvm_tdls_config_channel_switch(struct iwl_mvm *mvm,
 	struct iwl_tdls_channel_switch_cmd_tail *tail =
 		iwl_mvm_chan_info_cmd_tail(mvm, &cmd.ci);
 	u16 len = sizeof(cmd) - iwl_mvm_chan_info_padding(mvm);
+	struct iwl_tx_cmd_v6 *tx_cmd =
+		container_of(&tail->frame.tx_cmd, struct iwl_tx_cmd_v6, __hdr);
 	int ret;
 
 	lockdep_assert_held(&mvm->mutex);

@@ -410,14 +412,12 @@ iwl_mvm_tdls_config_channel_switch(struct iwl_mvm *mvm,
 			ret = -EINVAL;
 			goto out;
 		}
-		iwl_mvm_set_tx_cmd_ccmp(info, &tail->frame.tx_cmd);
+		iwl_mvm_set_tx_cmd_ccmp(info, tx_cmd);
 	}
 
-	iwl_mvm_set_tx_cmd(mvm, skb, &tail->frame.tx_cmd, info,
-			   mvmsta->deflink.sta_id);
+	iwl_mvm_set_tx_cmd(mvm, skb, tx_cmd, info, mvmsta->deflink.sta_id);
 
-	iwl_mvm_set_tx_cmd_rate(mvm, &tail->frame.tx_cmd, info, sta,
-				hdr->frame_control);
+	iwl_mvm_set_tx_cmd_rate(mvm, tx_cmd, info, sta, hdr->frame_control);
 	rcu_read_unlock();
 
 	memcpy(tail->frame.data, skb->data, skb->len);

2.43.0