wifi: iwlwifi: calib: Refactor iwl_calib_result usage for clarity

In preparation for FORTIFY_SOURCE performing run-time destination buffer
bounds checking for memcpy(), refactor the use of struct iwl_calib_result:

- Have struct iwl_calib_result contain struct iwl_calib_cmd since
  functions expect to operate on the "data" flex array in "cmd", which
  follows the "hdr" member.
- Switch argument passing around to use struct iwl_calib_cmd instead of
  struct iwl_calib_hdr to prepare functions to see the "data" member.
- Change iwl_calib_set()'s "len" argument to a size_t since it is always
  unsigned and is normally receiving the output of sizeof().
- Add an explicit length sanity check in iwl_calib_set().
- Adjust the memcpy() to avoid copying across the now visible composite
  flex array structure.

This avoids the future run-time warning:

  memcpy: detected field-spanning write (size 8) of single field "&res->hdr" (size 4)

Cc: Luca Coelho <luciano.coelho@intel.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Reported-by: Andy Lavr <andy.lavr@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220901204558.2256458-1-keescook@chromium.org

drivers/net/wireless/intel/iwlwifi/dvm/agn.h

@@ -112,7 +112,7 @@ int iwl_load_ucode_wait_alive(struct iwl_priv *priv,
 			      enum iwl_ucode_type ucode_type);
 int iwl_send_calib_results(struct iwl_priv *priv);
 int iwl_calib_set(struct iwl_priv *priv,
-		  const struct iwl_calib_hdr *cmd, int len);
+		  const struct iwl_calib_cmd *cmd, size_t len);
 void iwl_calib_free_results(struct iwl_priv *priv);
 int iwl_dump_nic_event_log(struct iwl_priv *priv, bool full_log,
 			    char **buf);

drivers/net/wireless/intel/iwlwifi/dvm/calib.c

@@ -19,8 +19,7 @@
 struct iwl_calib_result {
 	struct list_head list;
 	size_t cmd_len;
-	struct iwl_calib_hdr hdr;
-	/* data follows */
+	struct iwl_calib_cmd cmd;
 };
 
 struct statistics_general_data {
@@ -43,12 +42,12 @@ int iwl_send_calib_results(struct iwl_priv *priv)
 		int ret;
 
 		hcmd.len[0] = res->cmd_len;
-		hcmd.data[0] = &res->hdr;
+		hcmd.data[0] = &res->cmd;
 		hcmd.dataflags[0] = IWL_HCMD_DFL_NOCOPY;
 		ret = iwl_dvm_send_cmd(priv, &hcmd);
 		if (ret) {
 			IWL_ERR(priv, "Error %d on calib cmd %d\n",
-				ret, res->hdr.op_code);
+				ret, res->cmd.hdr.op_code);
 			return ret;
 		}
 	}
@@ -57,19 +56,22 @@ int iwl_send_calib_results(struct iwl_priv *priv)
 }
 
 int iwl_calib_set(struct iwl_priv *priv,
-		  const struct iwl_calib_hdr *cmd, int len)
+		  const struct iwl_calib_cmd *cmd, size_t len)
 {
 	struct iwl_calib_result *res, *tmp;
 
-	res = kmalloc(sizeof(*res) + len - sizeof(struct iwl_calib_hdr),
-		      GFP_ATOMIC);
+	if (check_sub_overflow(len, sizeof(*cmd), &len))
+		return -ENOMEM;
+
+	res = kmalloc(struct_size(res, cmd.data, len), GFP_ATOMIC);
 	if (!res)
 		return -ENOMEM;
-	memcpy(&res->hdr, cmd, len);
-	res->cmd_len = len;
+	res->cmd = *cmd;
+	memcpy(res->cmd.data, cmd->data, len);
+	res->cmd_len = struct_size(cmd, data, len);
 
 	list_for_each_entry(tmp, &priv->calib_results, list) {
-		if (tmp->hdr.op_code == res->hdr.op_code) {
+		if (tmp->cmd.hdr.op_code == res->cmd.hdr.op_code) {
 			list_replace(&tmp->list, &res->list);
 			kfree(tmp);
 			return 0;

drivers/net/wireless/intel/iwlwifi/dvm/ucode.c

@@ -356,18 +356,18 @@ static bool iwlagn_wait_calib(struct iwl_notif_wait_data *notif_wait,
 			      struct iwl_rx_packet *pkt, void *data)
 {
 	struct iwl_priv *priv = data;
-	struct iwl_calib_hdr *hdr;
+	struct iwl_calib_cmd *cmd;
 
 	if (pkt->hdr.cmd != CALIBRATION_RES_NOTIFICATION) {
 		WARN_ON(pkt->hdr.cmd != CALIBRATION_COMPLETE_NOTIFICATION);
 		return true;
 	}
 
-	hdr = (struct iwl_calib_hdr *)pkt->data;
+	cmd = (struct iwl_calib_cmd *)pkt->data;
 
-	if (iwl_calib_set(priv, hdr, iwl_rx_packet_payload_len(pkt)))
+	if (iwl_calib_set(priv, cmd, iwl_rx_packet_payload_len(pkt)))
 		IWL_ERR(priv, "Failed to record calibration data %d\n",
-			hdr->op_code);
+			cmd->hdr.op_code);
 
 	return false;
 }