wifi: iwlwifi: dvm: Fix memcpy: detected field-spanning write backtrace

A received TKIP key may be up to 32 bytes because it may contain
MIC rx/tx keys too. These are not used by iwl and copying these
over overflows the iwl_keyinfo.key field.

Add a check to not copy more data to iwl_keyinfo.key then will fit.

This fixes backtraces like this one:

 memcpy: detected field-spanning write (size 32) of single field "sta_cmd.key.key" at drivers/net/wireless/intel/iwlwifi/dvm/sta.c:1103 (size 16)
 WARNING: CPU: 1 PID: 946 at drivers/net/wireless/intel/iwlwifi/dvm/sta.c:1103 iwlagn_send_sta_key+0x375/0x390 [iwldvm]
 <snip>
 Hardware name: Dell Inc. Latitude E6430/0H3MT5, BIOS A21 05/08/2017
 RIP: 0010:iwlagn_send_sta_key+0x375/0x390 [iwldvm]
 <snip>
 Call Trace:
  <TASK>
  iwl_set_dynamic_key+0x1f0/0x220 [iwldvm]
  iwlagn_mac_set_key+0x1e4/0x280 [iwldvm]
  drv_set_key+0xa4/0x1b0 [mac80211]
  ieee80211_key_enable_hw_accel+0xa8/0x2d0 [mac80211]
  ieee80211_key_replace+0x22d/0x8e0 [mac80211]
 <snip>

Link: https://www.alionet.org/index.php?topic=1469.0
Link: https://lore.kernel.org/linux-wireless/20230218191056.never.374-kees@kernel.org/
Link: https://lore.kernel.org/linux-wireless/68760035-7f75-1b23-e355-bfb758a87d83@redhat.com/
Cc: Kees Cook <keescook@chromium.org>
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

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

@@ -1081,6 +1081,7 @@ static int iwlagn_send_sta_key(struct iwl_priv *priv,
 {
 	__le16 key_flags;
 	struct iwl_addsta_cmd sta_cmd;
+	size_t to_copy;
 	int i;
 
 	spin_lock_bh(&priv->sta_lock);
@@ -1100,7 +1101,9 @@ static int iwlagn_send_sta_key(struct iwl_priv *priv,
 		sta_cmd.key.tkip_rx_tsc_byte2 = tkip_iv32;
 		for (i = 0; i < 5; i++)
 			sta_cmd.key.tkip_rx_ttak[i] = cpu_to_le16(tkip_p1k[i]);
-		memcpy(sta_cmd.key.key, keyconf->key, keyconf->keylen);
+		/* keyconf may contain MIC rx/tx keys which iwl does not use */
+		to_copy = min_t(size_t, sizeof(sta_cmd.key.key), keyconf->keylen);
+		memcpy(sta_cmd.key.key, keyconf->key, to_copy);
 		break;
 	case WLAN_CIPHER_SUITE_WEP104:
 		key_flags |= STA_KEY_FLG_KEY_SIZE_MSK;