wifi: iwlwifi: mvm: add a NULL pointer check

We've observed that in some botched firmware restart scenarios
when the firmware crashes again while we're reconfiguring, we
can hit NULL pointer crashes here. The underlying issue is the
botched restart which we need to fix separately, but until we
can do that, don't crash hard here.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230614123446.e47b0192c78f.I67fa9f07cd1c8b3bdc8db25f5e31c1c680c49745@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c

 // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
 /*
- * Copyright (C) 2012-2014, 2018-2022 Intel Corporation
+ * Copyright (C) 2012-2014, 2018-2023 Intel Corporation
  * Copyright (C) 2013-2014 Intel Mobile Communications GmbH
  * Copyright (C) 2015-2017 Intel Deutschland GmbH
  */
@@ -1111,6 +1111,10 @@ static int iwl_mvm_mac_ctxt_send_beacon_v9(struct iwl_mvm *mvm,
 
 	beacon_cmd.flags = cpu_to_le16(flags);
 	beacon_cmd.byte_cnt = cpu_to_le16((u16)beacon->len);
+
+	if (WARN_ON(!mvmvif->link[link_conf->link_id]))
+		return -EINVAL;
+
 	if (iwl_fw_lookup_cmd_ver(mvm->fw, BEACON_TEMPLATE_CMD, 0) > 12)
 		beacon_cmd.link_id =
 			cpu_to_le32(mvmvif->link[link_conf->link_id]->fw_link_id);

drivers/net/wireless/intel/iwlwifi/mvm/mld-sta.c

 // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
 /*
- * Copyright (C) 2022 Intel Corporation
+ * Copyright (C) 2022-2023 Intel Corporation
  */
 #include "mvm.h"
 #include "time-sync.h"
@@ -369,6 +369,9 @@ int iwl_mvm_mld_rm_bcast_sta(struct iwl_mvm *mvm, struct ieee80211_vif *vif,
 
 	lockdep_assert_held(&mvm->mutex);
 
+	if (WARN_ON(!link))
+		return -EIO;
+
 	switch (vif->type) {
 	case NL80211_IFTYPE_AP:
 	case NL80211_IFTYPE_ADHOC:
@@ -398,6 +401,9 @@ int iwl_mvm_mld_rm_mcast_sta(struct iwl_mvm *mvm, struct ieee80211_vif *vif,
 
 	lockdep_assert_held(&mvm->mutex);
 
+	if (WARN_ON(!link))
+		return -EIO;
+
 	return iwl_mvm_mld_rm_int_sta(mvm, &link->mcast_sta, true, 0,
 				      &link->cab_queue);
 }