wifi: iwlwifi: mvm: don't trust firmware n_channels

If the firmware sends us a corrupted MCC response with
n_channels much larger than the command response can be,
we might copy far too much (uninitialized) memory and
even crash if the n_channels is large enough to make it
run out of the one page allocated for the FW response.

Fix that by checking the lengths. Doing a < comparison
would be sufficient, but the firmware should be doing
it correctly, so check more strictly.

Fixes: dcaf9f5e ("iwlwifi: mvm: add MCC update FW API")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230514120631.d7b233139eb4.I51fd319df8e9d41881fc8450e83d78049518a79a@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

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

@@ -445,6 +445,11 @@ iwl_mvm_update_mcc(struct iwl_mvm *mvm, const char *alpha2,
 		struct iwl_mcc_update_resp *mcc_resp = (void *)pkt->data;
 
 		n_channels =  __le32_to_cpu(mcc_resp->n_channels);
+		if (iwl_rx_packet_payload_len(pkt) !=
+		    struct_size(mcc_resp, channels, n_channels)) {
+			resp_cp = ERR_PTR(-EINVAL);
+			goto exit;
+		}
 		resp_len = sizeof(struct iwl_mcc_update_resp) +
 			   n_channels * sizeof(__le32);
 		resp_cp = kmemdup(mcc_resp, resp_len, GFP_KERNEL);
@@ -456,6 +461,11 @@ iwl_mvm_update_mcc(struct iwl_mvm *mvm, const char *alpha2,
 		struct iwl_mcc_update_resp_v3 *mcc_resp_v3 = (void *)pkt->data;
 
 		n_channels =  __le32_to_cpu(mcc_resp_v3->n_channels);
+		if (iwl_rx_packet_payload_len(pkt) !=
+		    struct_size(mcc_resp_v3, channels, n_channels)) {
+			resp_cp = ERR_PTR(-EINVAL);
+			goto exit;
+		}
 		resp_len = sizeof(struct iwl_mcc_update_resp) +
 			   n_channels * sizeof(__le32);
 		resp_cp = kzalloc(resp_len, GFP_KERNEL);