iwlwifi: mvm: fix deduplication start logic

If the first frame on a given TID is received with seqno 0 and needed
to be retransmitted, we erroneously drop it because the deduplication
data is initialized to zero, and then comparing

        if (unlikely(ieee80211_has_retry(hdr->frame_control) &&
                     dup_data->last_seq[tid] == hdr->seq_ctrl &&
                     dup_data->last_sub_frame[tid] >= sub_frame_idx))
                return true;

will return in iwl_mvm_is_dup() since last_sub_frame is also set to
zero, and sub_frame_idx is usually zero since this only covers the
relatively rare case of A-MSDU.

Fix this by initializing the last_seq array to 0xffff, which is an
impossible value for hdr->seq_ctrl to have here because the lower
four bits are the fragment number, and fragments aren't handled in
this code but go to mac80211 instead.

Fixes: a571f5f635ef ("iwlwifi: mvm: add duplicate packet detection per rx queue")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

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

@@ -1402,11 +1402,24 @@ int iwl_mvm_add_sta(struct iwl_mvm *mvm,
 
 	if (iwl_mvm_has_new_rx_api(mvm) &&
 	    !test_bit(IWL_MVM_STATUS_IN_HW_RESTART, &mvm->status)) {
+		int q;
+
 		dup_data = kcalloc(mvm->trans->num_rx_queues,
-				   sizeof(*dup_data),
-				   GFP_KERNEL);
+				   sizeof(*dup_data), GFP_KERNEL);
 		if (!dup_data)
 			return -ENOMEM;
+		/*
+		 * Initialize all the last_seq values to 0xffff which can never
+		 * compare equal to the frame's seq_ctrl in the check in
+		 * iwl_mvm_is_dup() since the lower 4 bits are the fragment
+		 * number and fragmented packets don't reach that function.
+		 *
+		 * This thus allows receiving a packet with seqno 0 and the
+		 * retry bit set as the very first packet on a new TID.
+		 */
+		for (q = 0; q < mvm->trans->num_rx_queues; q++)
+			memset(dup_data[q].last_seq, 0xff,
+			       sizeof(dup_data[q].last_seq));
 		mvm_sta->dup_data = dup_data;
 	}