ath10k: fix handling of wierd MSDU chaining cases

Apparently firmware can sometimes report a
sequence with the first rx descriptor saying it's
not the last MSDU. In that case msdu_chaining
value could be overwritten saying it's not a
chained MSDU. This in turn led to skb_push panic
as the frame could be treated as an A-MSDU instead
of a chained MSDU.

Reported-By: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath10k/htt_rx.c

@@ -312,6 +312,7 @@ static int ath10k_htt_rx_amsdu_pop(struct ath10k_htt *htt,
 	int msdu_len, msdu_chaining = 0;
 	struct sk_buff *msdu;
 	struct htt_rx_desc *rx_desc;
+	bool corrupted = false;
 
 	lockdep_assert_held(&htt->rx_ring.lock);
 
@@ -405,7 +406,6 @@ static int ath10k_htt_rx_amsdu_pop(struct ath10k_htt *htt,
 		msdu_len = MS(__le32_to_cpu(rx_desc->msdu_start.info0),
 			      RX_MSDU_START_INFO0_MSDU_LENGTH);
 		msdu_chained = rx_desc->frag_info.ring2_more_count;
-		msdu_chaining = msdu_chained;
 
 		if (msdu_len_invalid)
 			msdu_len = 0;
@@ -433,11 +433,15 @@ static int ath10k_htt_rx_amsdu_pop(struct ath10k_htt *htt,
 
 			msdu->next = next;
 			msdu = next;
+			msdu_chaining = 1;
 		}
 
 		last_msdu = __le32_to_cpu(rx_desc->msdu_end.info0) &
 				RX_MSDU_END_INFO0_LAST_MSDU;
 
+		if (msdu_chaining && !last_msdu)
+			corrupted = true;
+
 		if (last_msdu) {
 			msdu->next = NULL;
 			break;
@@ -452,6 +456,20 @@ static int ath10k_htt_rx_amsdu_pop(struct ath10k_htt *htt,
 	if (*head_msdu == NULL)
 		msdu_chaining = -1;
 
+	/*
+	 * Apparently FW sometimes reports weird chained MSDU sequences with
+	 * more than one rx descriptor. This seems like a bug but needs more
+	 * analyzing. For the time being fix it by dropping such sequences to
+	 * avoid blowing up the host system.
+	 */
+	if (corrupted) {
+		ath10k_warn("failed to pop chained msdus, dropping\n");
+		ath10k_htt_rx_free_msdu_chain(*head_msdu);
+		*head_msdu = NULL;
+		*tail_msdu = NULL;
+		msdu_chaining = -EINVAL;
+	}
+
 	/*
 	 * Don't refill the ring yet.
 	 *