wifi: mac80211: add a workaround for receiving non-standard mesh A-MSDU

At least ath10k and ath11k supported hardware (maybe more) does not implement
mesh A-MSDU aggregation in a standard compliant way.
802.11-2020 9.3.2.2.2 declares that the Mesh Control field is part of the
A-MSDU header (and little-endian).
As such, its length must not be included in the subframe length field.
Hardware affected by this bug treats the mesh control field as part of the
MSDU data and sets the length accordingly.
In order to avoid packet loss, keep track of which stations are affected
by this and take it into account when converting A-MSDU to 802.3 + mesh control
packets.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20230213100855.34315-5-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -6236,6 +6236,19 @@ static inline int ieee80211_data_to_8023(struct sk_buff *skb, const u8 *addr,
 	return ieee80211_data_to_8023_exthdr(skb, NULL, addr, iftype, 0, false);
 }
 
+/**
+ * ieee80211_is_valid_amsdu - check if subframe lengths of an A-MSDU are valid
+ *
+ * This is used to detect non-standard A-MSDU frames, e.g. the ones generated
+ * by ath10k and ath11k, where the subframe length includes the length of the
+ * mesh control field.
+ *
+ * @skb: The input A-MSDU frame without any headers.
+ * @mesh_hdr: use standard compliant mesh A-MSDU subframe header
+ * Returns: true if subframe header lengths are valid for the @mesh_hdr mode
+ */
+bool ieee80211_is_valid_amsdu(struct sk_buff *skb, bool mesh_hdr);
+
 /**
  * ieee80211_amsdu_to_8023s - decode an IEEE 802.11n A-MSDU frame
  *

net/mac80211/rx.c

@@ -2899,7 +2899,6 @@ __ieee80211_rx_h_amsdu(struct ieee80211_rx_data *rx, u8 data_offset)
 	static ieee80211_rx_result res;
 	struct ethhdr ethhdr;
 	const u8 *check_da = ethhdr.h_dest, *check_sa = ethhdr.h_source;
-	bool mesh = false;
 
 	if (unlikely(ieee80211_has_a4(hdr->frame_control))) {
 		check_da = NULL;
@@ -2917,7 +2916,6 @@ __ieee80211_rx_h_amsdu(struct ieee80211_rx_data *rx, u8 data_offset)
 		case NL80211_IFTYPE_MESH_POINT:
 			check_sa = NULL;
 			check_da = NULL;
-			mesh = true;
 			break;
 		default:
 			break;
@@ -2932,10 +2930,21 @@ __ieee80211_rx_h_amsdu(struct ieee80211_rx_data *rx, u8 data_offset)
 					  data_offset, true))
 		return RX_DROP_UNUSABLE;
 
+	if (rx->sta && rx->sta->amsdu_mesh_control < 0) {
+		bool valid_std = ieee80211_is_valid_amsdu(skb, true);
+		bool valid_nonstd = ieee80211_is_valid_amsdu(skb, false);
+
+		if (valid_std && !valid_nonstd)
+			rx->sta->amsdu_mesh_control = 1;
+		else if (valid_nonstd && !valid_std)
+			rx->sta->amsdu_mesh_control = 0;
+	}
+
 	ieee80211_amsdu_to_8023s(skb, &frame_list, dev->dev_addr,
 				 rx->sdata->vif.type,
 				 rx->local->hw.extra_tx_headroom,
-				 check_da, check_sa, mesh);
+				 check_da, check_sa,
+				 rx->sta->amsdu_mesh_control);
 
 	while (!skb_queue_empty(&frame_list)) {
 		rx->skb = __skb_dequeue(&frame_list);

net/mac80211/sta_info.c

@@ -594,6 +594,9 @@ __sta_info_alloc(struct ieee80211_sub_if_data *sdata,
 
 	sta->sta_state = IEEE80211_STA_NONE;
 
+	if (sdata->vif.type == NL80211_IFTYPE_MESH_POINT)
+		sta->amsdu_mesh_control = -1;
+
 	/* Mark TID as unreserved */
 	sta->reserved_tid = IEEE80211_TID_UNRESERVED;
 

net/mac80211/sta_info.h

@@ -707,6 +707,7 @@ struct sta_info {
 	struct codel_params cparams;
 
 	u8 reserved_tid;
+	s8 amsdu_mesh_control;
 
 	struct cfg80211_chan_def tdls_chandef;
 

net/wireless/util.c

@@ -776,6 +776,38 @@ __ieee80211_amsdu_copy(struct sk_buff *skb, unsigned int hlen,
 	return frame;
 }
 
+bool ieee80211_is_valid_amsdu(struct sk_buff *skb, bool mesh_hdr)
+{
+	int offset = 0, remaining, subframe_len, padding;
+
+	for (offset = 0; offset < skb->len; offset += subframe_len + padding) {
+		struct {
+		    __be16 len;
+		    u8 mesh_flags;
+		} hdr;
+		u16 len;
+
+		if (skb_copy_bits(skb, offset + 2 * ETH_ALEN, &hdr, sizeof(hdr)) < 0)
+			return false;
+
+		if (mesh_hdr)
+			len = le16_to_cpu(*(__le16 *)&hdr.len) +
+			      __ieee80211_get_mesh_hdrlen(hdr.mesh_flags);
+		else
+			len = ntohs(hdr.len);
+
+		subframe_len = sizeof(struct ethhdr) + len;
+		padding = (4 - subframe_len) & 0x3;
+		remaining = skb->len - offset;
+
+		if (subframe_len > remaining)
+			return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(ieee80211_is_valid_amsdu);
+
 void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
 			      const u8 *addr, enum nl80211_iftype iftype,
 			      const unsigned int extra_headroom,