[PATCH mt76 15/15] wifi: mt76: mt7925: fix infinite loop in UNI event TLV parsing

[Felix Fietkau <nbd@nbd.name>]

The event TLV loops accept a zero-length TLV, which advances neither the
cursor nor the remaining length, so a malformed event hangs the caller.
mt7925_mcu_uni_roc_event() additionally walked past the end of the skb,
since it never checked the declared length against the remainder.

Replace the five open-coded loops with a shared iterator that rejects
lengths below the TLV header and beyond the remaining buffer, and check
the per-tag payload sizes before dereferencing them.

While here, make the RSSI monitor event read from the current TLV rather
than from the start of the list.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 .../net/wireless/mediatek/mt76/mt7925/main.c  | 10 ++---
 .../net/wireless/mediatek/mt76/mt7925/mcu.c   | 38 +++++++++++--------
 .../net/wireless/mediatek/mt76/mt7925/mcu.h   | 19 ++++++++++
 3 files changed, 46 insertions(+), 21 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/main.c b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
index 8586e18c2fa3..825cdced9f40 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
@@ -1562,7 +1562,7 @@ void mt7925_scan_work(struct work_struct *work)
 	while (true) {
 		struct sk_buff *skb;
 		struct tlv *tlv;
-		int tlv_len;
+		u32 tlv_len;
 
 		spin_lock_bh(&phy->dev->mt76.lock);
 		skb = __skb_dequeue(&phy->scan_event_list);
@@ -1575,7 +1575,7 @@ void mt7925_scan_work(struct work_struct *work)
 		tlv = (struct tlv *)skb->data;
 		tlv_len = skb->len;
 
-		while (tlv_len > 0 && le16_to_cpu(tlv->len) <= tlv_len) {
+		mt7925_for_each_tlv(tlv, tlv_len) {
 			struct mt7925_mcu_scan_chinfo_event *evt;
 
 			switch (le16_to_cpu(tlv->tag)) {
@@ -1588,6 +1588,9 @@ void mt7925_scan_work(struct work_struct *work)
 				}
 				break;
 			case UNI_EVENT_SCAN_DONE_CHNLINFO:
+				if (le16_to_cpu(tlv->len) < sizeof(*tlv) + sizeof(*evt))
+					break;
+
 				evt = (struct mt7925_mcu_scan_chinfo_event *)tlv->data;
 
 				mt7925_regd_change(phy, evt->alpha2);
@@ -1599,9 +1602,6 @@ void mt7925_scan_work(struct work_struct *work)
 			default:
 				break;
 			}
-
-			tlv_len -= le16_to_cpu(tlv->len);
-			tlv = (struct tlv *)((char *)(tlv) + le16_to_cpu(tlv->len));
 		}
 
 		dev_kfree_skb(skb);
diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c b/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c
index 8ca4c952d399..1219a370300a 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c
@@ -409,16 +409,18 @@ mt7925_mcu_uni_hif_ctrl_event(struct mt792x_dev *dev, struct sk_buff *skb)
 	tlv = (struct tlv *)skb->data;
 	tlv_len = skb->len;
 
-	while (tlv_len > 0 && le16_to_cpu(tlv->len) <= tlv_len) {
+	mt7925_for_each_tlv(tlv, tlv_len) {
 		switch (le16_to_cpu(tlv->tag)) {
 		case UNI_EVENT_HIF_CTRL_BASIC:
+			if (le16_to_cpu(tlv->len) <
+			    sizeof(struct mt7925_mcu_hif_ctrl_basic_tlv))
+				break;
+
 			mt7925_mcu_handle_hif_ctrl_basic(dev, tlv);
 			break;
 		default:
 			break;
 		}
-		tlv_len -= le16_to_cpu(tlv->len);
-		tlv = (struct tlv *)((char *)(tlv) + le16_to_cpu(tlv->len));
 	}
 }
 
@@ -426,22 +428,24 @@ static void
 mt7925_mcu_uni_roc_event(struct mt792x_dev *dev, struct sk_buff *skb)
 {
 	struct tlv *tlv;
-	int i = 0;
+	u32 tlv_len;
 
 	skb_pull(skb, sizeof(struct mt7925_mcu_rxd) + 4);
+	tlv = (struct tlv *)skb->data;
+	tlv_len = skb->len;
 
-	while (i < skb->len) {
-		tlv = (struct tlv *)(skb->data + i);
-
+	mt7925_for_each_tlv(tlv, tlv_len) {
 		switch (le16_to_cpu(tlv->tag)) {
 		case UNI_EVENT_ROC_GRANT:
+			if (le16_to_cpu(tlv->len) <
+			    sizeof(struct mt7925_roc_grant_tlv))
+				break;
+
 			mt7925_mcu_roc_handle_grant(dev, tlv);
 			break;
 		case UNI_EVENT_ROC_GRANT_SUB_LINK:
 			break;
 		}
-
-		i += le16_to_cpu(tlv->len);
 	}
 }
 
@@ -476,7 +480,7 @@ mt7925_mcu_tx_done_event(struct mt792x_dev *dev, struct sk_buff *skb)
 	tlv = (struct tlv *)skb->data;
 	tlv_len = skb->len;
 
-	while (tlv_len > 0 && le16_to_cpu(tlv->len) <= tlv_len) {
+	mt7925_for_each_tlv(tlv, tlv_len) {
 		switch (le16_to_cpu(tlv->tag)) {
 		case UNI_EVENT_TX_DONE_MSG:
 			struct mt7928_uni_txdone_event *evt;
@@ -484,6 +488,9 @@ mt7925_mcu_tx_done_event(struct mt792x_dev *dev, struct sk_buff *skb)
 			if (!is_mt7928(&dev->mt76))
 				break;
 
+			if (le16_to_cpu(tlv->len) < sizeof(*evt))
+				break;
+
 			evt = (struct mt7928_uni_txdone_event *)tlv;
 			if (evt->status) {
 				dev_info(dev->mt76.dev,
@@ -510,8 +517,6 @@ mt7925_mcu_tx_done_event(struct mt792x_dev *dev, struct sk_buff *skb)
 		default:
 			break;
 		}
-		tlv_len -= le16_to_cpu(tlv->len);
-		tlv = (struct tlv *)((char *)(tlv) + le16_to_cpu(tlv->len));
 	}
 }
 
@@ -548,10 +553,13 @@ mt7925_mcu_rssi_monitor_event(struct mt792x_dev *dev, struct sk_buff *skb)
 	tlv = (struct tlv *)skb->data;
 	tlv_len = skb->len;
 
-	while (tlv_len > 0 && le16_to_cpu(tlv->len) <= tlv_len) {
+	mt7925_for_each_tlv(tlv, tlv_len) {
 		switch (le16_to_cpu(tlv->tag)) {
 		case UNI_EVENT_RSSI_MONITOR_INFO:
-			event = (struct mt7925_uni_rssi_monitor_event *)skb->data;
+			if (le16_to_cpu(tlv->len) < sizeof(*event))
+				break;
+
+			event = (struct mt7925_uni_rssi_monitor_event *)tlv;
 			ieee80211_iterate_active_interfaces_atomic(dev->mt76.hw,
 								   IEEE80211_IFACE_ITER_RESUME_ALL,
 								   mt7925_mcu_rssi_monitor_iter,
@@ -560,8 +568,6 @@ mt7925_mcu_rssi_monitor_event(struct mt792x_dev *dev, struct sk_buff *skb)
 		default:
 			break;
 		}
-		tlv_len -= le16_to_cpu(tlv->len);
-		tlv = (struct tlv *)((char *)(tlv) + le16_to_cpu(tlv->len));
 	}
 }
 
diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mcu.h b/drivers/net/wireless/mediatek/mt76/mt7925/mcu.h
index 154f792a56bc..11f9eac13ffc 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/mcu.h
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/mcu.h
@@ -699,6 +699,25 @@ mt7925_mcu_get_cipher(int cipher)
 	}
 }
 
+static inline bool
+mt7925_mcu_tlv_valid(struct tlv *tlv, u32 rem)
+{
+	u16 len;
+
+	if (rem < sizeof(*tlv))
+		return false;
+
+	len = le16_to_cpu(tlv->len);
+
+	/* a length below the header size would not advance the cursor */
+	return len >= sizeof(*tlv) && len <= rem;
+}
+
+#define mt7925_for_each_tlv(tlv, rem)					\
+	for (; mt7925_mcu_tlv_valid(tlv, rem);				\
+	     (rem) -= le16_to_cpu((tlv)->len),				\
+	     (tlv) = (struct tlv *)((u8 *)(tlv) + le16_to_cpu((tlv)->len)))
+
 int mt7925_mcu_set_dbdc(struct mt76_phy *phy, bool enable);
 int mt7925_mcu_hw_scan(struct mt76_phy *phy, struct ieee80211_vif *vif,
 		       struct ieee80211_scan_request *scan_req);
-- 
2.53.0