wifi: mac80211: fix receiving A-MSDU frames on mesh interfaces

The current mac80211 mesh A-MSDU receive path fails to parse A-MSDU packets
on mesh interfaces, because it assumes that the Mesh Control field is always
directly after the 802.11 header.
802.11-2020 9.3.2.2.2 Figure 9-70 shows that the Mesh Control field is
actually part of the A-MSDU subframe header.
This makes more sense, since it allows packets for multiple different
destinations to be included in the same A-MSDU, as long as RA and TID are
still the same.
Another issue is the fact that the A-MSDU subframe length field was apparently
accidentally defined as little-endian in the standard.

In order to fix this, the mesh forwarding path needs happen at a different
point in the receive path.

ieee80211_data_to_8023_exthdr is changed to ignore the mesh control field
and leave it in after the ethernet header. This also affects the source/dest
MAC address fields, which now in the case of mesh point to the mesh SA/DA.

ieee80211_amsdu_to_8023s is changed to deal with the endian difference and
to add the Mesh Control length to the subframe length, since it's not covered
by the MSDU length field.

With these changes, the mac80211 will get the same packet structure for
converted regular data packets and unpacked A-MSDU subframes.

The mesh forwarding checks are now only performed after the A-MSDU decap.
For locally received packets, the Mesh Control header is stripped away.
For forwarded packets, a new 802.11 header gets added.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20230213100855.34315-4-nbd@nbd.name
[fix fortify build error]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 76 insertions, 44 deletions

diff --git a/net/wireless/util.c b/net/wireless/util.c
index 4498807b8b70..8ae117cfc22c 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -542,7 +542,7 @@ unsigned int ieee80211_get_mesh_hdrlen(struct ieee80211s_hdr *meshhdr)
 }
 EXPORT_SYMBOL(ieee80211_get_mesh_hdrlen);
 
-static bool ieee80211_get_8023_tunnel_proto(const void *hdr, __be16 *proto)
+bool ieee80211_get_8023_tunnel_proto(const void *hdr, __be16 *proto)
 {
 	const __be16 *hdr_proto = hdr + ETH_ALEN;
 
@@ -556,6 +556,49 @@ static bool ieee80211_get_8023_tunnel_proto(const void *hdr, __be16 *proto)
 
 	return true;
 }
+EXPORT_SYMBOL(ieee80211_get_8023_tunnel_proto);
+
+int ieee80211_strip_8023_mesh_hdr(struct sk_buff *skb)
+{
+	const void *mesh_addr;
+	struct {
+		struct ethhdr eth;
+		u8 flags;
+	} payload;
+	int hdrlen;
+	int ret;
+
+	ret = skb_copy_bits(skb, 0, &payload, sizeof(payload));
+	if (ret)
+		return ret;
+
+	hdrlen = sizeof(payload.eth) + __ieee80211_get_mesh_hdrlen(payload.flags);
+
+	if (likely(pskb_may_pull(skb, hdrlen + 8) &&
+		   ieee80211_get_8023_tunnel_proto(skb->data + hdrlen,
+						   &payload.eth.h_proto)))
+		hdrlen += ETH_ALEN + 2;
+	else if (!pskb_may_pull(skb, hdrlen))
+		return -EINVAL;
+
+	mesh_addr = skb->data + sizeof(payload.eth) + ETH_ALEN;
+	switch (payload.flags & MESH_FLAGS_AE) {
+	case MESH_FLAGS_AE_A4:
+		memcpy(&payload.eth.h_source, mesh_addr, ETH_ALEN);
+		break;
+	case MESH_FLAGS_AE_A5_A6:
+		memcpy(&payload.eth, mesh_addr, 2 * ETH_ALEN);
+		break;
+	default:
+		break;
+	}
+
+	pskb_pull(skb, hdrlen - sizeof(payload.eth));
+	memcpy(skb->data, &payload.eth, sizeof(payload.eth));
+
+	return 0;
+}
+EXPORT_SYMBOL(ieee80211_strip_8023_mesh_hdr);
 
 int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 				  const u8 *addr, enum nl80211_iftype iftype,
@@ -568,7 +611,6 @@ int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 	} payload;
 	struct ethhdr tmp;
 	u16 hdrlen;
-	u8 mesh_flags = 0;
 
 	if (unlikely(!ieee80211_is_data_present(hdr->frame_control)))
 		return -1;
@@ -589,12 +631,6 @@ int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 	memcpy(tmp.h_dest, ieee80211_get_DA(hdr), ETH_ALEN);
 	memcpy(tmp.h_source, ieee80211_get_SA(hdr), ETH_ALEN);
 
-	if (iftype == NL80211_IFTYPE_MESH_POINT &&
-	    skb_copy_bits(skb, hdrlen, &mesh_flags, 1) < 0)
-		return -1;
-
-	mesh_flags &= MESH_FLAGS_AE;
-
 	switch (hdr->frame_control &
 		cpu_to_le16(IEEE80211_FCTL_TODS | IEEE80211_FCTL_FROMDS)) {
 	case cpu_to_le16(IEEE80211_FCTL_TODS):
@@ -608,17 +644,6 @@ int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 			     iftype != NL80211_IFTYPE_AP_VLAN &&
 			     iftype != NL80211_IFTYPE_STATION))
 			return -1;
-		if (iftype == NL80211_IFTYPE_MESH_POINT) {
-			if (mesh_flags == MESH_FLAGS_AE_A4)
-				return -1;
-			if (mesh_flags == MESH_FLAGS_AE_A5_A6 &&
-			    skb_copy_bits(skb, hdrlen +
-					  offsetof(struct ieee80211s_hdr, eaddr1),
-					  tmp.h_dest, 2 * ETH_ALEN) < 0)
-				return -1;
-
-			hdrlen += __ieee80211_get_mesh_hdrlen(mesh_flags);
-		}
 		break;
 	case cpu_to_le16(IEEE80211_FCTL_FROMDS):
 		if ((iftype != NL80211_IFTYPE_STATION &&
@@ -627,16 +652,6 @@ int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 		    (is_multicast_ether_addr(tmp.h_dest) &&
 		     ether_addr_equal(tmp.h_source, addr)))
 			return -1;
-		if (iftype == NL80211_IFTYPE_MESH_POINT) {
-			if (mesh_flags == MESH_FLAGS_AE_A5_A6)
-				return -1;
-			if (mesh_flags == MESH_FLAGS_AE_A4 &&
-			    skb_copy_bits(skb, hdrlen +
-					  offsetof(struct ieee80211s_hdr, eaddr1),
-					  tmp.h_source, ETH_ALEN) < 0)
-				return -1;
-			hdrlen += __ieee80211_get_mesh_hdrlen(mesh_flags);
-		}
 		break;
 	case cpu_to_le16(0):
 		if (iftype != NL80211_IFTYPE_ADHOC &&
@@ -646,7 +661,7 @@ int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 		break;
 	}
 
-	if (likely(!is_amsdu &&
+	if (likely(!is_amsdu && iftype != NL80211_IFTYPE_MESH_POINT &&
 		   skb_copy_bits(skb, hdrlen, &payload, sizeof(payload)) == 0 &&
 		   ieee80211_get_8023_tunnel_proto(&payload, &tmp.h_proto))) {
 		/* remove RFC1042 or Bridge-Tunnel encapsulation */
@@ -722,7 +737,8 @@ __ieee80211_amsdu_copy_frag(struct sk_buff *skb, struct sk_buff *frame,
 
 static struct sk_buff *
 __ieee80211_amsdu_copy(struct sk_buff *skb, unsigned int hlen,
-		       int offset, int len, bool reuse_frag)
+		       int offset, int len, bool reuse_frag,
+		       int min_len)
 {
 	struct sk_buff *frame;
 	int cur_len = len;
@@ -736,7 +752,7 @@ __ieee80211_amsdu_copy(struct sk_buff *skb, unsigned int hlen,
 	 * in the stack later.
 	 */
 	if (reuse_frag)
-		cur_len = min_t(int, len, 32);
+		cur_len = min_t(int, len, min_len);
 
 	/*
 	 * Allocate and reserve two bytes more for payload
@@ -746,6 +762,7 @@ __ieee80211_amsdu_copy(struct sk_buff *skb, unsigned int hlen,
 	if (!frame)
 		return NULL;
 
+	frame->priority = skb->priority;
 	skb_reserve(frame, hlen + sizeof(struct ethhdr) + 2);
 	skb_copy_bits(skb, offset, skb_put(frame, cur_len), cur_len);
 
@@ -762,23 +779,37 @@ __ieee80211_amsdu_copy(struct sk_buff *skb, unsigned int hlen,
 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,
-			      const u8 *check_da, const u8 *check_sa)
+			      const u8 *check_da, const u8 *check_sa,
+			      bool mesh_control)
 {
 	unsigned int hlen = ALIGN(extra_headroom, 4);
 	struct sk_buff *frame = NULL;
 	int offset = 0, remaining;
-	struct ethhdr eth;
+	struct {
+		struct ethhdr eth;
+		uint8_t flags;
+	} hdr;
 	bool reuse_frag = skb->head_frag && !skb_has_frag_list(skb);
 	bool reuse_skb = false;
 	bool last = false;
+	int copy_len = sizeof(hdr.eth);
+
+	if (iftype == NL80211_IFTYPE_MESH_POINT)
+		copy_len = sizeof(hdr);
 
 	while (!last) {
 		unsigned int subframe_len;
-		int len;
+		int len, mesh_len = 0;
 		u8 padding;
 
-		skb_copy_bits(skb, offset, &eth, sizeof(eth));
-		len = ntohs(eth.h_proto);
+		skb_copy_bits(skb, offset, &hdr, copy_len);
+		if (iftype == NL80211_IFTYPE_MESH_POINT)
+			mesh_len = __ieee80211_get_mesh_hdrlen(hdr.flags);
+		if (mesh_control)
+			len = le16_to_cpu(*(__le16 *)&hdr.eth.h_proto) + mesh_len;
+		else
+			len = ntohs(hdr.eth.h_proto);
+
 		subframe_len = sizeof(struct ethhdr) + len;
 		padding = (4 - subframe_len) & 0x3;
 
@@ -787,16 +818,16 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
 		if (subframe_len > remaining)
 			goto purge;
 		/* mitigate A-MSDU aggregation injection attacks */
-		if (ether_addr_equal(eth.h_dest, rfc1042_header))
+		if (ether_addr_equal(hdr.eth.h_dest, rfc1042_header))
 			goto purge;
 
 		offset += sizeof(struct ethhdr);
 		last = remaining <= subframe_len + padding;
 
 		/* FIXME: should we really accept multicast DA? */
-		if ((check_da && !is_multicast_ether_addr(eth.h_dest) &&
-		     !ether_addr_equal(check_da, eth.h_dest)) ||
-		    (check_sa && !ether_addr_equal(check_sa, eth.h_source))) {
+		if ((check_da && !is_multicast_ether_addr(hdr.eth.h_dest) &&
+		     !ether_addr_equal(check_da, hdr.eth.h_dest)) ||
+		    (check_sa && !ether_addr_equal(check_sa, hdr.eth.h_source))) {
 			offset += len + padding;
 			continue;
 		}
@@ -808,7 +839,7 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
 			reuse_skb = true;
 		} else {
 			frame = __ieee80211_amsdu_copy(skb, hlen, offset, len,
-						       reuse_frag);
+						       reuse_frag, 32 + mesh_len);
 			if (!frame)
 				goto purge;
 
@@ -819,10 +850,11 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
 		frame->dev = skb->dev;
 		frame->priority = skb->priority;
 
-		if (likely(ieee80211_get_8023_tunnel_proto(frame->data, &eth.h_proto)))
+		if (likely(iftype != NL80211_IFTYPE_MESH_POINT &&
+			   ieee80211_get_8023_tunnel_proto(frame->data, &hdr.eth.h_proto)))
 			skb_pull(frame, ETH_ALEN + 2);
 
-		memcpy(skb_push(frame, sizeof(eth)), &eth, sizeof(eth));
+		memcpy(skb_push(frame, sizeof(hdr.eth)), &hdr.eth, sizeof(hdr.eth));
 		__skb_queue_tail(list, frame);
 	}