Subject: [PATCH] wifi: cfg80211: fix ieee80211_data_to_8023_exthdr handling of small packets
From: Felix Fietkau <[email-masked]>
Date: Fri, 7 Oct 2022 10:54:47 +0200

STP topology change notification packets only have a payload of 7 bytes,
so they get dropped due to the skb->len < hdrlen + 8 check.
Fix this by removing skb->len based checks and instead check the return code
on the skb_copy_bits calls.

Fixes: 2d1c304cb2d5 ("cfg80211: add function for 802.3 conversion with separate output buffer")
Reported-by: Chad Monroe <[email-masked]>
Signed-off-by: Felix Fietkau <[email-masked]>
---

--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -557,7 +557,7 @@ int ieee80211_data_to_8023_exthdr(struct
 		return -1;
 
 	hdrlen = ieee80211_hdrlen(hdr->frame_control) + data_offset;
-	if (skb->len < hdrlen + 8)
+	if (skb->len < hdrlen)
 		return -1;
 
 	/* convert IEEE 802.11 header + possible LLC headers into Ethernet
@@ -572,8 +572,9 @@ int ieee80211_data_to_8023_exthdr(struct
 	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);
+	if (iftype == NL80211_IFTYPE_MESH_POINT &&
+	    skb_copy_bits(skb, hdrlen, &mesh_flags, 1) < 0)
+		return -1;
 
 	mesh_flags &= MESH_FLAGS_AE;
 
@@ -593,11 +594,12 @@ int ieee80211_data_to_8023_exthdr(struct
 		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);
-			}
+			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;
@@ -611,10 +613,11 @@ int ieee80211_data_to_8023_exthdr(struct
 		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);
+			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;
@@ -626,18 +629,18 @@ int ieee80211_data_to_8023_exthdr(struct
 		break;
 	}
 
-	skb_copy_bits(skb, hdrlen, &payload, sizeof(payload));
-	tmp.h_proto = payload.proto;
-
-	if (likely((!is_amsdu && ether_addr_equal(payload.hdr, rfc1042_header) &&
-		    tmp.h_proto != htons(ETH_P_AARP) &&
-		    tmp.h_proto != htons(ETH_P_IPX)) ||
-		   ether_addr_equal(payload.hdr, bridge_tunnel_header)))
+	if (likely(skb_copy_bits(skb, hdrlen, &payload, sizeof(payload)) == 0 &&
+	           ((!is_amsdu && ether_addr_equal(payload.hdr, rfc1042_header) &&
+		     payload.proto != htons(ETH_P_AARP) &&
+		     payload.proto != htons(ETH_P_IPX)) ||
+		    ether_addr_equal(payload.hdr, bridge_tunnel_header)))) {
 		/* remove RFC1042 or Bridge-Tunnel encapsulation and
 		 * replace EtherType */
 		hdrlen += ETH_ALEN + 2;
-	else
+		tmp.h_proto = payload.proto;
+	} else {
 		tmp.h_proto = htons(skb->len - hdrlen);
+	}
 
 	pskb_pull(skb, hdrlen);