wifi: mac80211: Use struct instead of macro for PREP frame

The existing PREP_IE_* macros access HWMP PREP frame fields via hardcoded
byte offsets. When the AE (Address Extension) flag is set, an additional
6 bytes appear mid-frame, making the offset arithmetic error-prone.

Introduce typed packed C structs to represent the PREP frame layout:
  - ieee80211_mesh_hwmp_prep_top: fixed fields before the optional AE
    address
  - ieee80211_mesh_hwmp_prep_bottom: fields after the optional AE address

Add ieee80211_mesh_hwmp_prep_get_bottom() to locate the bottom struct
correctly based on whether the AE flag is set.

This preparatory refactoring is needed to fix a 2-byte overread of
orig_addr in hwmp_prep_frame_process() when AE is enabled, which is
addressed in a subsequent patch.

Signed-off-by: Masashi Honma <masashi.honma@gmail.com>
Link: https://patch.msgid.link/20260529230952.124754-2-masashi.honma@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

2 files changed, 49 insertions, 24 deletions

diff --git a/include/linux/ieee80211-mesh.h b/include/linux/ieee80211-mesh.h
index bf4a544aed00..4ce4e47d6d01 100644
--- a/include/linux/ieee80211-mesh.h
+++ b/include/linux/ieee80211-mesh.h
@@ -53,6 +53,24 @@ struct ieee80211_mesh_hwmp_preq_bottom {
 	struct ieee80211_mesh_hwmp_preq_target targets[];
 } __packed;
 
+struct ieee80211_mesh_hwmp_prep_top {
+	u8 flags;
+	u8 hopcount;
+	u8 ttl;
+	u8 target_addr[ETH_ALEN];
+	__le32 target_sn;
+
+	/* optional Target External Address */
+	u8 variable[];
+} __packed;
+
+struct ieee80211_mesh_hwmp_prep_bottom {
+	__le32 lifetime;
+	__le32 metric;
+	u8 orig_addr[ETH_ALEN];
+	__le32 orig_sn;
+} __packed;
+
 /* Mesh flags */
 #define MESH_FLAGS_AE_A4 	0x1
 #define MESH_FLAGS_AE_A5_A6	0x2
@@ -269,4 +287,13 @@ ieee80211_mesh_hwmp_preq_get_bottom(const u8 *ie)
 		ieee80211_mesh_preq_prep_ae_enabled(ie) ? ETH_ALEN : 0];
 }
 
+static inline struct ieee80211_mesh_hwmp_prep_bottom *
+ieee80211_mesh_hwmp_prep_get_bottom(const u8 *ie)
+{
+	struct ieee80211_mesh_hwmp_prep_top *top = (void *)ie;
+
+	return (void *)&top->variable[
+		ieee80211_mesh_preq_prep_ae_enabled(ie) ? ETH_ALEN : 0];
+}
+
 #endif /* LINUX_IEEE80211_MESH_H */
diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index 1a6a22b185d9..39b782370df0 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -37,16 +37,6 @@ static inline u16 u16_field_get(const u8 *preq_elem, int offset, bool ae)
 /* HWMP IE processing macros */
 #define AE_F_SET(x)		(*x & AE_F)
 
-#define PREP_IE_FLAGS(x)	(*(x))
-#define PREP_IE_HOPCOUNT(x)	(*(x + 1))
-#define PREP_IE_TTL(x)		(*(x + 2))
-#define PREP_IE_ORIG_ADDR(x)	(AE_F_SET(x) ? x + 27 : x + 21)
-#define PREP_IE_ORIG_SN(x)	u32_field_get(x, 27, AE_F_SET(x))
-#define PREP_IE_LIFETIME(x)	u32_field_get(x, 13, AE_F_SET(x))
-#define PREP_IE_METRIC(x)	u32_field_get(x, 17, AE_F_SET(x))
-#define PREP_IE_TARGET_ADDR(x)	(x + 3)
-#define PREP_IE_TARGET_SN(x)	u32_field_get(x, 9, 0)
-
 #define PERR_IE_TTL(x)		(*(x))
 #define PERR_IE_TARGET_FLAGS(x)	(*(x + 2))
 #define PERR_IE_TARGET_ADDR(x)	(x + 3)
@@ -419,11 +409,16 @@ static u32 hwmp_route_info_get(struct ieee80211_sub_if_data *sdata,
 		 * so that we can easily use a single function to gather path
 		 * information from both PREQ and PREP frames.
 		 */
-		orig_addr = PREP_IE_TARGET_ADDR(hwmp_ie);
-		orig_sn = PREP_IE_TARGET_SN(hwmp_ie);
-		orig_lifetime = PREP_IE_LIFETIME(hwmp_ie);
-		orig_metric = PREP_IE_METRIC(hwmp_ie);
-		hopcount = PREP_IE_HOPCOUNT(hwmp_ie) + 1;
+		struct ieee80211_mesh_hwmp_prep_top *prep_elem_top =
+			(void *)hwmp_ie;
+		struct ieee80211_mesh_hwmp_prep_bottom *prep_elem_bottom =
+			ieee80211_mesh_hwmp_prep_get_bottom(hwmp_ie);
+
+		orig_addr = prep_elem_top->target_addr;
+		orig_sn = le32_to_cpu(prep_elem_top->target_sn);
+		orig_lifetime = le32_to_cpu(prep_elem_bottom->lifetime);
+		orig_metric = le32_to_cpu(prep_elem_bottom->metric);
+		hopcount = prep_elem_top->hopcount + 1;
 		break;
 	default:
 		rcu_read_unlock();
@@ -714,6 +709,9 @@ static void hwmp_prep_frame_process(struct ieee80211_sub_if_data *sdata,
 				    const u8 *prep_elem, u32 metric)
 {
 	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
+	struct ieee80211_mesh_hwmp_prep_top *prep_elem_top = (void *)prep_elem;
+	struct ieee80211_mesh_hwmp_prep_bottom *prep_elem_bottom =
+		ieee80211_mesh_hwmp_prep_get_bottom(prep_elem);
 	struct mesh_path *mpath;
 	const u8 *target_addr, *orig_addr;
 	u8 ttl, hopcount, flags;
@@ -721,9 +719,9 @@ static void hwmp_prep_frame_process(struct ieee80211_sub_if_data *sdata,
 	u32 target_sn, orig_sn, lifetime;
 
 	mhwmp_dbg(sdata, "received PREP from %pM\n",
-		  PREP_IE_TARGET_ADDR(prep_elem));
+		  prep_elem_top->target_addr);
 
-	orig_addr = PREP_IE_ORIG_ADDR(prep_elem);
+	orig_addr = prep_elem_bottom->orig_addr;
 	if (ether_addr_equal(orig_addr, sdata->vif.addr))
 		/* destination, no forwarding required */
 		return;
@@ -731,7 +729,7 @@ static void hwmp_prep_frame_process(struct ieee80211_sub_if_data *sdata,
 	if (!ifmsh->mshcfg.dot11MeshForwarding)
 		return;
 
-	ttl = PREP_IE_TTL(prep_elem);
+	ttl = prep_elem_top->ttl;
 	if (ttl <= 1) {
 		sdata->u.mesh.mshstats.dropped_frames_ttl++;
 		return;
@@ -750,12 +748,12 @@ static void hwmp_prep_frame_process(struct ieee80211_sub_if_data *sdata,
 	memcpy(next_hop, next_hop_deref_protected(mpath)->sta.addr, ETH_ALEN);
 	spin_unlock_bh(&mpath->state_lock);
 	--ttl;
-	flags = PREP_IE_FLAGS(prep_elem);
-	lifetime = PREP_IE_LIFETIME(prep_elem);
-	hopcount = PREP_IE_HOPCOUNT(prep_elem) + 1;
-	target_addr = PREP_IE_TARGET_ADDR(prep_elem);
-	target_sn = PREP_IE_TARGET_SN(prep_elem);
-	orig_sn = PREP_IE_ORIG_SN(prep_elem);
+	flags = prep_elem_top->flags;
+	lifetime = le32_to_cpu(prep_elem_bottom->lifetime);
+	hopcount = prep_elem_top->hopcount + 1;
+	target_addr = prep_elem_top->target_addr;
+	target_sn = le32_to_cpu(prep_elem_top->target_sn);
+	orig_sn = le32_to_cpu(prep_elem_bottom->orig_sn);
 
 	mesh_path_sel_frame_tx(MPATH_PREP, flags, orig_addr, orig_sn, 0,
 			       target_addr, target_sn, next_hop, hopcount,