[PATCH 2/3] Fix overread in PREP frame processing

[Masashi Honma <masashi.honma@gmail.com>]

When the AF flag is enabled, hwmp_prep_frame_process() overreads orig_addr
by 2 bytes. Since this occurs within the socket buffer, it does not read across
memory boundaries and therefore poses no security risk; however, we will fix it
as a precaution.

In this fix, a new function mesh_path_parse_reply_frame() is established to
separate the implementation of frame format validation and the check for
unsupported features. This is intended to facilitate future work when
implementing the currently unsupported parts.

Assisted-by: Claude:Sonnet 4.6
Signed-off-by: Masashi Honma <masashi.honma@gmail.com>
---
 include/linux/ieee80211-mesh.h | 18 ++++++++++++++++++
 net/mac80211/mesh_hwmp.c       |  5 +++--
 net/mac80211/parse.c           |  9 +++++++--
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/include/linux/ieee80211-mesh.h b/include/linux/ieee80211-mesh.h
index 8ff68cf539ff..ddbf475c1cc8 100644
--- a/include/linux/ieee80211-mesh.h
+++ b/include/linux/ieee80211-mesh.h
@@ -283,4 +283,22 @@ static inline bool ieee80211_mesh_preq_size_ok(const u8 *pos, u8 elen)
 	return true;
 }
 
+/* IEEE Std 802.11-2016 9.4.2.114 PREP element */
+static inline bool ieee80211_mesh_prep_size_ok(const u8 *pos, u8 elen)
+{
+	u8 needed;
+
+	needed = 1 /* Flags */ + 1 /* Hop Count */ + 1 /* Element TTL */ +
+		 6 /* Target Mesh STA Address */ +
+		 4 /* Target HWMP Sequence Number */ +
+		 (AE_F_SET(pos) ? 6 : 0) /* Target External Address */ +
+		 4 /* Lifetime */ + 4 /* Metric */ +
+		 6 /* Originator Mesh STA Address */ +
+		 4 /* Originator HWMP Sequence Number */;
+	if (elen != needed)
+		return false;
+
+	return true;
+}
+
 #endif /* LINUX_IEEE80211_MESH_H */
diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index a4984b015995..c70cfc2d6299 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -941,9 +941,10 @@ void mesh_rx_path_sel_frame(struct ieee80211_sub_if_data *sdata,
 						path_metric);
 	}
 	if (elems->prep) {
-		if (elems->prep_len != 31)
-			/* Right now we support no AE */
+		/* Right now we do not support AE (Address Extension) */
+		if (AE_F_SET(elems->prep))
 			goto free;
+
 		path_metric = hwmp_route_info_get(sdata, mgmt, elems->prep,
 						  MPATH_PREP);
 		if (path_metric)
diff --git a/net/mac80211/parse.c b/net/mac80211/parse.c
index 9e52cc48fc18..bbd1e1bc77b4 100644
--- a/net/mac80211/parse.c
+++ b/net/mac80211/parse.c
@@ -556,8 +556,13 @@ _ieee802_11_parse_elems_full(struct ieee80211_elems_parse_params *params,
 			}
 			break;
 		case WLAN_EID_PREP:
-			elems->prep = pos;
-			elems->prep_len = elen;
+			if (ieee80211_mesh_prep_size_ok(pos, elen)) {
+				elems->prep = pos;
+				elems->prep_len = elen;
+			} else {
+				elem_parse_failed =
+					IEEE80211_PARSE_ERR_BAD_ELEM_SIZE;
+			}
 			break;
 		case WLAN_EID_PERR:
 			elems->perr = pos;
-- 
2.43.0