[PATCH 1/3] Fix overread in PREQ frame processing

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

When the AF flag is enabled, hwmp_preq_frame_process() overreads target_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_request_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>
---
 net/mac80211/mesh.h      |  1 +
 net/mac80211/mesh_hwmp.c | 35 +++++++++++++++++++++++++++++++++--
 net/mac80211/parse.c     |  7 +++++--
 3 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/net/mac80211/mesh.h b/net/mac80211/mesh.h
index 3f9664e4e00c..331d2d774196 100644
--- a/net/mac80211/mesh.h
+++ b/net/mac80211/mesh.h
@@ -317,6 +317,7 @@ struct mesh_path *
 mpp_path_lookup_by_idx(struct ieee80211_sub_if_data *sdata, int idx);
 void mesh_path_fix_nexthop(struct mesh_path *mpath, struct sta_info *next_hop);
 void mesh_path_expire(struct ieee80211_sub_if_data *sdata);
+u8 mesh_path_parse_request_frame(const u8 *pos, u8 elen);
 void mesh_rx_path_sel_frame(struct ieee80211_sub_if_data *sdata,
 			    struct ieee80211_mgmt *mgmt, size_t len);
 struct mesh_path *
diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index 9d89ebcce1c1..4239412d12c7 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -45,6 +45,7 @@ static inline u16 u16_field_get(const u8 *preq_elem, int offset, bool ae)
 #define PREQ_IE_ORIG_SN(x)	u32_field_get(x, 13, 0)
 #define PREQ_IE_LIFETIME(x)	u32_field_get(x, 17, AE_F_SET(x))
 #define PREQ_IE_METRIC(x) 	u32_field_get(x, 21, AE_F_SET(x))
+#define PREQ_IE_TARGET_COUNT(x)	(*(AE_F_SET(x) ? x + 31 : x + 25))
 #define PREQ_IE_TARGET_F(x)	(*(AE_F_SET(x) ? x + 32 : x + 26))
 #define PREQ_IE_TARGET_ADDR(x) 	(AE_F_SET(x) ? x + 33 : x + 27)
 #define PREQ_IE_TARGET_SN(x) 	u32_field_get(x, 33, AE_F_SET(x))
@@ -924,6 +925,29 @@ static void hwmp_rann_frame_process(struct ieee80211_sub_if_data *sdata,
 	rcu_read_unlock();
 }
 
+/* IEEE Std 802.11-2016 9.4.2.113 PREQ element */
+u8 mesh_path_parse_request_frame(const u8 *pos, u8 elen)
+{
+	u8 target_count;
+	u8 expected_len;
+
+	target_count = PREQ_IE_TARGET_COUNT(pos);
+	if (unlikely(target_count < 1 || target_count > 20))
+		return IEEE80211_PARSE_ERR_UNEXPECTED_ELEM;
+
+	expected_len = 1 /* Flags */ + 1 /* Hop Count */ + 1 /* Element TTL */ +
+		       4 /* Path Discovery ID */ +
+		       6 /* Originator Mesh STA Address */ +
+		       4 /* Originator HWMP Sequence Number */ +
+		       (AE_F_SET(pos) ? 6 : 0) /* Originator External Address */ +
+		       4 /* Lifetime */ + 4 /* Metric */ + 1 + /* Target Count */ +
+		       target_count * (1 /* Per Target Flags */ +
+		       6 /* Target Address */ + 4 /* Target HWMP Sequence Number */);
+	if (unlikely(elen != expected_len))
+		return IEEE80211_PARSE_ERR_BAD_ELEM_SIZE;
+
+	return 0;
+}
 
 void mesh_rx_path_sel_frame(struct ieee80211_sub_if_data *sdata,
 			    struct ieee80211_mgmt *mgmt, size_t len)
@@ -932,6 +956,7 @@ void mesh_rx_path_sel_frame(struct ieee80211_sub_if_data *sdata,
 	size_t baselen;
 	u32 path_metric;
 	struct sta_info *sta;
+	u8 target_count;
 
 	/* need action_code */
 	if (len < IEEE80211_MIN_ACTION_SIZE(mesh_action))
@@ -955,9 +980,15 @@ void mesh_rx_path_sel_frame(struct ieee80211_sub_if_data *sdata,
 		return;
 
 	if (elems->preq) {
-		if (elems->preq_len != 37)
-			/* Right now we support just 1 destination and no AE */
+		/* Right now we do not support AE (Address Extension) */
+		if (AE_F_SET(elems->preq))
 			goto free;
+
+		/* Right now we only supports 1 target */
+		target_count = PREQ_IE_TARGET_COUNT(elems->preq);
+		if (target_count != 1)
+			goto free;
+
 		path_metric = hwmp_route_info_get(sdata, mgmt, elems->preq,
 						  MPATH_PREQ);
 		if (path_metric)
diff --git a/net/mac80211/parse.c b/net/mac80211/parse.c
index 5e61457be0f3..7a2abe676361 100644
--- a/net/mac80211/parse.c
+++ b/net/mac80211/parse.c
@@ -547,8 +547,11 @@ _ieee802_11_parse_elems_full(struct ieee80211_elems_parse_params *params,
 				elems->awake_window = (void *)pos;
 			break;
 		case WLAN_EID_PREQ:
-			elems->preq = pos;
-			elems->preq_len = elen;
+			elem_parse_failed = mesh_path_parse_request_frame(pos, elen);
+			if (likely(!elem_parse_failed)) {
+				elems->preq = pos;
+				elems->preq_len = elen;
+			}
 			break;
 		case WLAN_EID_PREP:
 			elems->prep = pos;
-- 
2.43.0