[PATCH v8 4/6] wifi: mac80211: 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>
---
 include/linux/ieee80211-mesh.h | 28 ++++++++++++++++++++++++++++
 net/mac80211/mesh_hwmp.c       | 12 ++++++++++--
 net/mac80211/parse.c           |  9 +++++++--
 3 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/include/linux/ieee80211-mesh.h b/include/linux/ieee80211-mesh.h
index 0e9bd56b54f2..42a5bd73838c 100644
--- a/include/linux/ieee80211-mesh.h
+++ b/include/linux/ieee80211-mesh.h
@@ -321,4 +321,32 @@ ieee80211_mesh_hwmp_perr_get_rcode(const u8 *ie, u8 dst_idx)
 		(dst->flags & AE_F) ? ETH_ALEN : 0]);
 }
 
+/* IEEE Std 802.11-2016 9.4.2.113 PREQ element */
+static inline bool ieee80211_mesh_preq_size_ok(const u8 *pos, u8 elen)
+{
+	struct ieee80211_mesh_hwmp_preq_bottom *preq_elem_bottom =
+		ieee80211_mesh_hwmp_preq_get_bottom(pos);
+	u8 target_count;
+	u8 needed;
+
+	/* Check if the element contains flags */
+	if (elen < 1)
+		return false;
+
+	/* Check if the element contains target_count */
+	needed = sizeof(struct ieee80211_mesh_hwmp_preq_top) +
+		 (ieee80211_mesh_preq_prep_ae_enabled(pos) ? ETH_ALEN : 0)
+		 /* Originator External Address */ +
+		 sizeof(struct ieee80211_mesh_hwmp_preq_bottom);
+	if (elen < needed)
+		return false;
+
+	target_count = preq_elem_bottom->target_count;
+	if (target_count < 1 || target_count > 20)
+		return false;
+
+	needed += target_count * sizeof(struct ieee80211_mesh_hwmp_preq_target);
+	return elen == needed;
+}
+
 #endif /* LINUX_IEEE80211_MESH_H */
diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index fa144a187fe2..ad3e575a0a94 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -929,9 +929,17 @@ 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 */
+		struct ieee80211_mesh_hwmp_preq_bottom *preq_elem_bottom =
+			ieee80211_mesh_hwmp_preq_get_bottom(elems->preq);
+
+		/* Right now we do not support AE (Address Extension) */
+		if (ieee80211_mesh_preq_prep_ae_enabled(elems->preq))
 			goto free;
+
+		/* Right now we only support 1 target */
+		if (preq_elem_bottom->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..9e52cc48fc18 100644
--- a/net/mac80211/parse.c
+++ b/net/mac80211/parse.c
@@ -547,8 +547,13 @@ _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;
+			if (ieee80211_mesh_preq_size_ok(pos, elen)) {
+				elems->preq = pos;
+				elems->preq_len = elen;
+			} else {
+				elem_parse_failed =
+					IEEE80211_PARSE_ERR_BAD_ELEM_SIZE;
+			}
 			break;
 		case WLAN_EID_PREP:
 			elems->prep = pos;
-- 
2.43.0