mac80211: fix and improve mesh RANN processing

This patch fixes the problem of dropping RANN element if the TTL
is 1. If the received RANN element TTL is 1 or greater than 1, the
RANN is processed. However, forwarding of received RANN element
with TTL 1 or less is prohibited according to the standard. This
is previously reported by Monthadar Al Jaberi.

Besides, this patch also avoid the processing of unicast PREQ
generation if the RANN element does not meet the acceptance
criteria mentioned in Sec. 13.10.12.4.2 of IEEE Std. 802.11-2012.
Reported-by: Monthadar Al Jaberi <monthadar@gmail.com>
Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mesh_hwmp.c

@@ -771,11 +771,6 @@ static void hwmp_rann_frame_process(struct ieee80211_sub_if_data *sdata,
 	bool root_is_gate;
 
 	ttl = rann->rann_ttl;
-	if (ttl <= 1) {
-		ifmsh->mshstats.dropped_frames_ttl++;
-		return;
-	}
-	ttl--;
 	flags = rann->rann_flags;
 	root_is_gate = !!(flags & RANN_FLAG_IS_GATE);
 	orig_addr = rann->rann_addr;
@@ -812,37 +807,49 @@ static void hwmp_rann_frame_process(struct ieee80211_sub_if_data *sdata,
 		}
 	}
 
+	if (!(SN_LT(mpath->sn, orig_sn)) &&
+	    !(mpath->sn == orig_sn && metric < mpath->rann_metric)) {
+		rcu_read_unlock();
+		return;
+	}
+
 	if ((!(mpath->flags & (MESH_PATH_ACTIVE | MESH_PATH_RESOLVING)) ||
 	     (time_after(jiffies, mpath->last_preq_to_root +
 				  root_path_confirmation_jiffies(sdata)) ||
 	     time_before(jiffies, mpath->last_preq_to_root))) &&
-	     !(mpath->flags & MESH_PATH_FIXED)) {
+	     !(mpath->flags & MESH_PATH_FIXED) && (ttl != 0)) {
 		mhwmp_dbg("%s time to refresh root mpath %pM", sdata->name,
 							       orig_addr);
 		mesh_queue_preq(mpath, PREQ_Q_F_START | PREQ_Q_F_REFRESH);
 		mpath->last_preq_to_root = jiffies;
 	}
 
-	if ((SN_LT(mpath->sn, orig_sn) || (mpath->sn == orig_sn &&
-	   metric < mpath->rann_metric)) && ifmsh->mshcfg.dot11MeshForwarding) {
-		mesh_path_sel_frame_tx(MPATH_RANN, flags, orig_addr,
-				       cpu_to_le32(orig_sn),
-				       0, NULL, 0, broadcast_addr,
-				       hopcount, ttl, cpu_to_le32(interval),
-				       cpu_to_le32(metric + metric_txsta),
-				       0, sdata);
 	mpath->sn = orig_sn;
 	mpath->rann_metric = metric + metric_txsta;
+	mpath->is_root = true;
 	/* Recording RANNs sender address to send individually
 	 * addressed PREQs destined for root mesh STA */
 	memcpy(mpath->rann_snd_addr, mgmt->sa, ETH_ALEN);
-	}
-
-	mpath->is_root = true;
 
 	if (root_is_gate)
 		mesh_path_add_gate(mpath);
 
+	if (ttl <= 1) {
+		ifmsh->mshstats.dropped_frames_ttl++;
+		rcu_read_unlock();
+		return;
+	}
+	ttl--;
+
+	if (ifmsh->mshcfg.dot11MeshForwarding) {
+		mesh_path_sel_frame_tx(MPATH_RANN, flags, orig_addr,
+				       cpu_to_le32(orig_sn),
+				       0, NULL, 0, broadcast_addr,
+				       hopcount, ttl, cpu_to_le32(interval),
+				       cpu_to_le32(metric + metric_txsta),
+				       0, sdata);
+	}
+
 	rcu_read_unlock();
 }