wifi: mac80211: fix race in mesh sequence number assignment

Since the sequence number is shared across different tx queues, it needs
to be atomic in order to avoid accidental duplicate assignment
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20230314095956.62085-2-nbd@nbd.nameSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ieee80211_i.h

@@ -696,7 +696,7 @@ struct ieee80211_if_mesh {
 	struct mesh_stats mshstats;
 	struct mesh_config mshcfg;
 	atomic_t estab_plinks;
-	u32 mesh_seqnum;
+	atomic_t mesh_seqnum;
 	bool accepting_plinks;
 	int num_gates;
 	struct beacon_data __rcu *beacon;

net/mac80211/mesh.c

@@ -752,10 +752,8 @@ unsigned int ieee80211_new_mesh_header(struct ieee80211_sub_if_data *sdata,
 
 	meshhdr->ttl = sdata->u.mesh.mshcfg.dot11MeshTTL;
 
-	/* FIXME: racy -- TX on multiple queues can be concurrent */
-	put_unaligned(cpu_to_le32(sdata->u.mesh.mesh_seqnum), &meshhdr->seqnum);
-	sdata->u.mesh.mesh_seqnum++;
-
+	put_unaligned_le32(atomic_inc_return(&sdata->u.mesh.mesh_seqnum),
+			   &meshhdr->seqnum);
 	if (addr4or5 && !addr6) {
 		meshhdr->flags |= MESH_FLAGS_AE_A4;
 		memcpy(meshhdr->eaddr1, addr4or5, ETH_ALEN);