mesh: Fix mesh SAE auth on low spec devices

The mesh SAE auth often fails with master branch. By bisect I found
commit eb5fee0bf5 ('SAE: Add side-channel
protection to PWE derivation with ECC') causes this issue. This does not
mean the commit has a bug. This is just a CPU resource issue.

After the commit, sae_derive_pwe_ecc() spends 101(msec) on my PC (Intel
Atom N270 1.6GHz). But dot11RSNASAERetransPeriod is 40(msec). So
auth_sae_retransmit_timer() is always called and it can causes
continuous frame exchanges. Before the commit, it was 23(msec).

On the IEEE 802.11 spec, the default value of dot11RSNASAERetransPeriod
is defined as 40(msec). But it looks short because generally mesh
functionality will be used on low spec devices. Indeed Raspberry Pi B+
(ARM ARM1176JZF-S 700MHz) requires 287(msec) for new
sae_derive_pwe_ecc().

So this patch makes the default to 1000(msec) and makes it configurable.

This issue does not occur on infrastructure SAE because the
dot11RSNASAERetransPeriod is not used on it.

Signed-off-by: Masashi Honma <masashi.honma@gmail.com>

src/ap/hostapd.h

@@ -269,6 +269,7 @@ struct hostapd_data {
 	/** Key used for generating SAE anti-clogging tokens */
 	u8 sae_token_key[8];
 	struct os_reltime last_sae_token_key_update;
+	int dot11RSNASAERetransPeriod; /* msec */
 #endif /* CONFIG_SAE */
 
 #ifdef CONFIG_TESTING_OPTIONS

src/ap/ieee802_11.c

@@ -316,7 +316,6 @@ static void handle_auth_ft_finish(void *ctx, const u8 *dst, const u8 *bssid,
 
 #ifdef CONFIG_SAE
 
-#define dot11RSNASAERetransPeriod 40	/* msec */
 #define dot11RSNASAESync 5		/* attempts */
 
 
@@ -499,12 +498,14 @@ static void auth_sae_retransmit_timer(void *eloop_ctx, void *eloop_data)
 	switch (sta->sae->state) {
 	case SAE_COMMITTED:
 		ret = auth_sae_send_commit(hapd, sta, hapd->own_addr, 0);
-		eloop_register_timeout(0, dot11RSNASAERetransPeriod * 1000,
+		eloop_register_timeout(0,
+				       hapd->dot11RSNASAERetransPeriod * 1000,
 				       auth_sae_retransmit_timer, hapd, sta);
 		break;
 	case SAE_CONFIRMED:
 		ret = auth_sae_send_confirm(hapd, sta, hapd->own_addr);
-		eloop_register_timeout(0, dot11RSNASAERetransPeriod * 1000,
+		eloop_register_timeout(0,
+				       hapd->dot11RSNASAERetransPeriod * 1000,
 				       auth_sae_retransmit_timer, hapd, sta);
 		break;
 	default:
@@ -530,7 +531,7 @@ static void sae_set_retransmit_timer(struct hostapd_data *hapd,
 		return;
 
 	eloop_cancel_timeout(auth_sae_retransmit_timer, hapd, sta);
-	eloop_register_timeout(0, dot11RSNASAERetransPeriod * 1000,
+	eloop_register_timeout(0, hapd->dot11RSNASAERetransPeriod * 1000,
 			       auth_sae_retransmit_timer, hapd, sta);
 }
 

wpa_supplicant/config.c

@@ -3517,6 +3517,8 @@ struct wpa_config * wpa_config_alloc_empty(const char *ctrl_interface,
 	config->user_mpm = DEFAULT_USER_MPM;
 	config->max_peer_links = DEFAULT_MAX_PEER_LINKS;
 	config->mesh_max_inactivity = DEFAULT_MESH_MAX_INACTIVITY;
+	config->dot11RSNASAERetransPeriod =
+		DEFAULT_DOT11_RSNA_SAE_RETRANS_PERIOD;
 	config->fast_reauth = DEFAULT_FAST_REAUTH;
 	config->p2p_go_intent = DEFAULT_P2P_GO_INTENT;
 	config->p2p_intra_bss = DEFAULT_P2P_INTRA_BSS;
@@ -4130,6 +4132,7 @@ static const struct global_parse_data global_fields[] = {
 	{ INT(user_mpm), 0 },
 	{ INT_RANGE(max_peer_links, 0, 255), 0 },
 	{ INT(mesh_max_inactivity), 0 },
+	{ INT(dot11RSNASAERetransPeriod), 0 },
 #endif /* CONFIG_MESH */
 	{ INT(disable_scan_offload), 0 },
 	{ INT(fast_reauth), 0 },

wpa_supplicant/config.h

@@ -18,6 +18,11 @@
 #define DEFAULT_USER_MPM 1
 #define DEFAULT_MAX_PEER_LINKS 99
 #define DEFAULT_MESH_MAX_INACTIVITY 300
+/*
+ * The default dot11RSNASAERetransPeriod is defined as 40 ms in the standard,
+ * but use 1000 ms in practice to avoid issues on low power CPUs.
+ */
+#define DEFAULT_DOT11_RSNA_SAE_RETRANS_PERIOD 1000
 #define DEFAULT_FAST_REAUTH 1
 #define DEFAULT_P2P_GO_INTENT 7
 #define DEFAULT_P2P_INTRA_BSS 1
@@ -1160,6 +1165,15 @@ struct wpa_config {
 	 */
 	int mesh_max_inactivity;
 
+	/**
+	 * dot11RSNASAERetransPeriod - Timeout to retransmit SAE Auth frame
+	 *
+	 * This timeout value is used in mesh STA to retransmit
+	 * SAE Authentication frame.
+	 * By default: 1000 milliseconds.
+	 */
+	int dot11RSNASAERetransPeriod;
+
 	/**
 	 * passive_scan - Whether to force passive scan for network connection
 	 *

wpa_supplicant/config_file.c

@@ -1282,6 +1282,11 @@ static void wpa_config_write_global(FILE *f, struct wpa_config *config)
 		fprintf(f, "mesh_max_inactivity=%d\n",
 			config->mesh_max_inactivity);
 
+	if (config->dot11RSNASAERetransPeriod !=
+	    DEFAULT_DOT11_RSNA_SAE_RETRANS_PERIOD)
+		fprintf(f, "dot11RSNASAERetransPeriod=%d\n",
+			config->dot11RSNASAERetransPeriod);
+
 	if (config->passive_scan)
 		fprintf(f, "passive_scan=%d\n", config->passive_scan);
 

wpa_supplicant/mesh.c

@@ -171,6 +171,8 @@ static int wpa_supplicant_mesh_init(struct wpa_supplicant *wpa_s,
 	ifmsh->conf = conf;
 
 	ifmsh->bss[0]->max_plinks = wpa_s->conf->max_peer_links;
+	ifmsh->bss[0]->dot11RSNASAERetransPeriod =
+		wpa_s->conf->dot11RSNASAERetransPeriod;
 	os_strlcpy(bss->conf->iface, wpa_s->ifname, sizeof(bss->conf->iface));
 
 	mconf = mesh_config_create(ssid);

wpa_supplicant/wpa_cli.c

@@ -618,6 +618,7 @@ static char ** wpa_cli_complete_set(const char *str, int pos)
 		"eapol_version", "ap_scan", "bgscan",
 #ifdef CONFIG_MESH
 		"user_mpm", "max_peer_links", "mesh_max_inactivity",
+		"dot11RSNASAERetransPeriod",
 #endif /* CONFIG_MESH */
 		"disable_scan_offload", "fast_reauth", "opensc_engine_path",
 		"pkcs11_engine_path", "pkcs11_module_path", "openssl_ciphers",