FILS: Add DHss into FILS-Key-Data derivation when using FILS SK+PFS

This part is missing from IEEE Std 802.11ai-2016, but the lack of DHss
here means there would not be proper PFS for the case where PMKSA
caching is used with FILS SK+PFS authentication. This was not really the
intent of the FILS design and that issue was fixed during REVmd work
with the changes proposed in
https://mentor.ieee.org/802.11/dcn/17/11-17-0906-04-000m-fils-fixes.docx
that add DHss into FILS-Key-Data (and PTK, in practice) derivation for
the PMKSA caching case so that a unique ICK, KEK, and TK are derived
even when using the same PMK.

Note: This is not backwards compatible, i.e., this breaks PMKSA caching
with FILS SK+PFS if only STA or AP side implementation is updated.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/ap/ieee802_11.c

@@ -1417,6 +1417,11 @@ prepare_auth_resp_fils(struct hostapd_data *hapd,
 		}
 		pmk = pmk_buf;
 
+		/* Don't use DHss in PTK derivation if PMKSA caching is not
+		 * used. */
+		wpabuf_clear_free(sta->fils_dh_ss);
+		sta->fils_dh_ss = NULL;
+
 		if (sta->fils_erp_pmkid_set) {
 			/* TODO: get PMKLifetime from WPA parameters */
 			unsigned int dot11RSNAConfigPMKLifetime = 43200;
@@ -1449,6 +1454,10 @@ prepare_auth_resp_fils(struct hostapd_data *hapd,
 
 	if (fils_auth_pmk_to_ptk(sta->wpa_sm, pmk, pmk_len,
 				 sta->fils_snonce, fils_nonce,
+				 sta->fils_dh_ss ?
+				 wpabuf_head(sta->fils_dh_ss) : NULL,
+				 sta->fils_dh_ss ?
+				 wpabuf_len(sta->fils_dh_ss) : 0,
 				 sta->fils_g_sta, pub) < 0) {
 		*resp = WLAN_STATUS_UNSPECIFIED_FAILURE;
 		wpabuf_free(data);

src/ap/wpa_auth.c

@@ -2113,6 +2113,7 @@ static int wpa_derive_ptk(struct wpa_state_machine *sm, const u8 *snonce,
 
 int fils_auth_pmk_to_ptk(struct wpa_state_machine *sm, const u8 *pmk,
 			 size_t pmk_len, const u8 *snonce, const u8 *anonce,
+			 const u8 *dhss, size_t dhss_len,
 			 struct wpabuf *g_sta, struct wpabuf *g_ap)
 {
 	u8 ick[FILS_ICK_MAX_LEN];
@@ -2122,7 +2123,8 @@ int fils_auth_pmk_to_ptk(struct wpa_state_machine *sm, const u8 *pmk,
 	size_t fils_ft_len = 0;
 
 	res = fils_pmk_to_ptk(pmk, pmk_len, sm->addr, sm->wpa_auth->addr,
-			      snonce, anonce, &sm->PTK, ick, &ick_len,
+			      snonce, anonce, dhss, dhss_len,
+			      &sm->PTK, ick, &ick_len,
 			      sm->wpa_key_mgmt, sm->pairwise,
 			      fils_ft, &fils_ft_len);
 	if (res < 0)

src/ap/wpa_auth.h

@@ -400,6 +400,7 @@ int wpa_auth_ensure_group(struct wpa_authenticator *wpa_auth, int vlan_id);
 int wpa_auth_release_group(struct wpa_authenticator *wpa_auth, int vlan_id);
 int fils_auth_pmk_to_ptk(struct wpa_state_machine *sm, const u8 *pmk,
 			 size_t pmk_len, const u8 *snonce, const u8 *anonce,
+			 const u8 *dhss, size_t dhss_len,
 			 struct wpabuf *g_sta, struct wpabuf *g_ap);
 int fils_decrypt_assoc(struct wpa_state_machine *sm, const u8 *fils_session,
 		       const struct ieee80211_mgmt *mgmt, size_t frame_len,

src/common/wpa_common.c

@@ -389,19 +389,22 @@ int fils_pmkid_erp(int akmp, const u8 *reauth, size_t reauth_len,
 
 
 int fils_pmk_to_ptk(const u8 *pmk, size_t pmk_len, const u8 *spa, const u8 *aa,
-		    const u8 *snonce, const u8 *anonce, struct wpa_ptk *ptk,
+		    const u8 *snonce, const u8 *anonce, const u8 *dhss,
+		    size_t dhss_len, struct wpa_ptk *ptk,
 		    u8 *ick, size_t *ick_len, int akmp, int cipher,
 		    u8 *fils_ft, size_t *fils_ft_len)
 {
-	u8 data[2 * ETH_ALEN + 2 * FILS_NONCE_LEN];
+	u8 *data, *pos;
+	size_t data_len;
 	u8 tmp[FILS_ICK_MAX_LEN + WPA_KEK_MAX_LEN + WPA_TK_MAX_LEN +
 	       FILS_FT_MAX_LEN];
 	size_t key_data_len;
 	const char *label = "FILS PTK Derivation";
+	int ret = -1;
 
 	/*
 	 * FILS-Key-Data = PRF-X(PMK, "FILS PTK Derivation",
-	 *                       SPA || AA || SNonce || ANonce)
+	 *                       SPA || AA || SNonce || ANonce [ || DHss ])
 	 * ICK = L(FILS-Key-Data, 0, ICK_bits)
 	 * KEK = L(FILS-Key-Data, ICK_bits, KEK_bits)
 	 * TK = L(FILS-Key-Data, ICK_bits + KEK_bits, TK_bits)
@@ -409,10 +412,21 @@ int fils_pmk_to_ptk(const u8 *pmk, size_t pmk_len, const u8 *spa, const u8 *aa,
 	 * FILS-FT = L(FILS-Key-Data, ICK_bits + KEK_bits + TK_bits,
 	 *             FILS-FT_bits)
 	 */
-	os_memcpy(data, spa, ETH_ALEN);
-	os_memcpy(data + ETH_ALEN, aa, ETH_ALEN);
-	os_memcpy(data + 2 * ETH_ALEN, snonce, FILS_NONCE_LEN);
-	os_memcpy(data + 2 * ETH_ALEN + FILS_NONCE_LEN, anonce, FILS_NONCE_LEN);
+	data_len = 2 * ETH_ALEN + 2 * FILS_NONCE_LEN + dhss_len;
+	data = os_malloc(data_len);
+	if (!data)
+		goto err;
+	pos = data;
+	os_memcpy(pos, spa, ETH_ALEN);
+	pos += ETH_ALEN;
+	os_memcpy(pos, aa, ETH_ALEN);
+	pos += ETH_ALEN;
+	os_memcpy(pos, snonce, FILS_NONCE_LEN);
+	pos += FILS_NONCE_LEN;
+	os_memcpy(pos, anonce, FILS_NONCE_LEN);
+	pos += FILS_NONCE_LEN;
+	if (dhss)
+		os_memcpy(pos, dhss, dhss_len);
 
 	ptk->kck_len = 0;
 	ptk->kek_len = wpa_kek_len(akmp, pmk_len);
@@ -422,7 +436,7 @@ int fils_pmk_to_ptk(const u8 *pmk, size_t pmk_len, const u8 *spa, const u8 *aa,
 	else if (wpa_key_mgmt_sha256(akmp))
 		*ick_len = 32;
 	else
-		return -1;
+		goto err;
 	key_data_len = *ick_len + ptk->kek_len + ptk->tk_len;
 
 	if (fils_ft && fils_ft_len) {
@@ -439,20 +453,22 @@ int fils_pmk_to_ptk(const u8 *pmk, size_t pmk_len, const u8 *spa, const u8 *aa,
 
 	if (wpa_key_mgmt_sha384(akmp)) {
 		wpa_printf(MSG_DEBUG, "FILS: PTK derivation using PRF(SHA384)");
-		if (sha384_prf(pmk, pmk_len, label, data, sizeof(data),
+		if (sha384_prf(pmk, pmk_len, label, data, data_len,
 			       tmp, key_data_len) < 0)
-			return -1;
+			goto err;
 	} else {
 		wpa_printf(MSG_DEBUG, "FILS: PTK derivation using PRF(SHA256)");
-		if (sha256_prf(pmk, pmk_len, label, data, sizeof(data),
+		if (sha256_prf(pmk, pmk_len, label, data, data_len,
 			       tmp, key_data_len) < 0)
-			return -1;
+			goto err;
 	}
 
 	wpa_printf(MSG_DEBUG, "FILS: PTK derivation - SPA=" MACSTR
 		   " AA=" MACSTR, MAC2STR(spa), MAC2STR(aa));
 	wpa_hexdump(MSG_DEBUG, "FILS: SNonce", snonce, FILS_NONCE_LEN);
 	wpa_hexdump(MSG_DEBUG, "FILS: ANonce", anonce, FILS_NONCE_LEN);
+	if (dhss)
+		wpa_hexdump_key(MSG_DEBUG, "FILS: DHss", dhss, dhss_len);
 	wpa_hexdump_key(MSG_DEBUG, "FILS: PMK", pmk, pmk_len);
 	wpa_hexdump_key(MSG_DEBUG, "FILS: FILS-Key-Data", tmp, key_data_len);
 
@@ -473,7 +489,10 @@ int fils_pmk_to_ptk(const u8 *pmk, size_t pmk_len, const u8 *spa, const u8 *aa,
 	}
 
 	os_memset(tmp, 0, sizeof(tmp));
-	return 0;
+	ret = 0;
+err:
+	bin_clear_free(data, data_len);
+	return ret;
 }
 
 

src/common/wpa_common.h

@@ -347,7 +347,8 @@ int fils_rmsk_to_pmk(int akmp, const u8 *rmsk, size_t rmsk_len,
 int fils_pmkid_erp(int akmp, const u8 *reauth, size_t reauth_len,
 		   u8 *pmkid);
 int fils_pmk_to_ptk(const u8 *pmk, size_t pmk_len, const u8 *spa, const u8 *aa,
-		    const u8 *snonce, const u8 *anonce, struct wpa_ptk *ptk,
+		    const u8 *snonce, const u8 *anonce, const u8 *dhss,
+		    size_t dhss_len, struct wpa_ptk *ptk,
 		    u8 *ick, size_t *ick_len, int akmp, int cipher,
 		    u8 *fils_ft, size_t *fils_ft_len);
 int fils_key_auth_sk(const u8 *ick, size_t ick_len, const u8 *snonce,

src/rsn_supp/wpa.c

@@ -3639,8 +3639,12 @@ int fils_process_auth(struct wpa_sm *sm, const u8 *bssid, const u8 *data,
 				       dh_ss ? wpabuf_len(dh_ss) : 0,
 				       sm->pmk, &sm->pmk_len);
 		os_memset(rmsk, 0, sizeof(rmsk));
+
+		/* Don't use DHss in PTK derivation if PMKSA caching is not
+		 * used. */
 		wpabuf_clear_free(dh_ss);
 		dh_ss = NULL;
+
 		if (res)
 			goto fail;
 
@@ -3665,12 +3669,19 @@ int fils_process_auth(struct wpa_sm *sm, const u8 *bssid, const u8 *data,
 	}
 
 	if (fils_pmk_to_ptk(sm->pmk, sm->pmk_len, sm->own_addr, sm->bssid,
-			    sm->fils_nonce, sm->fils_anonce, &sm->ptk,
-			    ick, &ick_len, sm->key_mgmt, sm->pairwise_cipher,
+			    sm->fils_nonce, sm->fils_anonce,
+			    dh_ss ? wpabuf_head(dh_ss) : NULL,
+			    dh_ss ? wpabuf_len(dh_ss) : 0,
+			    &sm->ptk, ick, &ick_len,
+			    sm->key_mgmt, sm->pairwise_cipher,
 			    sm->fils_ft, &sm->fils_ft_len) < 0) {
 		wpa_printf(MSG_DEBUG, "FILS: Failed to derive PTK");
 		goto fail;
 	}
+
+	wpabuf_clear_free(dh_ss);
+	dh_ss = NULL;
+
 	sm->ptk_set = 1;
 	sm->tptk_set = 0;
 	os_memset(&sm->tptk, 0, sizeof(sm->tptk));

wlantest/rx_mgmt.c

@@ -351,7 +351,8 @@ static int try_rmsk(struct wlantest *wt, struct wlantest_bss *bss,
 		return -1;
 
 	if (fils_pmk_to_ptk(pmk_buf, pmk_len, sta->addr, bss->bssid,
-			    sta->snonce, sta->anonce, &ptk, ick, &ick_len,
+			    sta->snonce, sta->anonce, NULL, 0,
+			    &ptk, ick, &ick_len,
 			    sta->key_mgmt, sta->pairwise_cipher,
 			    NULL, NULL) < 0)
 		return -1;