From 16d4f1069118aa19bfce013493e1ac5783f92f1d Mon Sep 17 00:00:00 2001
From: Jouni Malinen <[email protected]>
Date: Fri, 5 Apr 2019 02:12:50 +0300
Subject: EAP-pwd: Check element x,y coordinates explicitly

This adds an explicit check for 0 < x,y < prime based on RFC 5931,
2.8.5.2.2 requirement. The earlier checks might have covered this
implicitly, but it is safer to avoid any dependency on implicit checks
and specific crypto library behavior. (CVE-2019-9498 and CVE-2019-9499)

Furthermore, this moves the EAP-pwd element and scalar parsing and
validation steps into shared helper functions so that there is no need
to maintain two separate copies of this common functionality between the
server and peer implementations.

Signed-off-by: Jouni Malinen <[email protected]>
backport addr https://w1.fi/cgit/hostap/patch/?id=16d4f1069118aa19bfce013493e1ac5783f92f1d
              https://w1.fi/cgit/hostap/patch/?id=70ff850e89fbc8bc7da515321b4d15b5eef70581
              https://w1.fi/cgit/hostap/patch/?id=8ad8585f91823ddcc3728155e288e0f9f872e31a
---
 src/eap_common/eap_pwd_common.c | 106 ++++++++++++++++++++++++++++++++
 src/eap_common/eap_pwd_common.h |   3 +
 src/eap_peer/eap_pwd.c          |  19 +-----
 src/eap_server/eap_server_pwd.c |  19 +-----
 4 files changed, 111 insertions(+), 36 deletions(-)

diff --git a/src/eap_common/eap_pwd_common.c b/src/eap_common/eap_pwd_common.c
index 67f8f70..ef47db1 100644
--- a/src/eap_common/eap_pwd_common.c
+++ b/src/eap_common/eap_pwd_common.c
@@ -365,3 +365,109 @@ int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, const BIGNUM *k,
 
 	return 1;
 }
+
+
+static int eap_pwd_element_coord_ok(const struct crypto_bignum *prime,
+				    const u8 *buf, size_t len)
+{
+	struct crypto_bignum *val;
+	int ok = 1;
+
+	val = crypto_bignum_init_set(buf, len);
+	if (!val || crypto_bignum_is_zero(val) ||
+	    crypto_bignum_cmp(val, prime) >= 0)
+		ok = 0;
+	crypto_bignum_deinit(val, 0);
+	return ok;
+}
+
+
+struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
+					     const u8 *buf)
+{
+	struct crypto_ec_point *element;
+	const struct crypto_bignum *prime;
+	size_t prime_len;
+	struct crypto_bignum *cofactor = NULL;
+
+	prime = crypto_ec_get_prime(group->group);
+	prime_len = crypto_ec_prime_len(group->group);
+
+	/* RFC 5931, 2.8.5.2.2: 0 < x,y < p */
+	if (!eap_pwd_element_coord_ok(prime, buf, prime_len) ||
+	    !eap_pwd_element_coord_ok(prime, buf + prime_len, prime_len)) {
+		wpa_printf(MSG_INFO, "EAP-pwd: Invalid coordinate in element");
+		return NULL;
+	}
+
+	element = crypto_ec_point_from_bin(group->group, buf);
+	if (!element) {
+		wpa_printf(MSG_INFO, "EAP-pwd: EC point from element failed");
+		return NULL;
+	}
+
+	/* RFC 5931, 2.8.5.2.2: on curve and not the point at infinity */
+	if (!crypto_ec_point_is_on_curve(group->group, element) ||
+	    crypto_ec_point_is_at_infinity(group->group, element)) {
+		wpa_printf(MSG_INFO, "EAP-pwd: Invalid element");
+		goto fail;
+	}
+
+	cofactor = crypto_bignum_init();
+	if (!cofactor || crypto_ec_cofactor(group->group, cofactor) < 0) {
+		wpa_printf(MSG_INFO,
+			   "EAP-pwd: Unable to get cofactor for curve");
+		goto fail;
+	}
+
+	if (!crypto_bignum_is_one(cofactor)) {
+		struct crypto_ec_point *point;
+		int ok = 1;
+
+		/* check to ensure peer's element is not in a small sub-group */
+		point = crypto_ec_point_init(group->group);
+		if (!point ||
+		    crypto_ec_point_mul(group->group, element,
+					cofactor, point) != 0 ||
+		    crypto_ec_point_is_at_infinity(group->group, point))
+			ok = 0;
+		crypto_ec_point_deinit(point, 0);
+
+		if (!ok) {
+			wpa_printf(MSG_INFO,
+				   "EAP-pwd: Small sub-group check on peer element failed");
+			goto fail;
+		}
+	}
+
+out:
+	crypto_bignum_deinit(cofactor, 0);
+	return element;
+fail:
+	crypto_ec_point_deinit(element, 0);
+	element = NULL;
+	goto out;
+}
+
+
+struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf)
+{
+	struct crypto_bignum *scalar;
+	const struct crypto_bignum *order;
+	size_t order_len;
+
+	order = crypto_ec_get_order(group->group);
+	order_len = crypto_ec_order_len(group->group);
+
+	/* RFC 5931, 2.8.5.2: 1 < scalar < r */
+	scalar = crypto_bignum_init_set(buf, order_len);
+	if (!scalar || crypto_bignum_is_zero(scalar) ||
+	    crypto_bignum_is_one(scalar) ||
+	    crypto_bignum_cmp(scalar, order) >= 0) {
+		wpa_printf(MSG_INFO, "EAP-pwd: received scalar is invalid");
+		crypto_bignum_deinit(scalar, 0);
+		scalar = NULL;
+	}
+
+	return scalar;
+}
diff --git a/src/eap_common/eap_pwd_common.h b/src/eap_common/eap_pwd_common.h
index a0d717e..01f43eb 100644
--- a/src/eap_common/eap_pwd_common.h
+++ b/src/eap_common/eap_pwd_common.h
@@ -68,5 +68,8 @@ int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, const BIGNUM *k,
 struct crypto_hash * eap_pwd_h_init(void);
 void eap_pwd_h_update(struct crypto_hash *hash, const u8 *data, size_t len);
 void eap_pwd_h_final(struct crypto_hash *hash, u8 *digest);
+struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
+					     const u8 *buf);
+struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf);
 
 #endif  /* EAP_PWD_COMMON_H */
diff --git a/src/eap_peer/eap_pwd.c b/src/eap_peer/eap_pwd.c
index d2bc981..bbe9b40 100644
--- a/src/eap_peer/eap_pwd.c
+++ b/src/eap_peer/eap_pwd.c
@@ -358,7 +358,7 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
 				const struct wpabuf *reqData,
 				const u8 *payload, size_t payload_len)
 {
-	EC_POINT *K = NULL, *point = NULL;
+	EC_POINT *K = NULL;
 	BIGNUM *mask = NULL, *x = NULL, *y = NULL, *cofactor = NULL;
 	u16 offset;
 	u8 *ptr, *scalar = NULL, *element = NULL;
@@ -429,7 +429,6 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
 	if (((data->server_scalar = BN_new()) == NULL) ||
 	    ((data->k = BN_new()) == NULL) ||
 	    ((K = EC_POINT_new(data->grp->group)) == NULL) ||
-	    ((point = EC_POINT_new(data->grp->group)) == NULL) ||
 	    ((data->server_element = EC_POINT_new(data->grp->group)) == NULL))
 	{
 		wpa_printf(MSG_INFO, "EAP-PWD (peer): peer data allocation "
@@ -452,21 +451,6 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
 		goto fin;
 	}
 
-	/* check to ensure server's element is not in a small sub-group */
-	if (BN_cmp(cofactor, BN_value_one())) {
-		if (!EC_POINT_mul(data->grp->group, point, NULL,
-				  data->server_element, cofactor, NULL)) {
-			wpa_printf(MSG_INFO, "EAP-PWD (peer): cannot multiply "
-				   "server element by order!\n");
-			goto fin;
-		}
-		if (EC_POINT_is_at_infinity(data->grp->group, point)) {
-			wpa_printf(MSG_INFO, "EAP-PWD (peer): server element "
-				   "is at infinity!\n");
-			goto fin;
-		}
-	}
-
 	/* compute the shared key, k */
 	if ((!EC_POINT_mul(data->grp->group, K, NULL, data->grp->pwe,
 			   data->server_scalar, data->bnctx)) ||
@@ -557,7 +541,6 @@ fin:
 	BN_clear_free(mask);
 	BN_clear_free(cofactor);
 	EC_POINT_clear_free(K);
-	EC_POINT_clear_free(point);
 	if (data->outbuf == NULL)
 		eap_pwd_state(data, FAILURE);
 	else
diff --git a/src/eap_server/eap_server_pwd.c b/src/eap_server/eap_server_pwd.c
index cb5f682..275bdf8 100644
--- a/src/eap_server/eap_server_pwd.c
+++ b/src/eap_server/eap_server_pwd.c
@@ -659,7 +659,7 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
 {
 	u8 *ptr;
 	BIGNUM *x = NULL, *y = NULL, *cofactor = NULL;
-	EC_POINT *K = NULL, *point = NULL;
+	EC_POINT *K = NULL;
 	int res = 0;
 	size_t prime_len, order_len;
 
@@ -681,7 +681,6 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
 	    ((cofactor = BN_new()) == NULL) ||
 	    ((x = BN_new()) == NULL) ||
 	    ((y = BN_new()) == NULL) ||
-	    ((point = EC_POINT_new(data->grp->group)) == NULL) ||
 	    ((K = EC_POINT_new(data->grp->group)) == NULL) ||
 	    ((data->peer_element = EC_POINT_new(data->grp->group)) == NULL)) {
 		wpa_printf(MSG_INFO, "EAP-PWD (server): peer data allocation "
@@ -710,21 +709,6 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
 		goto fin;
 	}
 
-	/* check to ensure peer's element is not in a small sub-group */
-	if (BN_cmp(cofactor, BN_value_one())) {
-		if (!EC_POINT_mul(data->grp->group, point, NULL,
-				  data->peer_element, cofactor, NULL)) {
-			wpa_printf(MSG_INFO, "EAP-PWD (server): cannot "
-				   "multiply peer element by order");
-			goto fin;
-		}
-		if (EC_POINT_is_at_infinity(data->grp->group, point)) {
-			wpa_printf(MSG_INFO, "EAP-PWD (server): peer element "
-				   "is at infinity!\n");
-			goto fin;
-		}
-	}
-
 	/* detect reflection attacks */
 	if (crypto_bignum_cmp(data->my_scalar, data->peer_scalar) == 0 ||
 	    crypto_ec_point_cmp(data->grp->group, data->my_element,
@@ -777,7 +761,6 @@ eap_pwd_process_commit_resp(struct eap_sm *sm, struct eap_pwd_data *data,
 
 fin:
 	EC_POINT_clear_free(K);
-	EC_POINT_clear_free(point);
 	BN_clear_free(cofactor);
 	BN_clear_free(x);
 	BN_clear_free(y);
-- 
2.19.1