From f77ecf0728f6e7a71e61afe78c7849dec6cce9e9 Mon Sep 17 00:00:00 2001
From: Tobias Brunner <tobias@strongswan.org>
Date: Thu, 11 Feb 2021 17:46:17 +0100
Subject: [PATCH] tls-crypto: Fallback to any supported ECDH group

If the default group listed in the cipher suite is not supported, we try
to use any other supported group (the groups are negotiated separately
so we are not locked in to a specific group).
---
 src/libtls/tls_crypto.c | 58 ++++++++++++++++++++++++++++++++---------
 1 file changed, 45 insertions(+), 13 deletions(-)

diff --git a/src/libtls/tls_crypto.c b/src/libtls/tls_crypto.c
index d7faa4e25..ed1eea36b 100644
--- a/src/libtls/tls_crypto.c
+++ b/src/libtls/tls_crypto.c
@@ -1418,19 +1418,6 @@ METHOD(tls_crypto_t, select_cipher_suite, tls_cipher_suite_t,
 	return 0;
 }
 
-METHOD(tls_crypto_t, get_dh_group, diffie_hellman_group_t,
-	private_tls_crypto_t *this)
-{
-	suite_algs_t *algs;
-
-	algs = find_suite(this->suite);
-	if (algs)
-	{
-		return algs->dh;
-	}
-	return MODP_NONE;
-}
-
 /**
  * Parameters for RSA/PSS signature schemes
  */
@@ -1629,6 +1616,7 @@ CALLBACK(config_filter, bool,
 	while (orig->enumerate(orig, &group, &curve))
 	{
 		if (filter_curve_config(curve))
+
 		{
 			if (group_out)
 			{
@@ -1654,6 +1642,50 @@ METHOD(tls_crypto_t, create_ec_enumerator, enumerator_t*,
 							config_filter, NULL, NULL);
 }
 
+/**
+ * Check if the given ECDH group is supported or return the first one we
+ * actually do support.
+ */
+static diffie_hellman_group_t supported_ec_group(private_tls_crypto_t *this,
+												 diffie_hellman_group_t orig)
+{
+	diffie_hellman_group_t current, first = MODP_NONE;
+	enumerator_t *enumerator;
+
+	enumerator = create_ec_enumerator(this);
+	while (enumerator->enumerate(enumerator, &current, NULL))
+	{
+		if (current == orig)
+		{
+			enumerator->destroy(enumerator);
+			return orig;
+		}
+		else if (first == MODP_NONE)
+		{
+			first = current;
+		}
+	}
+	enumerator->destroy(enumerator);
+	return first;
+}
+
+METHOD(tls_crypto_t, get_dh_group, diffie_hellman_group_t,
+	private_tls_crypto_t *this)
+{
+	suite_algs_t *algs;
+
+	algs = find_suite(this->suite);
+	if (algs)
+	{
+		if (diffie_hellman_group_is_ec(algs->dh))
+		{
+			return supported_ec_group(this, algs->dh);
+		}
+		return algs->dh;
+	}
+	return MODP_NONE;
+}
+
 METHOD(tls_crypto_t, set_protection, void,
 	private_tls_crypto_t *this, tls_protection_t *protection)
 {