From: Alan T. DeKok <aland@freeradius.org>
Date: Sun, 25 Jul 2021 19:30:40 +0000 (-0400)
Subject: do SNI on the server side.
X-Git-Tag: release_3_0_24~109
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0159e1f0682cb5280a84eb8db1772ffedbc88cf5;p=thirdparty%2Ffreeradius-server.git

do SNI on the server side.

And cache the name in TLS-Server-Name-Indication
---

diff --git a/doc/ChangeLog b/doc/ChangeLog
index 8fec499ed0..006fc8ddf4 100644
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@ -12,6 +12,9 @@ FreeRADIUS 3.0.24 Thu 10 Jun 2021 12:00:00 EDT urgency=low
 	  See raddb/certs/realms/README.md
 	* Add Server Name Indication (SNI) for outbound RadSec connections.
 	  See raddb/sites-available/tls, and the home server tls configuration.
+	* Support SNI for inbound RadSec connections.  Certificates will
+	  be loaded from "realm_dir" in the "tls" section.  SNI will be
+	  cached in the TLS-Server-Name-Indication attribute.
 
 	Bug fixes
 	* Fix crash in trustrouter module (#4115). Patch from Alejandro Perez
diff --git a/raddb/certs/realms/REAMDE.md b/raddb/certs/realms/REAMDE.md
index 87d22e69e6..f4dee04dc0 100644
--- a/raddb/certs/realms/REAMDE.md
+++ b/raddb/certs/realms/REAMDE.md
@@ -166,7 +166,32 @@ configuration in the server is for all TLS functionality, and not just
 EAP.
 
 This means that the server can accept RadSec connections, and then
-present different server certificates to different clients.  However,
-there is currently no standard way for RadSec clients to send a Server
-Name Indicator (SNI) as with HTTPS.  As a result, certificate
-selection has to be done on something else, such as source IP address.
+present different server certificates to different clients.
+
+For this functionality to work, the certificates for EAP and RadSec
+*should* be in separate directories.
+
+### Clients
+
+RadSec clients can set the SNI to send in the `tls` subsection of the
+`home_server` definition.  See `sites-available/tls` for examples.
+
+### Servers
+
+See the `realm_dir` configuration item in the `tls` subsection for the
+location of the server certificates.
+
+If the server receives an SNI for a realm it does not recognize, it
+will just use the default TLS configuration.
+
+If the realm is recognized (i.e. there is a file in
+`${realm_dir}/%{TLS-Server-Name-Indication}.pem`, then that certificate will be chosen, and
+present to the RadSec client.  If there is no such file, then the
+default TLS configuration is used.
+
+The current behavior is to _require_ that the server certificate is in
+a file which taken from
+`${realm_dir}/%{TLS-Server-Name-Indication}.pem`.  Only the
+`realm_dir` portion of the filename is configurable.  The SNI portion
+is taken from the TLS messages, and the `.pem` suffix is hard-coded in
+the source code.
diff --git a/share/dictionary.freeradius.internal b/share/dictionary.freeradius.internal
index 499634bd85..347e3e59f3 100644
--- a/share/dictionary.freeradius.internal
+++ b/share/dictionary.freeradius.internal
@@ -599,6 +599,8 @@ ATTRIBUTE	TLS-Session-Cipher-Suite		1948	string
 ATTRIBUTE	TLS-Session-Cert-File			1949	string
 ATTRIBUTE	TLS-Session-Cert-Private-Key-File	1950	string
 
+ATTRIBUTE	TLS-Server-Name-Indication		1951	string
+
 #
 #	Range:	1960-2099
 #		Free
diff --git a/src/main/listen.c b/src/main/listen.c
index c9c2722614..fc9af01f01 100644
--- a/src/main/listen.c
+++ b/src/main/listen.c
@@ -615,6 +615,68 @@ static int dual_tcp_recv(rad_listen_t *listener)
 	return 1;
 }
 
+typedef struct {
+	char const	*name;
+	SSL_CTX		*ctx;
+} fr_realm_ctx_t;		/* hack from tls. */
+
+static int tls_sni_callback(SSL *ssl, UNUSED int *al, void *arg)
+{
+	fr_tls_server_conf_t *conf = arg;
+	char const *name, *p;
+	int type;
+	fr_realm_ctx_t my_r, *r;
+	REQUEST *request;
+	char buffer[PATH_MAX];
+
+	/*
+	 *	No SNI, that's fine.
+	 */
+	type = SSL_get_servername_type(ssl);
+	if (type < 0) return SSL_TLSEXT_ERR_OK;
+
+	/*
+	 *	No realms configured, just use the default context.
+	 */
+	if (!conf->realms) return SSL_TLSEXT_ERR_OK;
+
+	name = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
+	if (!name) return SSL_TLSEXT_ERR_OK;
+
+	/*
+	 *	RFC Section 6066 Section 3 says that the names are
+	 *	ASCII, without a trailing dot.  i.e. punycode.
+	 */
+	for (p = name; *p != '\0'; p++) {
+		if (*p == '-') continue;
+		if (*p == '.') continue;
+		if ((*p >= 'A') && (*p <= 'Z')) continue;
+		if ((*p >= 'a') && (*p <= 'z')) continue;
+		if ((*p >= '0') && (*p <= '9')) continue;
+
+		/*
+		 *	Anything else, ignore it.
+		 */
+		return SSL_TLSEXT_ERR_OK;
+	}
+
+	snprintf(buffer, sizeof(buffer), "%s/%s.pem", conf->realm_dir, name);
+
+	my_r.name = buffer;
+	r = fr_hash_table_finddata(conf->realms, &my_r);
+	if (!r) return SSL_TLSEXT_ERR_OK;
+
+	/*
+	 *	Set an attribute saying which server has been selected.
+	 */
+	request = (REQUEST *)SSL_get_ex_data(ssl, FR_TLS_EX_INDEX_REQUEST);
+	if (request) {
+		(void) pair_make_config("TLS-Server-Name-Indication", name, T_OP_SET);
+	}
+
+	(void) SSL_set_SSL_CTX(ssl, r->ctx);
+	return SSL_TLSEXT_ERR_OK;
+}
 
 static int dual_tcp_accept(rad_listen_t *listener)
 {
@@ -770,6 +832,14 @@ static int dual_tcp_accept(rad_listen_t *listener)
 
 #ifdef WITH_TLS
 		if (this->tls) {
+			/*
+			 *	Set up SNI callback.  We don't do it
+			 *	in the main TLS code, because EAP
+			 *	doesn't need or use SNI.
+			 */
+			SSL_CTX_set_tlsext_servername_callback(this->tls->ctx, tls_sni_callback);
+			SSL_CTX_set_tlsext_servername_arg(this->tls->ctx, this->tls);
+
 			this->recv = dual_tls_recv;
 			this->send = dual_tls_send;
 		}