Implement server certificate validation in smtp(1).

Check certificate against MX name in smtpd(8) mta.

ok gilles@

9 files changed, 396 insertions, 28 deletions

diff --git a/usr.sbin/smtpd/dns.c b/usr.sbin/smtpd/dns.c
index 4d369e2479f..d5b66af98ad 100644
--- a/usr.sbin/smtpd/dns.c
+++ b/usr.sbin/smtpd/dns.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: dns.c,v 1.88 2018/09/26 16:28:34 eric Exp $	*/
+/*	$OpenBSD: dns.c,v 1.89 2019/09/18 11:26:30 eric Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@poolp.org>
@@ -43,6 +43,7 @@
 
 struct dns_lookup {
 	struct dns_session	*session;
+	char			*host;
 	int			 preference;
 };
 
@@ -144,6 +145,7 @@ dns_imsg(struct mproc *p, struct imsg *imsg)
 		if (domainname_is_addr(domain, sa, &sl)) {
 			m_create(s->p, IMSG_MTA_DNS_HOST, 0, 0, -1);
 			m_add_id(s->p, s->reqid);
+			m_add_string(s->p, sockaddr_to_text(sa));
 			m_add_sockaddr(s->p, sa);
 			m_add_int(s->p, -1);
 			m_close(s->p);
@@ -208,10 +210,12 @@ dns_dispatch_host(struct asr_result *ar, void *arg)
 		s->mxfound++;
 		m_create(s->p, IMSG_MTA_DNS_HOST, 0, 0, -1);
 		m_add_id(s->p, s->reqid);
+		m_add_string(s->p, lookup->host);
 		m_add_sockaddr(s->p, ai->ai_addr);
 		m_add_int(s->p, lookup->preference);
 		m_close(s->p);
 	}
+	free(lookup->host);
 	free(lookup);
 	if (ar->ar_addrinfo)
 		freeaddrinfo(ar->ar_addrinfo);
@@ -338,6 +342,7 @@ dns_lookup_host(struct dns_session *s, const char *host, int preference)
 
 	lookup = xcalloc(1, sizeof *lookup);
 	lookup->preference = preference;
+	lookup->host = xstrdup(host);
 	lookup->session = s;
 	s->refcount++;
 
diff --git a/usr.sbin/smtpd/mta.c b/usr.sbin/smtpd/mta.c
index 1c60abd97d6..926b089a5f5 100644
--- a/usr.sbin/smtpd/mta.c
+++ b/usr.sbin/smtpd/mta.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mta.c,v 1.230 2019/09/14 06:20:27 gilles Exp $	*/
+/*	$OpenBSD: mta.c,v 1.231 2019/09/18 11:26:30 eric Exp $	*/
 
 /*
  * Copyright (c) 2008 Pierre-Yves Ritschard <pyr@openbsd.org>
@@ -76,7 +76,7 @@ static void mta_drain(struct mta_relay *);
 static void mta_delivery_flush_event(int, short, void *);
 static void mta_flush(struct mta_relay *, int, const char *);
 static struct mta_route *mta_find_route(struct mta_connector *, time_t, int*,
-    time_t*);
+    time_t*, struct mta_mx **);
 static void mta_log(const struct mta_envelope *, const char *, const char *,
     const char *, const char *);
 
@@ -255,11 +255,13 @@ mta_imsg(struct mproc *p, struct imsg *imsg)
 	case IMSG_MTA_DNS_HOST:
 		m_msg(&m, imsg);
 		m_get_id(&m, &reqid);
+		m_get_string(&m, &hostname);
 		m_get_sockaddr(&m, (struct sockaddr*)&ss);
 		m_get_int(&m, &preference);
 		m_end(&m);
 		domain = tree_xget(&wait_mx, reqid);
 		mx = xcalloc(1, sizeof *mx);
+		mx->mxname = xstrdup(hostname);
 		mx->host = mta_host((struct sockaddr*)&ss);
 		mx->preference = preference;
 		TAILQ_FOREACH(imx, &domain->mxs, entry) {
@@ -1146,6 +1148,7 @@ static void
 mta_connect(struct mta_connector *c)
 {
 	struct mta_route	*route;
+	struct mta_mx		*mx;
 	struct mta_limits	*l = c->relay->limits;
 	int			 limits;
 	time_t			 nextconn, now;
@@ -1234,7 +1237,7 @@ mta_connect(struct mta_connector *c)
 
 	/* We can connect now, find a route */
 	if (!limits && nextconn <= now)
-		route = mta_find_route(c, now, &limits, &nextconn);
+		route = mta_find_route(c, now, &limits, &nextconn, &mx);
 	else
 		route = NULL;
 
@@ -1281,7 +1284,7 @@ mta_connect(struct mta_connector *c)
 	route->dst->nconn += 1;
 	route->dst->lastconn = c->lastconn;
 
-	mta_session(c->relay, route);	/* this never fails synchronously */
+	mta_session(c->relay, route, mx->mxname);	/* this never fails synchronously */
 	mta_relay_ref(c->relay);
 
     goto again;
@@ -1510,7 +1513,7 @@ mta_flush(struct mta_relay *relay, int fail, const char *error)
  */
 static struct mta_route *
 mta_find_route(struct mta_connector *c, time_t now, int *limits,
-    time_t *nextconn)
+    time_t *nextconn, struct mta_mx **pmx)
 {
 	struct mta_route	*route, *best;
 	struct mta_limits	*l = c->relay->limits;
@@ -1654,6 +1657,7 @@ mta_find_route(struct mta_connector *c, time_t now, int *limits,
 		if (best)
 			mta_route_unref(best); /* from here */
 		best = route;
+		*pmx = mx;
 		log_debug("debug: mta-routing: selecting candidate route %s",
 		    mta_route_to_text(route));
 	}
@@ -2197,6 +2201,7 @@ mta_domain_unref(struct mta_domain *d)
 	while ((mx = TAILQ_FIRST(&d->mxs))) {
 		TAILQ_REMOVE(&d->mxs, mx, entry);
 		mta_host_unref(mx->host); /* from IMSG_DNS_HOST */
+		free(mx->mxname);
 		free(mx);
 	}
 
diff --git a/usr.sbin/smtpd/mta_session.c b/usr.sbin/smtpd/mta_session.c
index 1a668f126e6..f5366623d3f 100644
--- a/usr.sbin/smtpd/mta_session.c
+++ b/usr.sbin/smtpd/mta_session.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mta_session.c,v 1.120 2019/08/11 11:11:02 gilles Exp $	*/
+/*	$OpenBSD: mta_session.c,v 1.121 2019/09/18 11:26:30 eric Exp $	*/
 
 /*
  * Copyright (c) 2008 Pierre-Yves Ritschard <pyr@openbsd.org>
@@ -103,6 +103,7 @@ struct mta_session {
 	struct mta_relay	*relay;
 	struct mta_route	*route;
 	char			*helo;
+	char			*mxname;
 
 	int			 flags;
 
@@ -187,7 +188,7 @@ mta_session_init(void)
 }
 
 void
-mta_session(struct mta_relay *relay, struct mta_route *route)
+mta_session(struct mta_relay *relay, struct mta_route *route, const char *mxname)
 {
 	struct mta_session	*s;
 	struct timeval		 tv;
@@ -198,6 +199,7 @@ mta_session(struct mta_relay *relay, struct mta_route *route)
 	s->id = generate_uid();
 	s->relay = relay;
 	s->route = route;
+	s->mxname = xstrdup(mxname);
 
 	if (relay->flags & RELAY_LMTP)
 		s->flags |= MTA_LMTP;
@@ -366,6 +368,7 @@ mta_free(struct mta_session *s)
 
 	relay = s->relay;
 	route = s->route;
+	free(s->mxname);
 	free(s);
 	stat_decrement("mta.session", 1);
 	mta_route_collect(relay, route);
@@ -1521,13 +1524,27 @@ static void
 mta_cert_verify_cb(void *arg, int status)
 {
 	struct mta_session *s = arg;
-	int resume = 0;
+	int match, resume = 0;
+	X509 *cert;
 
 	if (s->flags & MTA_WAIT) {
 		mta_tree_pop(&wait_tls_verify, s->id);
 		resume = 1;
 	}
 
+	if (status == CERT_OK) {
+		cert = SSL_get_peer_certificate(io_tls(s->io));
+		if (!cert)
+			status = CERT_NOCERT;
+		else {
+			match = 0;
+			(void)ssl_check_name(cert, s->mxname, &match);
+			X509_free(cert);
+			if (!match)
+				status = CERT_INVALID;
+		}
+	}
+
 	if (status == CERT_OK)
 		s->flags |= MTA_TLS_VERIFIED;
 	else if (s->relay->flags & RELAY_TLS_VERIFY) {
diff --git a/usr.sbin/smtpd/smtp/Makefile b/usr.sbin/smtpd/smtp/Makefile
index 6708ab6e20d..fc47fa03935 100644
--- a/usr.sbin/smtpd/smtp/Makefile
+++ b/usr.sbin/smtpd/smtp/Makefile
@@ -1,4 +1,4 @@
-#	$OpenBSD: Makefile,v 1.2 2019/06/12 17:42:53 eric Exp $
+#	$OpenBSD: Makefile,v 1.3 2019/09/18 11:26:30 eric Exp $
 
 .PATH:	${.CURDIR}/..
 
@@ -13,7 +13,7 @@ SRCS+=	log.c
 SRCS+=	smtp_client.c
 SRCS+=	smtpc.c
 SRCS+=	ssl.c
-SRCS+=	ssl_smtpd.c
+SRCS+=	ssl_verify.c
 
 CPPFLAGS+= -DIO_TLS
 
diff --git a/usr.sbin/smtpd/smtpc.c b/usr.sbin/smtpd/smtpc.c
index 66be5fa389b..fb6d711d95f 100644
--- a/usr.sbin/smtpd/smtpc.c
+++ b/usr.sbin/smtpd/smtpc.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtpc.c,v 1.8 2019/09/02 20:05:21 eric Exp $	*/
+/*	$OpenBSD: smtpc.c,v 1.9 2019/09/18 11:26:30 eric Exp $	*/
 
 /*
  * Copyright (c) 2018 Eric Faurot <eric@openbsd.org>
@@ -20,6 +20,7 @@
 #include <sys/socket.h>
 
 #include <event.h>
+#include <limits.h>
 #include <netdb.h>
 #include <pwd.h>
 #include <resolv.h>
@@ -30,12 +31,12 @@
 #include <syslog.h>
 #include <unistd.h>
 
+#include <openssl/ssl.h>
+
 #include "smtp.h"
+#include "ssl.h"
 #include "log.h"
 
-void ssl_init(void);
-void *ssl_mta_init(void *, char *, off_t, const char *);
-
 static void parse_server(char *);
 static void parse_message(FILE *);
 static void resume(void);
@@ -46,6 +47,9 @@ static int noaction = 0;
 static struct addrinfo *res0, *ai;
 static struct smtp_params params;
 static struct smtp_mail mail;
+static const char *servname = NULL;
+
+static SSL_CTX *ssl_ctx;
 
 static void
 usage(void)
@@ -53,7 +57,7 @@ usage(void)
 	extern char *__progname;
 
 	fprintf(stderr,
-	    "usage: %s [-Chnv] [-F from] [-H helo] [-s server] rcpt ...\n",
+	    "usage: %s [-Chnv] [-F from] [-H helo] [-s server] [-S name] rcpt ...\n",
 	    __progname);
 	exit(1);
 }
@@ -87,7 +91,7 @@ main(int argc, char **argv)
 	memset(&mail, 0, sizeof(mail));
 	mail.from = pw->pw_name;
 
-	while ((ch = getopt(argc, argv, "CF:H:hns:v")) != -1) {
+	while ((ch = getopt(argc, argv, "CF:H:S:hns:v")) != -1) {
 		switch (ch) {
 		case 'C':
 			params.tls_verify = 0;
@@ -98,6 +102,9 @@ main(int argc, char **argv)
 		case 'H':
 			params.helo = optarg;
 			break;
+		case 'S':
+			servname = optarg;
+			break;
 		case 'h':
 			usage();
 			break;
@@ -132,6 +139,14 @@ main(int argc, char **argv)
 	ssl_init();
 	event_init();
 
+	ssl_ctx = ssl_ctx_create(NULL, NULL, 0, NULL);
+	if (!SSL_CTX_load_verify_locations(ssl_ctx,
+	    X509_get_default_cert_file(), NULL))
+		fatal("SSL_CTX_load_verify_locations");
+	if (!SSL_CTX_set_ssl_version(ssl_ctx, SSLv23_client_method()))
+		fatal("SSL_CTX_set_ssl_version");
+	SSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_NONE , NULL);
+
 	if (pledge("stdio inet dns tmppath", NULL) == -1)
 		fatal("pledge");
 
@@ -245,6 +260,9 @@ parse_server(char *server)
 	if (port == NULL)
 		port = "smtp";
 
+	if (servname == NULL)
+		servname = host;
+
 	memset(&hints, 0, sizeof(hints));
 	hints.ai_family = AF_UNSPEC;
 	hints.ai_socktype = SOCK_STREAM;
@@ -330,20 +348,42 @@ log_trace(int lvl, const char *emsg, ...)
 void
 smtp_verify_server_cert(void *tag, struct smtp_client *proto, void *ctx)
 {
-	log_debug("validating server certificate...");
+	SSL *ssl = ctx;
+	X509 *cert;
+	long res;
+	int r, match;
+
+	if ((cert = SSL_get_peer_certificate(ssl))) {
+		r = ssl_check_name(cert, servname, &match);
+		X509_free(cert);
+		res = SSL_get_verify_result(ssl);
+		if (res == X509_V_OK) {
+			if (match) {
+				log_debug("valid certificate");
+				smtp_cert_verified(proto, CERT_OK);
+			}
+			else {
+				log_debug("certificate does not match hostname");
+				smtp_cert_verified(proto, CERT_INVALID);
+			}
+			return;
+		}
+		log_debug("certificate validation error %ld", res);
+	}
+	else
+		log_debug("no certificate provided");
 
-	/* Not implemented for now. */
-	smtp_cert_verified(proto, CERT_UNKNOWN);
+	smtp_cert_verified(proto, CERT_INVALID);
 }
 
 void
 smtp_require_tls(void *tag, struct smtp_client *proto)
 {
-	void *ctx;
-
-	ctx = ssl_mta_init(NULL, NULL, 0, NULL);
+	SSL *ssl = NULL;
 
-	smtp_set_tls(proto, ctx);
+	if ((ssl = SSL_new(ssl_ctx)) == NULL)
+		fatal("SSL_new");
+	smtp_set_tls(proto, ssl);
 }
 
 void
diff --git a/usr.sbin/smtpd/smtpd.h b/usr.sbin/smtpd/smtpd.h
index 804b940d6e0..261c03008a1 100644
--- a/usr.sbin/smtpd/smtpd.h
+++ b/usr.sbin/smtpd/smtpd.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtpd.h,v 1.636 2019/09/11 04:19:19 martijn Exp $	*/
+/*	$OpenBSD: smtpd.h,v 1.637 2019/09/18 11:26:30 eric Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@poolp.org>
@@ -679,6 +679,7 @@ struct mta_host {
 struct mta_mx {
 	TAILQ_ENTRY(mta_mx)	 entry;
 	struct mta_host		*host;
+	char			*mxname;
 	int			 preference;
 };
 
@@ -1475,7 +1476,7 @@ const char *mta_relay_to_text(struct mta_relay *);
 
 
 /* mta_session.c */
-void mta_session(struct mta_relay *, struct mta_route *);
+void mta_session(struct mta_relay *, struct mta_route *, const char *);
 void mta_session_imsg(struct mproc *, struct imsg *);
 
 
diff --git a/usr.sbin/smtpd/smtpd/Makefile b/usr.sbin/smtpd/smtpd/Makefile
index d37ff4e3388..46e80c6a5ea 100644
--- a/usr.sbin/smtpd/smtpd/Makefile
+++ b/usr.sbin/smtpd/smtpd/Makefile
@@ -1,4 +1,4 @@
-#	$OpenBSD: Makefile,v 1.102 2019/08/10 16:07:02 gilles Exp $
+#	$OpenBSD: Makefile,v 1.103 2019/09/18 11:26:30 eric Exp $
 
 .PATH:		${.CURDIR}/..
 
@@ -52,6 +52,7 @@ SRCS+=	smtp_session.c
 SRCS+=	smtpd.c
 SRCS+=	ssl.c
 SRCS+=	ssl_smtpd.c
+SRCS+=	ssl_verify.c
 SRCS+=	stat_backend.c
 SRCS+=	table.c
 SRCS+=	to.c
diff --git a/usr.sbin/smtpd/ssl.h b/usr.sbin/smtpd/ssl.h
index dfa6994cdb8..1c0dc072d11 100644
--- a/usr.sbin/smtpd/ssl.h
+++ b/usr.sbin/smtpd/ssl.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ssl.h,v 1.20 2016/04/21 14:27:41 jsing Exp $	*/
+/*	$OpenBSD: ssl.h,v 1.21 2019/09/18 11:26:30 eric Exp $	*/
 /*
  * Copyright (c) 2013 Gilles Chehade <gilles@poolp.org>
  *
@@ -65,3 +65,6 @@ int		ssl_ctx_fake_private_key(SSL_CTX *, const void *, size_t,
 
 /* ssl_privsep.c */
 int		ssl_by_mem_ctrl(X509_LOOKUP *, int, const char *, long, char **);
+
+/* ssl_verify.c */
+int ssl_check_name(X509 *, const char *, int *);
diff --git a/usr.sbin/smtpd/ssl_verify.c b/usr.sbin/smtpd/ssl_verify.c
new file mode 100644
index 00000000000..ebc79870290
--- /dev/null
+++ b/usr.sbin/smtpd/ssl_verify.c
@@ -0,0 +1,296 @@
+/* $OpenBSD: ssl_verify.c,v 1.1 2019/09/18 11:26:30 eric Exp $ */
+/*
+ * Copyright (c) 2014 Jeremie Courreges-Anglas <jca@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* Adapted from lib/libtls/tls_verify.c */
+
+
+#include <sys/socket.h>
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+
+#include <limits.h>
+#include <string.h>
+
+#include <openssl/x509v3.h>
+
+#if 0
+#include <tls.h>
+#include "tls_internal.h"
+#endif
+
+#include "ssl.h"
+#include "log.h"
+
+struct tls;
+#define tls_set_errorx(ctx, ...) log_warnx(__VA_ARGS__)
+union tls_addr {
+	struct in_addr in;
+	struct in6_addr in6;
+};
+
+static int
+tls_match_name(const char *cert_name, const char *name)
+{
+	const char *cert_domain, *domain, *next_dot;
+
+	if (strcasecmp(cert_name, name) == 0)
+		return 0;
+
+	/* Wildcard match? */
+	if (cert_name[0] == '*') {
+		/*
+		 * Valid wildcards:
+		 * - "*.domain.tld"
+		 * - "*.sub.domain.tld"
+		 * - etc.
+		 * Reject "*.tld".
+		 * No attempt to prevent the use of eg. "*.co.uk".
+		 */
+		cert_domain = &cert_name[1];
+		/* Disallow "*"  */
+		if (cert_domain[0] == '\0')
+			return -1;
+		/* Disallow "*foo" */
+		if (cert_domain[0] != '.')
+			return -1;
+		/* Disallow "*.." */
+		if (cert_domain[1] == '.')
+			return -1;
+		next_dot = strchr(&cert_domain[1], '.');
+		/* Disallow "*.bar" */
+		if (next_dot == NULL)
+			return -1;
+		/* Disallow "*.bar.." */
+		if (next_dot[1] == '.')
+			return -1;
+
+		domain = strchr(name, '.');
+
+		/* No wildcard match against a name with no host part. */
+		if (name[0] == '.')
+			return -1;
+		/* No wildcard match against a name with no domain part. */
+		if (domain == NULL || strlen(domain) == 1)
+			return -1;
+
+		if (strcasecmp(cert_domain, domain) == 0)
+			return 0;
+	}
+
+	return -1;
+}
+
+/*
+ * See RFC 5280 section 4.2.1.6 for SubjectAltName details.
+ * alt_match is set to 1 if a matching alternate name is found.
+ * alt_exists is set to 1 if any known alternate name exists in the certificate.
+ */
+static int
+tls_check_subject_altname(struct tls *ctx, X509 *cert, const char *name,
+    int *alt_match, int *alt_exists)
+{
+	STACK_OF(GENERAL_NAME) *altname_stack = NULL;
+	union tls_addr addrbuf;
+	int addrlen, type;
+	int count, i;
+	int rv = 0;
+
+	*alt_match = 0;
+	*alt_exists = 0;
+
+	altname_stack = X509_get_ext_d2i(cert, NID_subject_alt_name,
+	    NULL, NULL);
+	if (altname_stack == NULL)
+		return 0;
+
+	if (inet_pton(AF_INET, name, &addrbuf) == 1) {
+		type = GEN_IPADD;
+		addrlen = 4;
+	} else if (inet_pton(AF_INET6, name, &addrbuf) == 1) {
+		type = GEN_IPADD;
+		addrlen = 16;
+	} else {
+		type = GEN_DNS;
+		addrlen = 0;
+	}
+
+	count = sk_GENERAL_NAME_num(altname_stack);
+	for (i = 0; i < count; i++) {
+		GENERAL_NAME	*altname;
+
+		altname = sk_GENERAL_NAME_value(altname_stack, i);
+
+		if (altname->type == GEN_DNS || altname->type == GEN_IPADD)
+			*alt_exists = 1;
+
+		if (altname->type != type)
+			continue;
+
+		if (type == GEN_DNS) {
+			unsigned char	*data;
+			int		 format, len;
+
+			format = ASN1_STRING_type(altname->d.dNSName);
+			if (format == V_ASN1_IA5STRING) {
+				data = ASN1_STRING_data(altname->d.dNSName);
+				len = ASN1_STRING_length(altname->d.dNSName);
+
+				if (len < 0 || (size_t)len != strlen(data)) {
+					tls_set_errorx(ctx,
+					    "error verifying name '%s': "
+					    "NUL byte in subjectAltName, "
+					    "probably a malicious certificate",
+					    name);
+					rv = -1;
+					break;
+				}
+
+				/*
+				 * Per RFC 5280 section 4.2.1.6:
+				 * " " is a legal domain name, but that
+				 * dNSName must be rejected.
+				 */
+				if (strcmp(data, " ") == 0) {
+					tls_set_errorx(ctx,
+					    "error verifying name '%s': "
+					    "a dNSName of \" \" must not be "
+					    "used", name);
+					rv = -1;
+					break;
+				}
+
+				if (tls_match_name(data, name) == 0) {
+					*alt_match = 1;
+					break;
+				}
+			} else {
+#ifdef DEBUG
+				fprintf(stdout, "%s: unhandled subjectAltName "
+				    "dNSName encoding (%d)\n", getprogname(),
+				    format);
+#endif
+			}
+
+		} else if (type == GEN_IPADD) {
+			unsigned char	*data;
+			int		 datalen;
+
+			datalen = ASN1_STRING_length(altname->d.iPAddress);
+			data = ASN1_STRING_data(altname->d.iPAddress);
+
+			if (datalen < 0) {
+				tls_set_errorx(ctx,
+				    "Unexpected negative length for an "
+				    "IP address: %d", datalen);
+				rv = -1;
+				break;
+			}
+
+			/*
+			 * Per RFC 5280 section 4.2.1.6:
+			 * IPv4 must use 4 octets and IPv6 must use 16 octets.
+			 */
+			if (datalen == addrlen &&
+			    memcmp(data, &addrbuf, addrlen) == 0) {
+				*alt_match = 1;
+				break;
+			}
+		}
+	}
+
+	sk_GENERAL_NAME_pop_free(altname_stack, GENERAL_NAME_free);
+	return rv;
+}
+
+static int
+tls_check_common_name(struct tls *ctx, X509 *cert, const char *name,
+    int *cn_match)
+{
+	X509_NAME *subject_name;
+	char *common_name = NULL;
+	union tls_addr addrbuf;
+	int common_name_len;
+	int rv = 0;
+
+	*cn_match = 0;
+
+	subject_name = X509_get_subject_name(cert);
+	if (subject_name == NULL)
+		goto done;
+
+	common_name_len = X509_NAME_get_text_by_NID(subject_name,
+	    NID_commonName, NULL, 0);
+	if (common_name_len < 0)
+		goto done;
+
+	common_name = calloc(common_name_len + 1, 1);
+	if (common_name == NULL)
+		goto done;
+
+	X509_NAME_get_text_by_NID(subject_name, NID_commonName, common_name,
+	    common_name_len + 1);
+
+	/* NUL bytes in CN? */
+	if (common_name_len < 0 ||
+	    (size_t)common_name_len != strlen(common_name)) {
+		tls_set_errorx(ctx, "error verifying name '%s': "
+		    "NUL byte in Common Name field, "
+		    "probably a malicious certificate", name);
+		rv = -1;
+		goto done;
+	}
+
+	/*
+	 * We don't want to attempt wildcard matching against IP addresses,
+	 * so perform a simple comparison here.
+	 */
+	if (inet_pton(AF_INET,  name, &addrbuf) == 1 ||
+	    inet_pton(AF_INET6, name, &addrbuf) == 1) {
+		if (strcmp(common_name, name) == 0)
+			*cn_match = 1;
+		goto done;
+	}
+
+	if (tls_match_name(common_name, name) == 0)
+		*cn_match = 1;
+
+ done:
+	free(common_name);
+	return rv;
+}
+
+int
+ssl_check_name(X509 *cert, const char *name, int *match)
+{
+	int alt_exists;
+
+	*match = 0;
+
+	if (tls_check_subject_altname(NULL, cert, name, match,
+	    &alt_exists) == -1)
+		return -1;
+
+	/*
+	 * As per RFC 6125 section 6.4.4, if any known alternate name existed
+	 * in the certificate, we do not attempt to match on the CN.
+	 */
+	if (*match || alt_exists)
+		return 0;
+
+	return tls_check_common_name(NULL, cert, name, match);
+}