1 files changed, 280 insertions, 0 deletions
diff --git a/tls_verify.c b/tls_verify.c
new file mode 100644
index 0000000..acbe163
--- /dev/null
+++ b/tls_verify.c
@@ -0,0 +1,280 @@
+/* $OpenBSD: tls_verify.c,v 1.20 2018/02/05 00:52:24 jsing 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.
+ */
+
+#include <sys/socket.h>
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+
+#include <string.h>
+
+#include <openssl/x509v3.h>
+
+#include <tls.h>
+#include "tls_internal.h"
+
+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
+tls_check_name(struct tls *ctx, X509 *cert, const char *name, int *match)
+{
+	int alt_exists;
+
+	*match = 0;
+
+	if (tls_check_subject_altname(ctx, 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(ctx, cert, name, match);
+}