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-rw-r--r--smtpd/ssl_verify.c297
1 files changed, 297 insertions, 0 deletions
diff --git a/smtpd/ssl_verify.c b/smtpd/ssl_verify.c
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+/* $OpenBSD: ssl_verify.c,v 1.2 2019/11/02 03:16:45 gilles 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 "includes.h"
+
+#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) {
+ const unsigned char *data;
+ int format, len;
+
+ format = ASN1_STRING_type(altname->d.dNSName);
+ if (format == V_ASN1_IA5STRING) {
+ data = ASN1_STRING_get0_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) {
+ const unsigned char *data;
+ int datalen;
+
+ datalen = ASN1_STRING_length(altname->d.iPAddress);
+ data = ASN1_STRING_get0_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);
+}
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.