Adding RFC2818 compliance checks to axTLS. Completely new are the Sub…

…jectAltName checks. The peer CN field fallback is implemented matching the OpenSSL behaviour. VERIFYHOST 0 == 1.

lib/axtls.c

@@ -48,6 +48,65 @@
 /* The last #include file should be: */
 #include "memdebug.h"
 
+
+#define HOST_NOMATCH 0
+#define HOST_MATCH   1
+
+static int hostmatch(const char *hostname, const char *pattern)
+{
+  const char *pattern_label_end, *pattern_wildcard, *hostname_label_end;
+  int wildcard_enabled;
+  size_t prefixlen, suffixlen;
+  pattern_wildcard = strchr(pattern, '*');
+  if(pattern_wildcard == NULL) {
+    return Curl_raw_equal(pattern, hostname) ? HOST_MATCH : HOST_NOMATCH;
+  }
+  /* We require at least 2 dots in pattern to avoid too wide wildcard
+     match. */
+  wildcard_enabled = 1;
+  pattern_label_end = strchr(pattern, '.');
+  if(pattern_label_end == NULL || strchr(pattern_label_end+1, '.') == NULL ||
+     pattern_wildcard > pattern_label_end ||
+     Curl_raw_nequal(pattern, "xn--", 4)) {
+    wildcard_enabled = 0;
+  }
+  if(!wildcard_enabled) {
+    return Curl_raw_equal(pattern, hostname) ? HOST_MATCH : HOST_NOMATCH;
+  }
+  hostname_label_end = strchr(hostname, '.');
+  if(hostname_label_end == NULL ||
+     !Curl_raw_equal(pattern_label_end, hostname_label_end)) {
+    return HOST_NOMATCH;
+  }
+  /* The wildcard must match at least one character, so the left-most
+     label of the hostname is at least as large as the left-most label
+     of the pattern. */
+  if(hostname_label_end - hostname < pattern_label_end - pattern) {
+    return HOST_NOMATCH;
+  }
+  prefixlen = pattern_wildcard - pattern;
+  suffixlen = pattern_label_end - (pattern_wildcard+1);
+  return Curl_raw_nequal(pattern, hostname, prefixlen) &&
+    Curl_raw_nequal(pattern_wildcard+1, hostname_label_end - suffixlen,
+                    suffixlen) ?
+    HOST_MATCH : HOST_NOMATCH;
+}
+
+static int
+cert_hostcheck(const char *match_pattern, const char *hostname)
+{
+  if(!match_pattern || !*match_pattern ||
+      !hostname || !*hostname) /* sanity check */
+    return 0;
+
+  if(Curl_raw_equal(hostname, match_pattern)) /* trivial case */
+    return 1;
+
+  if(hostmatch(hostname,match_pattern) == HOST_MATCH)
+    return 1;
+  return 0;
+}
+
 /* SSL_read is opied from axTLS compat layer */
 static int SSL_read(SSL *ssl, void *buf, int num)
 {
@@ -150,7 +209,11 @@ Curl_axtls_connect(struct connectdata *conn,
   int i, ssl_fcn_return;
   const uint8_t *ssl_sessionid;
   size_t ssl_idsize;
-  const char *x509;
+  const char *peer_CN;
+  uint32_t dns_altname_index;
+  const char *dns_altname;
+  int8_t found_subject_alt_names = 0;
+  int8_t found_subject_alt_name_matching_conn = 0;
 
   /* Assuming users will not compile in custom key/cert to axTLS */
   uint32_t client_option = SSL_NO_DEFAULT_KEY|SSL_SERVER_VERIFY_LATER;
@@ -296,19 +359,60 @@ Curl_axtls_connect(struct connectdata *conn,
   /* Here, gtls.c does issuer verification. axTLS has no straightforward
    * equivalent, so omitting for now.*/
 
-  /* See if common name was set in server certificate */
-  x509 = ssl_get_cert_dn(ssl, SSL_X509_CERT_COMMON_NAME);
-  if(x509 == NULL)
-    infof(data, "error fetching CN from cert\n");
-
   /* Here, gtls.c does the following
    * 1) x509 hostname checking per RFC2818.  axTLS doesn't support this, but
-   *    it seems useful.  Omitting for now.
+   *    it seems useful. This is now implemented, by Oscar Koeroo
    * 2) checks cert validity based on time.  axTLS does this in ssl_verify_cert
    * 3) displays a bunch of cert information.  axTLS doesn't support most of
    *    this, but a couple fields are available.
    */
 
+
+  /* There is no (DNS) Altnames count in the version 1.4.8 API. There is a risk of an inifite loop */
+  for (dns_altname_index = 0; ; dns_altname_index++) {
+    dns_altname = ssl_get_cert_subject_alt_dnsname(ssl, dns_altname_index);
+    if (dns_altname == NULL) {
+      break;
+    }
+    found_subject_alt_names = 1;
+
+    infof(data, "\tComparing subject alt name DNS with hostname: %s <-> %s\n", dns_altname, conn->host.name);
+    if (cert_hostcheck(dns_altname, conn->host.name)) {
+      found_subject_alt_name_matching_conn = 1;
+      break;
+    }
+  }
+
+  /* RFC2818 checks */
+  if (found_subject_alt_names && !found_subject_alt_name_matching_conn) {
+    /* Break connection ! */
+    Curl_axtls_close(conn, sockindex);
+    failf(data, "\tsubjectAltName(s) do not match %s\n", conn->host.dispname);
+    return CURLE_PEER_FAILED_VERIFICATION;
+  }
+  else if (found_subject_alt_names == 0) {
+    /* Per RFC2818, when no Subject Alt Names were available, examine the peer CN as a legacy fallback */
+    peer_CN = ssl_get_cert_dn(ssl, SSL_X509_CERT_COMMON_NAME);
+    if(peer_CN == NULL) {
+      /* Similar behaviour to the OpenSSL interface */
+      Curl_axtls_close(conn, sockindex);
+      failf(data, "unable to obtain common name from peer certificate");
+      return CURLE_PEER_FAILED_VERIFICATION;
+    }
+    else {
+      if(!cert_hostcheck((const char *)peer_CN, conn->host.name)) {
+        if(data->set.ssl.verifyhost > 1) {
+          /* Break connection ! */
+          Curl_axtls_close(conn, sockindex);
+          failf(data, "\tcommon name \"%s\" does not match \"%s\"\n", peer_CN, conn->host.dispname);
+          return CURLE_PEER_FAILED_VERIFICATION;
+        }
+        else
+          infof(data, "\tcommon name \"%s\" does not match \"%s\"\n", peer_CN, conn->host.dispname);
+      }
+    }
+  }
+
   /* General housekeeping */
   conn->ssl[sockindex].state = ssl_connection_complete;
   conn->ssl[sockindex].ssl = ssl;