ssluse.c

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2005, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at http://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * $Id$
 ***************************************************************************/

/*
 * Source file for all OpenSSL-specific code for the TLS/SSL layer. No code
 * but sslgen.c should ever call or use these functions.
 */

/*
 * The original SSLeay-using code for curl was written by Linas Vepstas and
 * Sampo Kellomaki 1998.
 */

#include "setup.h"

#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif

#include "urldata.h"
#include "sendf.h"
#include "formdata.h" /* for the boundary function */
#include "url.h" /* for the ssl config check function */
#include "inet_pton.h"
#include "ssluse.h"
#include "connect.h" /* Curl_ourerrno() proto */
#include "strequal.h"
#include "select.h"
#include "sslgen.h"

#define _MPRINTF_REPLACE /* use the internal *printf() functions */
#include <curl/mprintf.h>

#ifdef USE_SSLEAY

#ifdef USE_OPENSSL
#include <openssl/rand.h>
#include <openssl/x509v3.h>
#else
#include <rand.h>
#include <x509v3.h>
#endif

#include "memory.h"

/* The last #include file should be: */
#include "memdebug.h"

#ifndef min
#define min(a, b)   ((a) < (b) ? (a) : (b))
#endif

#if OPENSSL_VERSION_NUMBER >= 0x0090581fL
#define HAVE_SSL_GET1_SESSION 1
#else
#undef HAVE_SSL_GET1_SESSION
#endif

#if OPENSSL_VERSION_NUMBER >= 0x00904100L
#define HAVE_USERDATA_IN_PWD_CALLBACK 1
#else
#undef HAVE_USERDATA_IN_PWD_CALLBACK
#endif

#if OPENSSL_VERSION_NUMBER >= 0x00907001L
/* ENGINE_load_private_key() takes four arguments */
#define HAVE_ENGINE_LOAD_FOUR_ARGS
#else
/* ENGINE_load_private_key() takes three arguments */
#undef HAVE_ENGINE_LOAD_FOUR_ARGS
#endif

#if (OPENSSL_VERSION_NUMBER >= 0x00903001L) && defined(HAVE_OPENSSL_PKCS12_H)
/* OpenSSL has PKCS 12 support */
#define HAVE_PKCS12_SUPPORT
#else
/* OpenSSL/SSLEay does not have PKCS12 support */
#undef HAVE_PKCS12_SUPPORT
#endif


#if OPENSSL_VERSION_NUMBER >= 0x00906001L
#define HAVE_ERR_ERROR_STRING_N 1
#endif

/*
 * Number of bytes to read from the random number seed file. This must be
 * a finite value (because some entropy "files" like /dev/urandom have
 * an infinite length), but must be large enough to provide enough
 * entopy to properly seed OpenSSL's PRNG.
 */
#define RAND_LOAD_LENGTH 1024

#ifndef HAVE_USERDATA_IN_PWD_CALLBACK
static char global_passwd[64];
#endif

static int passwd_callback(char *buf, int num, int verify
#if HAVE_USERDATA_IN_PWD_CALLBACK
                           /* This was introduced in 0.9.4, we can set this
                              using SSL_CTX_set_default_passwd_cb_userdata()
                              */
                           , void *global_passwd
#endif
                           )
{
  if(verify)
    fprintf(stderr, "%s\n", buf);
  else {
    if(num > (int)strlen((char *)global_passwd)) {
      strcpy(buf, global_passwd);
      return (int)strlen(buf);
    }
  }
  return 0;
}

/*
 * rand_enough() is a function that returns TRUE if we have seeded the random
 * engine properly. We use some preprocessor magic to provide a seed_enough()
 * macro to use, just to prevent a compiler warning on this function if we
 * pass in an argument that is never used.
 */

#ifdef HAVE_RAND_STATUS
#define seed_enough(x) rand_enough()
static bool rand_enough(void)
{
  return RAND_status()?TRUE:FALSE;
}
#else
#define seed_enough(x) rand_enough(x)
static bool rand_enough(int nread)
{
  /* this is a very silly decision to make */
  return (nread > 500)?TRUE:FALSE;
}
#endif

static
int random_the_seed(struct SessionHandle *data)
{
  char *buf = data->state.buffer; /* point to the big buffer */
  int nread=0;

  /* Q: should we add support for a random file name as a libcurl option?
     A: Yes, it is here */

#ifndef RANDOM_FILE
  /* if RANDOM_FILE isn't defined, we only perform this if an option tells
     us to! */
  if(data->set.ssl.random_file)
#define RANDOM_FILE "" /* doesn't matter won't be used */
#endif
  {
    /* let the option override the define */
    nread += RAND_load_file((data->set.ssl.random_file?
                             data->set.ssl.random_file:RANDOM_FILE),
                            RAND_LOAD_LENGTH);
    if(seed_enough(nread))
      return nread;
  }

#if defined(HAVE_RAND_EGD)
  /* only available in OpenSSL 0.9.5 and later */
  /* EGD_SOCKET is set at configure time or not at all */
#ifndef EGD_SOCKET
  /* If we don't have the define set, we only do this if the egd-option
     is set */
  if(data->set.ssl.egdsocket)
#define EGD_SOCKET "" /* doesn't matter won't be used */
#endif
  {
    /* If there's an option and a define, the option overrides the
       define */
    int ret = RAND_egd(data->set.ssl.egdsocket?
                       data->set.ssl.egdsocket:EGD_SOCKET);
    if(-1 != ret) {
      nread += ret;
      if(seed_enough(nread))
        return nread;
    }
  }
#endif

  /* If we get here, it means we need to seed the PRNG using a "silly"
     approach! */
#ifdef HAVE_RAND_SCREEN
  /* This one gets a random value by reading the currently shown screen */
  RAND_screen();
  nread = 100; /* just a value */
#else
  {
    int len;
    char *area;

    /* Changed call to RAND_seed to use the underlying RAND_add implementation
     * directly.  Do this in a loop, with the amount of additional entropy
     * being dependent upon the algorithm used by Curl_FormBoundary(): N bytes
     * of a 7-bit ascii set. -- Richard Gorton, March 11 2003.
     */

    do {
      area = Curl_FormBoundary();
      if(!area)
        return 3; /* out of memory */

      len = (int)strlen(area);
      RAND_add(area, len, (len >> 1));

      free(area); /* now remove the random junk */
    } while (!RAND_status());
  }
#endif

  /* generates a default path for the random seed file */
  buf[0]=0; /* blank it first */
  RAND_file_name(buf, BUFSIZE);
  if(buf[0]) {
    /* we got a file name to try */
    nread += RAND_load_file(buf, RAND_LOAD_LENGTH);
    if(seed_enough(nread))
      return nread;
  }

  infof(data, "libcurl is now using a weak random seed!\n");
  return nread;
}

#ifndef SSL_FILETYPE_ENGINE
#define SSL_FILETYPE_ENGINE 42
#endif
#ifndef SSL_FILETYPE_PKCS12
#define SSL_FILETYPE_PKCS12 43
#endif
static int do_file_type(const char *type)
{
  if(!type || !type[0])
    return SSL_FILETYPE_PEM;
  if(curl_strequal(type, "PEM"))
    return SSL_FILETYPE_PEM;
  if(curl_strequal(type, "DER"))
    return SSL_FILETYPE_ASN1;
  if(curl_strequal(type, "ENG"))
    return SSL_FILETYPE_ENGINE;
  if(curl_strequal(type, "P12"))
    return SSL_FILETYPE_PKCS12;
  return -1;
}

static
int cert_stuff(struct connectdata *conn,
               SSL_CTX* ctx,
               char *cert_file,
               const char *cert_type,
               char *key_file,
               const char *key_type)
{
  struct SessionHandle *data = conn->data;
  int file_type;

  if(cert_file != NULL) {
    SSL *ssl;
    X509 *x509;
    int cert_done = 0;

    if(data->set.key_passwd) {
#ifndef HAVE_USERDATA_IN_PWD_CALLBACK
      /*
       * If password has been given, we store that in the global
       * area (*shudder*) for a while:
       */
      size_t len = strlen(data->set.key_passwd);
      if(len < sizeof(global_passwd))
        memcpy(global_passwd, data->set.key_passwd, len+1);
#else
      /*
       * We set the password in the callback userdata
       */
      SSL_CTX_set_default_passwd_cb_userdata(ctx,
                                             data->set.key_passwd);
#endif
      /* Set passwd callback: */
      SSL_CTX_set_default_passwd_cb(ctx, passwd_callback);
    }

    file_type = do_file_type(cert_type);

#define SSL_CLIENT_CERT_ERR \
    "unable to use client certificate (no key found or wrong pass phrase?)"

    switch(file_type) {
    case SSL_FILETYPE_PEM:
      /* SSL_CTX_use_certificate_chain_file() only works on PEM files */
      if(SSL_CTX_use_certificate_chain_file(ctx,
                                            cert_file) != 1) {
        failf(data, SSL_CLIENT_CERT_ERR);
        return 0;
      }
      break;

    case SSL_FILETYPE_ASN1:
      /* SSL_CTX_use_certificate_file() works with either PEM or ASN1, but
         we use the case above for PEM so this can only be performed with
         ASN1 files. */
      if(SSL_CTX_use_certificate_file(ctx,
                                      cert_file,
                                      file_type) != 1) {
        failf(data, SSL_CLIENT_CERT_ERR);
        return 0;
      }
      break;
    case SSL_FILETYPE_ENGINE:
      failf(data, "file type ENG for certificate not implemented");
      return 0;

    case SSL_FILETYPE_PKCS12:
    {
#ifdef HAVE_PKCS12_SUPPORT
      FILE *f;
      PKCS12 *p12;
      EVP_PKEY *pri;

      f = fopen(cert_file,"rb");
      if (!f) {
        failf(data, "could not open PKCS12 file '%s'", cert_file);
        return 0;
      }
      p12 = d2i_PKCS12_fp(f, NULL);
      fclose(f);

      PKCS12_PBE_add();

      if (!PKCS12_parse(p12, data->set.key_passwd, &pri, &x509, NULL)) {
        failf(data,
              "could not parse PKCS12 file, check password, OpenSSL error %s",
              ERR_error_string(ERR_get_error(), NULL) );
        return 0;
      }

      PKCS12_free(p12);

      if(SSL_CTX_use_certificate(ctx, x509) != 1) {
        failf(data, SSL_CLIENT_CERT_ERR);
        EVP_PKEY_free(pri);
        X509_free(x509);
        return 0;
      }

      if(SSL_CTX_use_PrivateKey(ctx, pri) != 1) {
        failf(data, "unable to use private key from PKCS12 file '%s'",
              cert_file);
        EVP_PKEY_free(pri);
        X509_free(x509);
        return 0;
      }

      EVP_PKEY_free(pri);
      X509_free(x509);
      cert_done = 1;
      break;
#else
      failf(data, "file type P12 for certificate not supported");
      return 0;
#endif
    }
    default:
      failf(data, "not supported file type '%s' for certificate", cert_type);
      return 0;
    }

    file_type = do_file_type(key_type);

    switch(file_type) {
    case SSL_FILETYPE_PEM:
      if(cert_done)
        break;
      if(key_file == NULL)
        /* cert & key can only be in PEM case in the same file */
        key_file=cert_file;
    case SSL_FILETYPE_ASN1:
      if(SSL_CTX_use_PrivateKey_file(ctx, key_file, file_type) != 1) {
        failf(data, "unable to set private key file: '%s' type %s\n",
              key_file, key_type?key_type:"PEM");
        return 0;
      }
      break;
    case SSL_FILETYPE_ENGINE:
#ifdef HAVE_OPENSSL_ENGINE_H
      {                         /* XXXX still needs some work */
        EVP_PKEY *priv_key = NULL;
        if(conn && conn->data && conn->data->state.engine) {
#ifdef HAVE_ENGINE_LOAD_FOUR_ARGS
          UI_METHOD *ui_method = UI_OpenSSL();
#endif
          if(!key_file || !key_file[0]) {
            failf(data, "no key set to load from crypto engine\n");
            return 0;
          }
          /* the typecast below was added to please mingw32 */
          priv_key = (EVP_PKEY *)
            ENGINE_load_private_key(conn->data->state.engine,key_file,
#ifdef HAVE_ENGINE_LOAD_FOUR_ARGS
                                    ui_method,
#endif
                                    data->set.key_passwd);
          if(!priv_key) {
            failf(data, "failed to load private key from crypto engine\n");
            return 0;
          }
          if(SSL_CTX_use_PrivateKey(ctx, priv_key) != 1) {
            failf(data, "unable to set private key\n");
            EVP_PKEY_free(priv_key);
            return 0;
          }
          EVP_PKEY_free(priv_key);  /* we don't need the handle any more... */
        }
        else {
          failf(data, "crypto engine not set, can't load private key\n");
          return 0;
        }
      }
      break;
#else
      failf(data, "file type ENG for private key not supported\n");
      return 0;
#endif
    case SSL_FILETYPE_PKCS12:
      if(!cert_done) {
        failf(data, "file type P12 for private key not supported\n");
        return 0;
      }
      break;
    default:
      failf(data, "not supported file type for private key\n");
      return 0;
    }

    ssl=SSL_new(ctx);
    if (NULL == ssl) {
      failf(data,"unable to create an SSL structure\n");
      return 0;
    }

    x509=SSL_get_certificate(ssl);

    /* This version was provided by Evan Jordan and is supposed to not
       leak memory as the previous version: */
    if(x509 != NULL) {
      EVP_PKEY *pktmp = X509_get_pubkey(x509);
      EVP_PKEY_copy_parameters(pktmp,SSL_get_privatekey(ssl));
      EVP_PKEY_free(pktmp);
    }

    SSL_free(ssl);

    /* If we are using DSA, we can copy the parameters from
     * the private key */


    /* Now we know that a key and cert have been set against
     * the SSL context */
    if(!SSL_CTX_check_private_key(ctx)) {
      failf(data, "Private key does not match the certificate public key");
      return(0);
    }
#ifndef HAVE_USERDATA_IN_PWD_CALLBACK
    /* erase it now */
    memset(global_passwd, 0, sizeof(global_passwd));
#endif
  }
  return(1);
}

static
int cert_verify_callback(int ok, X509_STORE_CTX *ctx)
{
  X509 *err_cert;
  char buf[256];

  err_cert=X509_STORE_CTX_get_current_cert(ctx);
  X509_NAME_oneline(X509_get_subject_name(err_cert), buf, sizeof(buf));
  return ok;
}

/* Return error string for last OpenSSL error
 */
static char *SSL_strerror(unsigned long error, char *buf, size_t size)
{
#ifdef HAVE_ERR_ERROR_STRING_N
  /* OpenSSL 0.9.6 and later has a function named
     ERRO_error_string_n() that takes the size of the buffer as a
     third argument */
  ERR_error_string_n(error, buf, size);
#else
  (void) size;
  ERR_error_string(error, buf);
#endif
  return (buf);
}

/* we have the "SSL is seeded" boolean global for the application to
   prevent multiple time-consuming seedings in vain */
static bool ssl_seeded = FALSE;
#endif /* USE_SSLEAY */

#ifdef USE_SSLEAY
/**
 * Global SSL init
 *
 * @retval 0 error initializing SSL
 * @retval 1 SSL initialized successfully
 */
int Curl_ossl_init(void)
{
#ifdef HAVE_ENGINE_LOAD_BUILTIN_ENGINES
  ENGINE_load_builtin_engines();
#endif

  /* Lets get nice error messages */
  SSL_load_error_strings();

  /* Setup all the global SSL stuff */
  if (!SSLeay_add_ssl_algorithms())
    return 0;

  return 1;
}

#endif /* USE_SSLEAY */

#ifdef USE_SSLEAY

/* Global cleanup */
void Curl_ossl_cleanup(void)
{
  /* Free the SSL error strings */
  ERR_free_strings();

  /* EVP_cleanup() removes all ciphers and digests from the
     table. */
  EVP_cleanup();

#ifdef HAVE_ENGINE_cleanup
  ENGINE_cleanup();
#endif

#ifdef HAVE_CRYPTO_CLEANUP_ALL_EX_DATA
  /* this function was not present in 0.9.6b, but was added sometimes
     later */
  CRYPTO_cleanup_all_ex_data();
#endif
}

#endif /* USE_SSLEAY */

/* Selects an OpenSSL crypto engine
 */
CURLcode Curl_ossl_set_engine(struct SessionHandle *data, const char *engine)
{
#if defined(USE_SSLEAY) && defined(HAVE_OPENSSL_ENGINE_H)
  ENGINE *e = ENGINE_by_id(engine);

  if (!e) {
    failf(data, "SSL Engine '%s' not found", engine);
    return (CURLE_SSL_ENGINE_NOTFOUND);
  }

  if (data->state.engine) {
    ENGINE_finish(data->state.engine);
    ENGINE_free(data->state.engine);
  }
  data->state.engine = NULL;
  if (!ENGINE_init(e)) {
    char buf[256];

    ENGINE_free(e);
    failf(data, "Failed to initialise SSL Engine '%s':\n%s",
          engine, SSL_strerror(ERR_get_error(), buf, sizeof(buf)));
    return (CURLE_SSL_ENGINE_INITFAILED);
  }
  data->state.engine = e;
  return (CURLE_OK);
#else
  (void)engine;
  failf(data, "SSL Engine not supported");
  return (CURLE_SSL_ENGINE_NOTFOUND);
#endif
}

#ifdef USE_SSLEAY
/* Sets engine as default for all SSL operations
 */
CURLcode Curl_ossl_set_engine_default(struct SessionHandle *data)
{
#ifdef HAVE_OPENSSL_ENGINE_H
  if (data->state.engine) {
    if (ENGINE_set_default(data->state.engine, ENGINE_METHOD_ALL) > 0) {
      infof(data,"set default crypto engine %s\n", data->state.engine);
    }
    else {
      failf(data, "set default crypto engine %s failed", data->state.engine);
      return CURLE_SSL_ENGINE_SETFAILED;
    }
  }
#else
  (void) data;
#endif
  return CURLE_OK;
}
#endif /* USE_SSLEAY */

/* Return list of OpenSSL crypto engine names.
 */
struct curl_slist *Curl_ossl_engines_list(struct SessionHandle *data)
{
  struct curl_slist *list = NULL;
#if defined(USE_SSLEAY) && defined(HAVE_OPENSSL_ENGINE_H)
  ENGINE *e;

  for (e = ENGINE_get_first(); e; e = ENGINE_get_next(e))
    list = curl_slist_append(list, ENGINE_get_id(e));
#endif
  (void) data;
  return (list);
}


#ifdef USE_SSLEAY

/*
 * This function is called when an SSL connection is closed.
 */
void Curl_ossl_close(struct connectdata *conn)
{
  int i;
  /*
    ERR_remove_state() frees the error queue associated with
    thread pid.  If pid == 0, the current thread will have its
    error queue removed.

    Since error queue data structures are allocated
    automatically for new threads, they must be freed when
    threads are terminated in oder to avoid memory leaks.
  */
  ERR_remove_state(0);

  for(i=0; i<2; i++) {
    struct ssl_connect_data *connssl = &conn->ssl[i];

    if(connssl->handle) {
      (void)SSL_shutdown(connssl->handle);
      SSL_set_connect_state(connssl->handle);

      SSL_free (connssl->handle);
      connssl->handle = NULL;
    }
    if(connssl->ctx) {
      SSL_CTX_free (connssl->ctx);
      connssl->ctx = NULL;
    }
    connssl->use = FALSE; /* get back to ordinary socket usage */
  }
}

void Curl_ossl_session_free(void *ptr)
{
  /* free the ID */
  SSL_SESSION_free(ptr);
}

/*
 * This function is called when the 'data' struct is going away. Close
 * down everything and free all resources!
 */
int Curl_ossl_close_all(struct SessionHandle *data)
{
#ifdef HAVE_OPENSSL_ENGINE_H
  if(data->state.engine) {
    ENGINE_finish(data->state.engine);
    ENGINE_free(data->state.engine);
    data->state.engine = NULL;
  }
#else
  (void)data;
#endif
  return 0;
}

static int Curl_ASN1_UTCTIME_output(struct connectdata *conn,
                                    const char *prefix,
                                    ASN1_UTCTIME *tm)
{
  char *asn1_string;
  int gmt=FALSE;
  int i;
  int year=0,month=0,day=0,hour=0,minute=0,second=0;
  struct SessionHandle *data = conn->data;

  if(!data->set.verbose)
    return 0;

  i=tm->length;
  asn1_string=(char *)tm->data;

  if(i < 10)
    return 1;
  if(asn1_string[i-1] == 'Z')
    gmt=TRUE;
  for (i=0; i<10; i++)
    if((asn1_string[i] > '9') || (asn1_string[i] < '0'))
      return 2;

  year= (asn1_string[0]-'0')*10+(asn1_string[1]-'0');
  if(year < 50)
    year+=100;

  month= (asn1_string[2]-'0')*10+(asn1_string[3]-'0');
  if((month > 12) || (month < 1))
    return 3;

  day= (asn1_string[4]-'0')*10+(asn1_string[5]-'0');
  hour= (asn1_string[6]-'0')*10+(asn1_string[7]-'0');
  minute=  (asn1_string[8]-'0')*10+(asn1_string[9]-'0');

  if((asn1_string[10] >= '0') && (asn1_string[10] <= '9') &&
     (asn1_string[11] >= '0') && (asn1_string[11] <= '9'))
    second= (asn1_string[10]-'0')*10+(asn1_string[11]-'0');

  infof(data,
        "%s%04d-%02d-%02d %02d:%02d:%02d %s\n",
        prefix, year+1900, month, day, hour, minute, second, (gmt?"GMT":""));

  return 0;
}

#endif

/* ====================================================== */
#ifdef USE_SSLEAY

/*
 * Match a hostname against a wildcard pattern.
 * E.g.
 *  "foo.host.com" matches "*.host.com".
 *
 * We are a bit more liberal than RFC2818 describes in that we
 * accept multiple "*" in pattern (similar to what some other browsers do).
 * E.g.
 *  "abc.def.domain.com" should strickly not match "*.domain.com", but we
 *  don't consider "." to be important in CERT checking.
 */
#define HOST_NOMATCH 0
#define HOST_MATCH   1

static int hostmatch(const char *hostname, const char *pattern)
{
  while (1) {
    int c = *pattern++;

    if (c == '\0')
      return (*hostname ? HOST_NOMATCH : HOST_MATCH);

    if (c == '*') {
      c = *pattern;
      if (c == '\0')      /* "*\0" matches anything remaining */
        return HOST_MATCH;

      while (*hostname) {
        /* The only recursive function in libcurl! */
        if (hostmatch(hostname++,pattern) == HOST_MATCH)
          return HOST_MATCH;
      }
      return HOST_NOMATCH;
    }

    if (toupper(c) != toupper(*hostname++))
      return 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_strequal(hostname,match_pattern)) /* trivial case */
    return 1;

  if (hostmatch(hostname,match_pattern) == HOST_MATCH)
    return 1;
  return 0;
}

/* Quote from RFC2818 section 3.1 "Server Identity"

   If a subjectAltName extension of type dNSName is present, that MUST
   be used as the identity. Otherwise, the (most specific) Common Name
   field in the Subject field of the certificate MUST be used. Although
   the use of the Common Name is existing practice, it is deprecated and
   Certification Authorities are encouraged to use the dNSName instead.

   Matching is performed using the matching rules specified by
   [RFC2459].  If more than one identity of a given type is present in
   the certificate (e.g., more than one dNSName name, a match in any one
   of the set is considered acceptable.) Names may contain the wildcard
   character * which is considered to match any single domain name
   component or component fragment. E.g., *.a.com matches foo.a.com but
   not bar.foo.a.com. f*.com matches foo.com but not bar.com.

   In some cases, the URI is specified as an IP address rather than a
   hostname. In this case, the iPAddress subjectAltName must be present
   in the certificate and must exactly match the IP in the URI.

*/
static CURLcode verifyhost(struct connectdata *conn,
                           X509 *server_cert)
{
  bool matched = FALSE; /* no alternative match yet */
  int target = GEN_DNS; /* target type, GEN_DNS or GEN_IPADD */
  int addrlen = 0;
  struct SessionHandle *data = conn->data;
  STACK_OF(GENERAL_NAME) *altnames;
#ifdef ENABLE_IPV6
  struct in6_addr addr;
#else
  struct in_addr addr;
#endif
  CURLcode res = CURLE_OK;

#ifdef ENABLE_IPV6
  if(conn->bits.ipv6_ip &&
     Curl_inet_pton(AF_INET6, conn->host.name, &addr)) {
    target = GEN_IPADD;
    addrlen = sizeof(struct in6_addr);
  }
  else
#endif
    if(Curl_inet_pton(AF_INET, conn->host.name, &addr)) {
      target = GEN_IPADD;
      addrlen = sizeof(struct in_addr);
    }

  /* get a "list" of alternative names */
  altnames = X509_get_ext_d2i(server_cert, NID_subject_alt_name, NULL, NULL);

  if(altnames) {
    int numalts;
    int i;

    /* get amount of alternatives, RFC2459 claims there MUST be at least
       one, but we don't depend on it... */
    numalts = sk_GENERAL_NAME_num(altnames);

    /* loop through all alternatives while none has matched */
    for (i=0; (i<numalts) && !matched; i++) {
      /* get a handle to alternative name number i */
      const GENERAL_NAME *check = sk_GENERAL_NAME_value(altnames, i);

      /* only check alternatives of the same type the target is */
      if(check->type == target) {
        /* get data and length */
        const char *altptr = (char *)ASN1_STRING_data(check->d.ia5);
        int altlen;

        switch(target) {
        case GEN_DNS: /* name/pattern comparison */
          /* The OpenSSL man page explicitly says: "In general it cannot be
             assumed that the data returned by ASN1_STRING_data() is null
             terminated or does not contain embedded nulls." But also that
             "The actual format of the data will depend on the actual string
             type itself: for example for and IA5String the data will be ASCII"

             Gisle researched the OpenSSL sources:
             "I checked the 0.9.6 and 0.9.8 sources before my patch and
             it always 0-terminates an IA5String."
          */
          if (cert_hostcheck(altptr, conn->host.name))
            matched = TRUE;
          break;

        case GEN_IPADD: /* IP address comparison */
          /* compare alternative IP address if the data chunk is the same size
             our server IP address is */
          altlen = ASN1_STRING_length(check->d.ia5);
          if((altlen == addrlen) && !memcmp(altptr, &addr, altlen))
            matched = TRUE;
          break;
        }
      }
    }
    GENERAL_NAMES_free(altnames);
  }

  if(matched)
    /* an alternative name matched the server hostname */
    infof(data, "\t subjectAltName: %s matched\n", conn->host.dispname);
  else {
    /* we have to look to the last occurence of a commonName in the
       distinguished one to get the most significant one. */
    int j,i=-1 ;

/* The following is done because of a bug in 0.9.6b */

    unsigned char *nulstr = (unsigned char *)"";
    unsigned char *peer_CN = nulstr;

    X509_NAME *name = X509_get_subject_name(server_cert) ;
    if (name)
      while ((j=X509_NAME_get_index_by_NID(name,NID_commonName,i))>=0)
        i=j;

    /* we have the name entry and we will now convert this to a string
       that we can use for comparison. Doing this we support BMPstring,
       UTF8 etc. */

    if (i>=0) {
      ASN1_STRING *tmp = X509_NAME_ENTRY_get_data(X509_NAME_get_entry(name,i));

      /* In OpenSSL 0.9.7d and earlier, ASN1_STRING_to_UTF8 fails if the input
         is already UTF-8 encoded. We check for this case and copy the raw
         string manually to avoid the problem. This code can be made
         conditional in the future when OpenSSL has been fixed. Work-around
         brought by Alexis S. L. Carvalho. */
      if (tmp && ASN1_STRING_type(tmp) == V_ASN1_UTF8STRING) {
        j = ASN1_STRING_length(tmp);
        if (j >= 0) {
          peer_CN = OPENSSL_malloc(j+1);
          if (peer_CN) {
            memcpy(peer_CN, ASN1_STRING_data(tmp), j);
            peer_CN[j] = '\0';
          }
        }
      }
      else /* not a UTF8 name */
        j = ASN1_STRING_to_UTF8(&peer_CN, tmp);
    }

    if (peer_CN == nulstr)
       peer_CN = NULL;

    if (!peer_CN) {
      if(data->set.ssl.verifyhost > 1) {
        failf(data,
              "SSL: unable to obtain common name from peer certificate");
        return CURLE_SSL_PEER_CERTIFICATE;
      }
      else {
        /* Consider verifyhost == 1 as an "OK" for a missing CN field, but we
           output a note about the situation */
        infof(data, "\t common name: WARNING couldn't obtain\n");
      }
    }
    else if(!cert_hostcheck((const char *)peer_CN, conn->host.name)) {
      if(data->set.ssl.verifyhost > 1) {
        failf(data, "SSL: certificate subject name '%s' does not match "
              "target host name '%s'", peer_CN, conn->host.dispname);
        res = CURLE_SSL_PEER_CERTIFICATE;
      }
      else
        infof(data, "\t common name: %s (does not match '%s')\n",
              peer_CN, conn->host.dispname);
    }
    else {
      infof(data, "\t common name: %s (matched)\n", peer_CN);
    }
    if(peer_CN)
      OPENSSL_free(peer_CN);
  }
  return res;
}
#endif