path: root/src/tls_remote.c

#include "tls_remote.h"

#include <unistd.h>

#include "byte.h"
#include "case.h"
#include "constmap.h"
#include "fmt.h"
#include "str.h"
#include "stralloc.h"

#include "dns.h"
#include "tls_errors.h"
#include "ucspissl.h"

/**
  @file  tls_remote.c -- TLS client functions
  @brief connection functions: tls_conn, tls_exit;
         verification functions: tls_certkey, tls_checkpeer, tls_fingerprint, tlsa_check;
         tls_destination, tls_domaincert
         dummy functions: tls_crlcheck

         tls_checkpeer:   r = 0 -> ADH, r = 1 -> wildcard DN, r = 2 -> DN, r = 3 -> CA; r < 0 -> error
         tls_fingerprint: r = 0 -> failed, r = 1 -> ok; r < 0 -> error
         tlsa_check:      r = 0 -> nothing, r = usage + 1, r < 0 -> error
*/

/* Caution: OpenSSL's X509_pubkey_digest() does not work as expected.
   I've included now: X509_pkey_digest() and X509_cert_digest() (as makro) */

#define X509_cert_digest X509_digest

int tls_certkey(SSL_CTX *ctx, const char *cert, const char *key, char *ppwd)
{
  if (!cert) return 0;

  if (SSL_CTX_use_certificate_chain_file(ctx, cert) != 1) return -1;

  if (!key) key = cert;

  if (ppwd) SSL_CTX_set_default_passwd_cb_userdata(ctx, ppwd);

  if (SSL_CTX_use_PrivateKey_file(ctx, key, SSL_FILETYPE_PEM) != 1) return -2;

  if (SSL_CTX_check_private_key(ctx) != 1) return -3;

  return 0;
}

int tls_conn(SSL *ssl, int smtpfd)
{
  SSL_set_options(ssl, SSL_OP_NO_SSLv2);
  SSL_set_options(ssl, SSL_OP_NO_SSLv3);
  return SSL_set_fd(ssl, smtpfd);
}

int tls_checkpeer(SSL *ssl, X509 *cert, const stralloc host, const int flag, const int verify)
{
  const GENERAL_NAME *ext;
  char buf[SSL_NAME_LEN];
  char *dnsname = 0;
  int dname = 0;
  int num;
  int len;
  int fflag;
  int i;
  int rc = 0;

  fflag = flag;
  if (flag > 20) fflag = flag - 20;
  if (flag > 10) fflag = flag - 10;

  /* X.509 CA DN/SAN name validation against DNS */

  if (host.len && fflag > 4) {
    GENERAL_NAMES *extensions = X509_get_ext_d2i(cert, NID_subject_alt_name, 0, 0);
    num = sk_GENERAL_NAME_num(extensions); /* num = 0, if no SAN extensions */

    for (i = 0; i < num; ++i) {
      ext = sk_GENERAL_NAME_value(extensions, i);
      if (ext->type == GEN_DNS) {
#if (OPENSSL_VERSION_NUMBER < 0x10100000L)  // 0xmnnffppsL
        if (ASN1_STRING_type(ext->d.ia5) != V_ASN1_IA5STRING) continue;
        dnsname = (char *)ASN1_STRING_data(ext->d.ia5);
#else
        if (OBJ_sn2nid((const char *)ext->d.ia5) != V_ASN1_IA5STRING) continue;
        dnsname = (char *)ASN1_STRING_get0_data(ext->d.ia5);
#endif
        len = ASN1_STRING_length(ext->d.ia5);
        dname = 1;
      }
    }

    if (!dname) {
      X509_NAME_get_text_by_NID(X509_get_subject_name(cert), NID_commonName, buf, sizeof(buf));
      buf[SSL_NAME_LEN - 1] = 0;
      dnsname = buf;
      len = SSL_NAME_LEN - 1;
    }

    switch (fflag) {
      case 5:
        if (dnsname[0] == '*' && dnsname[1] == '.')
          if (case_diffrs(dnsname + 1, host.s)) return -3;
        if (case_diffrs(dnsname, host.s)) return -3;
        rc = 3;
        break;
      case 6:
        if (case_diffs(dnsname, host.s)) return -3;
        rc = 2;
        break;
    }
  }

  /* X.509 CA Verification: root CA must be available */

  if (fflag > 3 && verify > -2) {
    if (SSL_get_verify_result(ssl) != X509_V_OK)
      return -2;
    else
      rc = 1;
  }

  return rc;
}

int tls_checkcrl(SSL *ssl)  // not implemented yet
{
  return 0;
}

int dig_ascii(char *digascii, const char *digest, const int len)
{
  static const char hextab[] = "0123456789abcdef";
  int j;

  for (j = 0; j < len; j++) {
    digascii[2 * j] = hextab[(unsigned char)digest[j] >> 4];
    digascii[2 * j + 1] = hextab[(unsigned char)digest[j] & 0x0f];
  }
  digascii[2 * len] = '\0';

  return (2 * j);  // 2*len
}

/*
  X509_pkey_digest() takes the same args as X509_digest();
  however returning the correct hash of pubkey in md.
  Subjects keys are restricted to 2048 byte in size.
  Return codes: 1: sucess, 0: failed.
*/
int X509_pkey_digest(const X509 *cert, const EVP_MD *type, unsigned char *md, unsigned int *dlen)
{
  unsigned int len = 0;
  unsigned int size = 2048;
  unsigned char *buf;
  unsigned char *buf2;
  unsigned char buffer[size];  // avoid malloc

  /*  Following Viktor's suggestion */

  if (!X509_get0_pubkey_bitstr(cert)) return 0;  // no Subject public key

  len = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), 0);
  if (len > size) return 0;
  buf2 = buf = buffer;
  i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), (unsigned char **)&buf2);
  if (buf2 - buf != len) return 0;

  if (!EVP_Digest(buf, len, md, dlen, type, 0)) return 0;  // OpenSSL voodoo
  return 1;
}

/*
  Return codes: -4: no X.509 cert (fatal), -3: matching error (deferred),
                -2: unsupported type, -1: weird TLSA record
                 0: No X.509 cert; seen: usage++;
*/
int tlsa_check(const STACK_OF(X509) * certs, const stralloc host, const unsigned long p)
{
  const EVP_MD *methodsha256 = EVP_sha256();
  const EVP_MD *methodsha512 = EVP_sha512();
  stralloc out = {0};
  stralloc sa = {0};
  stralloc cn = {0};
  unsigned char digest[EVP_MAX_MD_SIZE];
  unsigned int dlen = 0;
  unsigned int n = 0;
  int i = 0;
  int r;
  char port[FMT_ULONG];
  uint16 type;
  uint16 selector;
  uint16 usage;

  // construct TLSA FQDN -- simple procedure; returning Usage

  if (host.len < 2) return 0;
  if (!stralloc_copyb(&sa, "_", 1)) temp_nomem();
  port[fmt_ulong(port, p)] = 0;
  if (!stralloc_cats(&sa, port)) temp_nomem();
  if (!stralloc_cats(&sa, "._tcp.")) temp_nomem();
  if (!stralloc_cats(&sa, host.s)) temp_nomem();

  if (dns_cname(&cn, &sa) > 0) {  // query name could be a cname
    if (dns_tlsa(&out, &cn) <= 0) return 0;
  } else {
    if (dns_tlsa(&out, &sa) <= 0) return 0;
  }
  if (out.len < 5) return -1;

  /*  https://www.openssl.org/docs/man3.0/man3/X509_digest.html (1.1.1):
      "The len parameter, if not NULL, points to a place where the digest size will be stored."
      [sigh]
  */

  do {
    usage = (unsigned char)out.s[i];         // Usage: PKIX-TA [0], PKIX-EE [1], DANE-TA [2], DANE-EE [3]
    selector = (unsigned char)out.s[i + 1];  // Selector: 0 = Cert, 1 = SPKI
    type = (unsigned char)out.s[i + 2];      // Type: 0/1/2 = [Cert|SPKI]/SHA256/SHA512

    unsigned len = sk_X509_num(certs);
    for (n = 0; n < len; n++) {
      X509 *cert = sk_X509_value(certs, n);
      if (type == 1) {
        if (selector == 0) r = X509_cert_digest(cert, methodsha256, digest, &dlen);
        if (selector == 1) r = X509_pkey_digest(cert, methodsha256, digest, &dlen);
      } else if (type == 2) {
        if (selector == 0) r = X509_cert_digest(cert, methodsha512, digest, &dlen);
        if (selector == 1) r = X509_pkey_digest(cert, methodsha512, digest, &dlen);
      } else {
        return -2;
      }

      if (!byte_diff(digest, dlen, out.s + i + 3)) return ++usage;
    }

    i += (dlen + 3);
  } while (i < out.len - 4);

  return -3;
}

int tls_fingerprint(X509 *cert, const char *fingerprint, int dlen)
{
  const EVP_MD *methodsha1 = EVP_sha1();
  const EVP_MD *methodsha224 = EVP_sha224();
  const EVP_MD *methodsha256 = EVP_sha256();
  const EVP_MD *methodsha512 = EVP_sha512();
  unsigned char digest[EVP_MAX_MD_SIZE];
  unsigned char digascii[257];
  unsigned int len;

  switch (dlen) { /* fetch digest from cert; len = bitlength/8 */
    case 40:
      if (!X509_digest(cert, methodsha1, digest, &len)) return -2;
    case 56:
      if (!X509_digest(cert, methodsha224, digest, &len)) return -2;
    case 64:
      if (!X509_digest(cert, methodsha256, digest, &len)) return -2;
    case 128:
      if (!X509_digest(cert, methodsha512, digest, &len)) return -2;
    default: return -3;
  }

  len = dig_ascii(digascii, digest, len);
  if (!str_diffn(digascii, fingerprint, len)) return 1;

  return 0;
}

int tls_exit(SSL *ssl)
{
  if (SSL_shutdown(ssl) == 0) SSL_shutdown(ssl);
  return 0;
}

/**
  @brief tls_destination
  @param  stralloc hostname (maybe 0-terminated)

                               Certificate       Fallthru

  @return values: | ADH | Cert *DN FQDN Hash | noTLSA noTLS
        ----------+-----+--------------------+-------------
     optional TLS |  1  |  3    -    -    -  |   -     9
    mandatory TLS |  2  |  4    5    6    7  |   8

           no TLS   -1
*/
int tls_destination(const stralloc hostname)
{
  int i;
  stralloc tlshost = {0};
  stralloc tlsdest = {0};

  if (!stralloc_copy(&tlshost, &hostname)) temp_nomem();
  if (!stralloc_0(&tlshost)) temp_nomem();

  // Host rules

  if (!stralloc_copys(&tlsdest, "!")) temp_nomem();
  if (!stralloc_cats(&tlsdest, tlshost.s)) temp_nomem();
  if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return -1;

  if (!stralloc_copys(&tlsdest, "?")) temp_nomem();
  if (!stralloc_cats(&tlsdest, tlshost.s)) temp_nomem();
  if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 9;

  if (!stralloc_copys(&tlsdest, "/")) temp_nomem();
  if (!stralloc_cats(&tlsdest, tlshost.s)) temp_nomem();
  if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 8;

  if (!stralloc_copys(&tlsdest, "%")) temp_nomem();  // CERT + hash
  if (!stralloc_cats(&tlsdest, tlshost.s)) temp_nomem();
  if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 7;

  if (!stralloc_copys(&tlsdest, "=")) temp_nomem();  // CERT + FQDN
  if (!stralloc_cats(&tlsdest, tlshost.s)) temp_nomem();
  if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 6;

  if (!stralloc_copys(&tlsdest, "~")) temp_nomem();  // CERT + Wild
  if (!stralloc_cats(&tlsdest, tlshost.s)) temp_nomem();
  if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 5;

  // Domain rules

  for (i = 0; i < tlshost.len; ++i)  // TLS fallthru
    if ((i == 0) || (tlshost.s[i] == '.')) {
      if (!stralloc_copys(&tlsdest, "?")) temp_nomem();
      if (!stralloc_cats(&tlsdest, tlshost.s + i)) temp_nomem();
      if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 9;
    }

  for (i = 0; i < tlshost.len; ++i)  // no TLSA
    if ((i == 0) || (tlshost.s[i] == '.')) {
      if (!stralloc_copys(&tlsdest, "/")) temp_nomem();
      if (!stralloc_cats(&tlsdest, tlshost.s + i)) temp_nomem();
      if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 8;
    }

  for (i = 0; i < tlshost.len; ++i)  // CERT + Wild
    if ((i == 0) || (tlshost.s[i] == '.')) {
      if (!stralloc_copys(&tlsdest, "~")) temp_nomem();
      if (!stralloc_cats(&tlsdest, tlshost.s + i)) temp_nomem();
      if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 5;
    }

  for (i = 0; i < tlshost.len; ++i)  // CERT - generic
    if ((i == 0) || (tlshost.s[i] == '.')) {
      if (!stralloc_copys(&tlsdest, "")) temp_nomem();
      if (!stralloc_cats(&tlsdest, tlshost.s + i)) temp_nomem();
      if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 4;
    }

  for (i = 0; i < tlshost.len; ++i)  // ADH per host/domain
    if ((i == 0) || (tlshost.s[i] == '.')) {
      if (!stralloc_copys(&tlsdest, "-")) temp_nomem();
      if (!stralloc_cats(&tlsdest, tlshost.s + i)) temp_nomem();
      if ((tlsdestinfo = constmap(&maptlsdestinations, tlsdest.s, tlsdest.len))) return 2;
    }

  // General rules (mandatory TLS)

  tlsdestinfo = 0;
  if (constmap(&maptlsdestinations, "/*", 2)) return 8;  // no TLSA
  if (constmap(&maptlsdestinations, "=*", 2)) return 6;  // CERT + FQDN
  if (constmap(&maptlsdestinations, "~*", 2)) return 5;  // CERT + Wild
  if (constmap(&maptlsdestinations, "+*", 2)) return 4;  // CERT
  if (constmap(&maptlsdestinations, "-*", 2)) return 2;  // ADH

  // Fall thru rules (optional TLS)

  if (constmap(&maptlsdestinations, "?", 1)) return 9;  // fallback to no TLS
  if (constmap(&maptlsdestinations, "*", 1)) return 3;  // CERT
  if (constmap(&maptlsdestinations, "-", 1)) return 1;  // ADH

  return 0;
}

int tls_domaincerts(const stralloc domainname)
{
  int i;
  tlsdomaininfo = 0;  // extern

  /* Our Certs - per domain */

  if (domainname.len)
    for (i = 0; i < domainname.len; ++i)
      if ((i == 0) || (domainname.s[i] == '.'))
        if ((tlsdomaininfo = constmap(&mapdomaincerts, domainname.s + i, domainname.len - i))) return 2;

  /* Standard Cert (if any) */

  if ((tlsdomaininfo = constmap(&mapdomaincerts, "*", 1))) return 1;

  return 0;
}