Socat patch to add hash verification to openSSL connections

socat-add-verify-hash.patch

commit 49d13df85993eda521002b9c197d68914c0c86e6
Author: gdm85 <gdm85@users.noreply.github.com>
Date:   Tue Nov 14 23:21:23 2017 +0100

    [PATCH] Add support for openssl-verify-hash
    
    A new option is added, openssl-verify-hash with alias verify-hash; this option
    specifies a SHA256 hash in hexadecimal format that will be required to match
    the X509 hash of the OpenSSL peer certificate.
    Documentation is updated to mention MiTM for the pre-existing 'verify' option
    and clarify the role of the new 'verify-hash' option for self-signed
    certificates (not mentioned explicitly) and certificate pinning.

diff --git a/doc/socat.yo b/doc/socat.yo
index 258686e..7bad574 100644
--- a/doc/socat.yo
+++ b/doc/socat.yo
@@ -508,6 +508,7 @@ label(ADDRESS_OPENSSL_CONNECT)dit(bf(tt(OPENSSL:<host>:<port>)))
    link(cipher)(OPTION_OPENSSL_CIPHERLIST),
    link(method)(OPTION_OPENSSL_METHOD),
    link(verify)(OPTION_OPENSSL_VERIFY),
+   link(verify-hash)(OPTION_OPENSSL_VERIFY_HASH),
    link(commonname)(OPTION_OPENSSL_COMMONNAME)
    link(cafile)(OPTION_OPENSSL_CAFILE),
    link(capath)(OPTION_OPENSSL_CAPATH),
@@ -2646,8 +2647,12 @@ label(OPTION_OPENSSL_METHOD)dit(bf(tt(method=<ssl-method>)))
    dit(tt(DTLS1)) Select DTLS protocol version 1.
    enddit()
 label(OPTION_OPENSSL_VERIFY)dit(bf(tt(verify=<bool>)))
-   Controls check of the peer's certificate. Default is 1 (true). Disabling
-   verify might open your socket for everyone, making the encryption useless!
+   Controls verification of the peer's certificate. Default is 1 (true). Disabling
+   verify makes you vulnerable to man-in-the-middle attacks!
+label(OPTION_OPENSSL_VERIFY_HASH)dit(bf(tt(verify-hash=<string>)))
+   Requires the OpenSSL peer certificate SHA256 hash to match specified string
+   (case-insensitive). This mitigates disabled link(OpenSSL certificate verification)(OPTION_OPENSSL_VERIFY) or
+   works as certificate pinning together with verification.
 label(OPTION_OPENSSL_CERTIFICATE)dit(bf(tt(cert=<filename>)))
    Specifies the file with the certificate and private key for authentication. 
    The certificate must be in OpenSSL format (*.pem). 
diff --git a/doc/xio.help b/doc/xio.help
index 2053419..28f7539 100644
--- a/doc/xio.help
+++ b/doc/xio.help
@@ -397,7 +397,7 @@ Note: this is currently only an experimental integration of openssl!
 (it does not provide any trust between the peers because is does not check
 certificates!)
 Option groups: FD,SOCKET,SOCK_IP4,IP_TCP,OPENSSL,RETRY
-Useful options: cipher, method, verify, cafile, capath, certificate, bind, sourceport, retry
+Useful options: cipher, method, verify, verify-hash, cafile, capath, certificate, bind, sourceport, retry
 
 
 OPENSSL-LISTEN:port
@@ -4514,6 +4514,19 @@ Platforms: (depends on openssl installation)
    verify might open your socket for everyone! 
 
 
+Option: openssl-verify-hash=string
+Aliases: verify-hash=string
+
+Type: STRING_NULL
+Option group: OPENSSL
+Phase: SPEC
+Platforms: (depends on openssl installation)
+
+Requires the OpenSSL peer certificate SHA256 hash to match specified string
+(case-insensitive). This mitigates disabled OpenSSL certificate verification or
+works as certificate pinning together with verification.
+
+
 Option: openssl-certificate=file
 Aliases: cert=file
 
diff --git a/xio-openssl.c b/xio-openssl.c
index e931983..135ec55 100644
--- a/xio-openssl.c
+++ b/xio-openssl.c
@@ -51,9 +51,10 @@ static int openssl_SSL_ERROR_SSL(int level, const char *funcname);
 static int openssl_handle_peer_certificate(struct single *xfd,
 					   const char *peername,
 					   bool opt_ver,
+					   const char *opt_ver_hash,
 					   int level);
 static int xioSSL_set_fd(struct single *xfd, int level);
-static int xioSSL_connect(struct single *xfd, const char *opt_commonname, bool opt_ver, int level);
+static int xioSSL_connect(struct single *xfd, const char *opt_commonname, bool opt_ver, const char *opt_ver_hash, int level);
 static int openssl_delete_cert_info(void);
 
 
@@ -103,6 +104,7 @@ const struct addrdesc addr_openssl_listen = {
 const struct optdesc opt_openssl_cipherlist = { "openssl-cipherlist", "ciphers", OPT_OPENSSL_CIPHERLIST, GROUP_OPENSSL, PH_SPEC, TYPE_STRING, OFUNC_SPEC };
 const struct optdesc opt_openssl_method     = { "openssl-method",     "method",  OPT_OPENSSL_METHOD,     GROUP_OPENSSL, PH_SPEC, TYPE_STRING, OFUNC_SPEC };
 const struct optdesc opt_openssl_verify     = { "openssl-verify",     "verify",  OPT_OPENSSL_VERIFY,     GROUP_OPENSSL, PH_SPEC, TYPE_BOOL,   OFUNC_SPEC };
+const struct optdesc opt_openssl_verify_hash = { "openssl-verify-hash", "verify-hash", OPT_OPENSSL_VERIFY_HASH, GROUP_OPENSSL, PH_SPEC, TYPE_STRING_NULL, OFUNC_SPEC };
 const struct optdesc opt_openssl_certificate = { "openssl-certificate", "cert",  OPT_OPENSSL_CERTIFICATE, GROUP_OPENSSL, PH_SPEC, TYPE_FILENAME, OFUNC_SPEC };
 const struct optdesc opt_openssl_key         = { "openssl-key",         "key",   OPT_OPENSSL_KEY,         GROUP_OPENSSL, PH_SPEC, TYPE_FILENAME, OFUNC_SPEC };
 const struct optdesc opt_openssl_dhparam     = { "openssl-dhparam",     "dh",    OPT_OPENSSL_DHPARAM,     GROUP_OPENSSL, PH_SPEC, TYPE_FILENAME, OFUNC_SPEC };
@@ -195,6 +197,7 @@ static int
    int level;
    SSL_CTX* ctx;
    bool opt_ver = true;	/* verify peer certificate */
+   char *opt_ver_hash = NULL;
    char *opt_cert = NULL;	/* file name of client certificate */
    const char *opt_commonname = NULL;	/* for checking peer certificate */
    int result;
@@ -232,7 +235,7 @@ static int
    }
 
    result =
-      _xioopen_openssl_prepare(opts, xfd, false, &opt_ver, opt_cert, &ctx);
+      _xioopen_openssl_prepare(opts, xfd, false, &opt_ver, &opt_ver_hash, opt_cert, &ctx);
    if (result != STAT_OK)  return STAT_NORETRY;
 
    result =
@@ -289,7 +292,7 @@ static int
 	 return result;
       }
 
-      result = _xioopen_openssl_connect(xfd, opt_ver, opt_commonname, ctx, level);
+      result = _xioopen_openssl_connect(xfd, opt_ver, opt_ver_hash, opt_commonname, ctx, level);
       switch (result) {
       case STAT_OK: break;
 #if WITH_RETRY
@@ -357,6 +360,7 @@ static int
    SSL connection from an FD and a CTX. */
 int _xioopen_openssl_connect(struct single *xfd,
 			     bool opt_ver,
+                             const char *opt_ver_hash,
 			     const char *opt_commonname,
 			     SSL_CTX *ctx,
 			     int level) {
@@ -382,7 +386,7 @@ int _xioopen_openssl_connect(struct single *xfd,
       return result;
    }
 
-   result = xioSSL_connect(xfd, opt_commonname, opt_ver, level);
+   result = xioSSL_connect(xfd, opt_commonname, opt_ver, opt_ver_hash, level);
    if (result != STAT_OK) {
       sycSSL_free(xfd->para.openssl.ssl);
       xfd->para.openssl.ssl = NULL;
@@ -390,7 +394,7 @@ int _xioopen_openssl_connect(struct single *xfd,
    }
 
    result = openssl_handle_peer_certificate(xfd, opt_commonname,
-					    opt_ver, level);
+					    opt_ver, opt_ver_hash, level);
    if (result != STAT_OK) {
       sycSSL_free(xfd->para.openssl.ssl);
       xfd->para.openssl.ssl = NULL;
@@ -431,6 +435,7 @@ static int
    int level;
    SSL_CTX* ctx;
    bool opt_ver = true;	/* verify peer certificate - changed with 1.6.0 */
+   char *unused_opt_ver_hash = NULL;
    char *opt_cert = NULL;	/* file name of server certificate */
    const char *opt_commonname = NULL;	/* for checking peer certificate */
    int result;
@@ -470,7 +475,7 @@ static int
    applyopts(-1, opts, PH_EARLY);
 
    result =
-      _xioopen_openssl_prepare(opts, xfd, true, &opt_ver, opt_cert, &ctx);
+      _xioopen_openssl_prepare(opts, xfd, true, &opt_ver, &unused_opt_ver_hash, opt_cert, &ctx);
    if (result != STAT_OK)  return STAT_NORETRY;
 
    if (_xioopen_ipapp_listen_prepare(opts, &opts0, portname, &pf, ipproto,
@@ -641,7 +646,7 @@ int _xioopen_openssl_listen(struct single *xfd,
       return STAT_RETRYLATER;
    }
 
-   if (openssl_handle_peer_certificate(xfd, opt_commonname, opt_ver, E_ERROR/*!*/) < 0) {
+   if (openssl_handle_peer_certificate(xfd, opt_commonname, opt_ver, NULL, E_ERROR/*!*/) < 0) {
       return STAT_NORETRY;
    }
 
@@ -711,6 +716,7 @@ int
 					       */
 			    bool server,	/* SSL client: false */
 			    bool *opt_ver,
+			    char **opt_ver_hash,
 			    const char *opt_cert,
 			    SSL_CTX **ctx)
 {
@@ -737,6 +743,7 @@ int
    retropt_string(opts, OPT_OPENSSL_METHOD, &me_str);
    retropt_string(opts, OPT_OPENSSL_CIPHERLIST, &ci_str);
    retropt_bool(opts, OPT_OPENSSL_VERIFY, opt_ver);
+   retropt_string(opts, OPT_OPENSSL_VERIFY_HASH, opt_ver_hash);
    retropt_string(opts, OPT_OPENSSL_CAFILE, &opt_cafile);
    retropt_string(opts, OPT_OPENSSL_CAPATH, &opt_capath);
    retropt_string(opts, OPT_OPENSSL_KEY, &opt_key);
@@ -1357,6 +1364,37 @@ static bool openssl_check_peername(X509_NAME *name, const char *peername) {
    return openssl_check_name((const char *)text, peername);
 }
 
+static bool xioSSL_verify_cert_sha256(X509* cert, const char *expected_fp) {
+   uint8_t hash[EVP_MAX_MD_SIZE];
+   char cert_fp[256/8*3];
+   uint32_t len = sizeof(hash);
+   uint32_t buflen = sizeof(cert_fp);
+   int i, ok;
+   int pos = 0;
+
+   /* calculate certificate SHA256 hash */
+   ok = X509_digest(cert, EVP_sha256(), hash, &len);
+   if (ok != 1) {
+     Error("failed to calculate certificate hash");
+     return false;
+   }
+
+   for(i = 0; i < len; ++i) {
+     if (i > 0) {
+       pos += snprintf(cert_fp + pos, buflen - pos, ":");
+     }
+     pos += snprintf(cert_fp + pos, buflen - pos, "%02X", hash[i]);
+   }
+   cert_fp[pos] = 0;
+
+   if (!strcasecmp(expected_fp, cert_fp)) {
+      return true;
+   }
+
+   Error2("certificate hash \"%s\" does not match expected \"%s\"", cert_fp, expected_fp);
+   return false;
+}
+
 /* retrieves certificate provided by peer, sets env vars containing
    certificates field values, and checks peername if provided by
    calling function */
@@ -1366,7 +1404,7 @@ static bool openssl_check_peername(X509_NAME *name, const char *peername) {
 */
 static int openssl_handle_peer_certificate(struct single *xfd,
 					   const char *peername,
-					   bool opt_ver, int level) {
+					   bool opt_ver, const char *opt_ver_hash, int level) {
    X509 *peer_cert;
    X509_NAME *subjectname, *issuername;
    /*ASN1_TIME not_before, not_after;*/
@@ -1460,12 +1498,19 @@ pName->d.ia5);
 		  }
 	       }
 	    }
-	 }
+         }
+      }
+   }
+
+   if (opt_ver_hash) {
+      if (false == xioSSL_verify_cert_sha256(peer_cert, opt_ver_hash)) {
+	X509_free(peer_cert);
+        return STAT_NORETRY;
       }
    }
 
    if (!opt_ver) {
-      Notice("option openssl-verify disabled, no check of certificate");
+      Notice("option openssl-verify disabled, no further checks of certificate");
       X509_free(peer_cert);
       return STAT_OK;
    }
@@ -1513,7 +1558,7 @@ static int xioSSL_set_fd(struct single *xfd, int level) {
    options and ev. sleeps an interval. It returns NORETRY when the caller
    should not retry for any reason. */
 static int xioSSL_connect(struct single *xfd, const char *opt_commonname,
-			  bool opt_ver, int level) {
+			  bool opt_ver, const char *opt_ver_hash, int level) {
    char error_string[120];
    int errint, status, ret;
    unsigned long err;
@@ -1558,7 +1603,7 @@ static int xioSSL_connect(struct single *xfd, const char *opt_commonname,
 	 break;
       case SSL_ERROR_SSL:
 	 status = openssl_SSL_ERROR_SSL(level, "SSL_connect");
-	 if (openssl_handle_peer_certificate(xfd, opt_commonname, opt_ver, level/*!*/) < 0) {
+	 if (openssl_handle_peer_certificate(xfd, opt_commonname, opt_ver, opt_ver_hash, level/*!*/) < 0) {
 	    return STAT_RETRYLATER;
 	 }
 	 break;
diff --git a/xio-openssl.h b/xio-openssl.h
index ca47233..9f425b1 100644
--- a/xio-openssl.h
+++ b/xio-openssl.h
@@ -16,6 +16,7 @@ extern const struct addrdesc addr_openssl_listen;
 extern const struct optdesc opt_openssl_cipherlist;
 extern const struct optdesc opt_openssl_method;
 extern const struct optdesc opt_openssl_verify;
+extern const struct optdesc opt_openssl_verify_hash;
 extern const struct optdesc opt_openssl_certificate;
 extern const struct optdesc opt_openssl_key;
 extern const struct optdesc opt_openssl_dhparam;
@@ -33,10 +34,10 @@ extern const struct optdesc opt_openssl_commonname;
 
 extern int
    _xioopen_openssl_prepare(struct opt *opts, struct single *xfd,
-			    bool server, bool *opt_ver, const char *opt_cert,
+			    bool server, bool *opt_ver, char **opt_ver_hash, const char *opt_cert,
 			    SSL_CTX **ctx);
 extern int
-   _xioopen_openssl_connect(struct single *xfd,  bool opt_ver,
+   _xioopen_openssl_connect(struct single *xfd,  bool opt_ver, const char *opt_ver_hash,
 			    const char *opt_commonname,
 			    SSL_CTX *ctx, int level);
 extern int
diff --git a/xioopts.c b/xioopts.c
index 9ea6ce4..ba418da 100644
--- a/xioopts.c
+++ b/xioopts.c
@@ -1112,6 +1112,7 @@ const struct optname optionnames[] = {
 	IF_OPENSSL("openssl-method",	&opt_openssl_method)
 	IF_OPENSSL("openssl-pseudo",	&opt_openssl_pseudo)
 	IF_OPENSSL("openssl-verify",	&opt_openssl_verify)
+	IF_OPENSSL("openssl-verify-hash", &opt_openssl_verify_hash)
 	IF_TERMIOS("opost",	&opt_opost)
 #if defined(HAVE_TERMIOS_ISPEED) && defined(OSPEED_OFFSET) && (OSPEED_OFFSET != -1)
 	IF_TERMIOS("ospeed",	&opt_ospeed)
@@ -1687,6 +1688,7 @@ const struct optname optionnames[] = {
 	IF_TERMIOS("veol2",	&opt_veol2)
 	IF_TERMIOS("verase",	&opt_verase)
 	IF_OPENSSL("verify",	&opt_openssl_verify)
+	IF_OPENSSL("verify-hash", &opt_openssl_verify_hash)
 	IF_TERMIOS("vintr",	&opt_vintr)
 	IF_TERMIOS("vkill",	&opt_vkill)
 	IF_TERMIOS("vlnext",	&opt_vlnext)
diff --git a/xioopts.h b/xioopts.h
index 95a44a4..1b5fa76 100644
--- a/xioopts.h
+++ b/xioopts.h
@@ -484,6 +484,7 @@ enum e_optcode {
    OPT_OPENSSL_METHOD,
    OPT_OPENSSL_PSEUDO,
    OPT_OPENSSL_VERIFY,
+   OPT_OPENSSL_VERIFY_HASH,
    OPT_OPOST,		/* termios.c_oflag */
    OPT_OSPEED,		/* termios.c_ospeed */
    OPT_O_APPEND,