Bug#17208 SSL: client does not verify server certificate

 - Add new function 'ssl_verify_server_cert' which is used if we are 
   connecting to the server with SSL. It will compare the hostname in 
   the server's cert against the hostname that we used when connecting 
   to the server. Will reject the connection if hostname does not match.
 - Add new option "OPT_SSL_VERIFY_SERVER_CERT" to be passed to mysql_options
   which will turn on checking of servers cert.
 - Add new argument "ssl-verify-server-cert" to all mysql* clients which 
   will activate the above option.
 - Generate a new server cert with 1024 bits that has "localhost" as the server name.

SSL/server-cert.pem

 Certificate:
     Data:
         Version: 3 (0x2)
-        Serial Number: 2 (0x2)
+        Serial Number:
+            e9:07:d1:01:94:ee:66:ca
         Signature Algorithm: md5WithRSAEncryption
-        Issuer: C=SE, L=Uppsala, O=MySQL AB, CN=Abstract MySQL Developer/Email=abstract.mysql.developer@mysql.com
+        Issuer: C=SE, ST=Uppsala, L=Uppsala, O=MySQL AB, CN=localhost/emailAddress=abstract.mysql.developer@mysql.com
         Validity
-            Not Before: Sep 12 16:22:06 2003 GMT
-            Not After : Sep  9 16:22:06 2013 GMT
-        Subject: C=SE, L=Uppsala, O=MySQL AB, CN=MySQL Server/Email=abstract.mysql.developer@mysql.com
+            Not Before: Apr 18 15:35:37 2006 GMT
+            Not After : Jan 12 15:35:37 2009 GMT
+        Subject: C=SE, ST=Uppsala, L=Uppsala, O=MySQL AB, CN=localhost/emailAddress=abstract.mysql.developer@mysql.com
         Subject Public Key Info:
             Public Key Algorithm: rsaEncryption
             RSA Public Key: (1024 bit)
@@ -23,45 +24,42 @@ Certificate:
                     3d:0e:4d:2a:a8:b8:ca:99:8d
                 Exponent: 65537 (0x10001)
         X509v3 extensions:
-            X509v3 Basic Constraints: 
-                CA:FALSE
-            Netscape Comment: 
-                OpenSSL Generated Certificate
             X509v3 Subject Key Identifier: 
                 6E:E4:9B:6A:C5:EA:E4:E6:C7:EF:D7:1E:C8:63:45:60:2B:1B:D4:D4
             X509v3 Authority Key Identifier: 
-                keyid:88:98:65:D9:F3:F2:8B:03:1D:66:60:61:23:FA:AD:73:6D:D3:68:92
-                DirName:/C=SE/L=Uppsala/O=MySQL AB/CN=Abstract MySQL Developer/Email=abstract.mysql.developer@mysql.com
-                serial:00
+                keyid:6E:E4:9B:6A:C5:EA:E4:E6:C7:EF:D7:1E:C8:63:45:60:2B:1B:D4:D4
+                DirName:/C=SE/ST=Uppsala/L=Uppsala/O=MySQL AB/CN=localhost/emailAddress=abstract.mysql.developer@mysql.com
+                serial:E9:07:D1:01:94:EE:66:CA
 
+            X509v3 Basic Constraints: 
+                CA:TRUE
     Signature Algorithm: md5WithRSAEncryption
-        31:77:69:b9:bd:ab:29:f3:fc:5a:09:16:6f:5d:42:ea:ba:01:
-        55:69:e3:75:cf:b8:d1:b7:b9:bf:da:63:85:8c:48:92:06:60:
-        76:97:e0:00:78:4b:ad:da:ab:6a:90:6d:8b:03:a8:b1:e9:09:
-        78:e1:29:98:56:12:60:6b:42:fe:e8:a7:c4:f8:d6:15:07:e8:
-        2b:c2:d8:8a:e5:1b:2e:51:08:9b:56:e3:b3:7a:4c:3e:e5:be:
-        4a:4d:f8:65:7b:a8:21:e0:ca:fe:8b:ab:d7:ec:f2:2d:f7:d0:
-        bf:d7:c5:23:1c:08:d8:aa:57:c7:f3:5f:ba:33:3f:78:d1:f4:
-        8e:5e
+        1f:03:59:6e:ff:1f:9d:c7:19:9e:8e:b2:1a:c0:0b:9e:ee:94:
+        35:77:2a:93:04:ea:d5:a8:fc:36:5a:5b:e3:1c:02:b8:cf:04:
+        6e:21:b0:27:f6:96:6e:d6:8f:cd:02:cf:23:f3:e7:ff:6a:ee:
+        a9:09:c5:c9:07:81:b6:d2:bc:bd:13:47:0d:7b:76:f6:8a:c4:
+        76:24:f8:4c:4e:26:fc:d8:c0:1f:3d:40:19:43:8e:41:ab:99:
+        3a:99:9b:24:7c:ae:78:f3:df:2f:a2:ed:8f:27:0a:0a:0b:04:
+        bf:25:74:88:87:96:c8:68:d5:bc:5b:a0:ef:14:aa:53:6e:c4:
+        a3:e3
 -----BEGIN CERTIFICATE-----
-MIIDkTCCAvqgAwIBAgIBAjANBgkqhkiG9w0BAQQFADCBiDELMAkGA1UEBhMCU0Ux
-EDAOBgNVBAcTB1VwcHNhbGExETAPBgNVBAoTCE15U1FMIEFCMSEwHwYDVQQDExhB
-YnN0cmFjdCBNeVNRTCBEZXZlbG9wZXIxMTAvBgkqhkiG9w0BCQEWImFic3RyYWN0
-Lm15c3FsLmRldmVsb3BlckBteXNxbC5jb20wHhcNMDMwOTEyMTYyMjA2WhcNMTMw
-OTA5MTYyMjA2WjB8MQswCQYDVQQGEwJTRTEQMA4GA1UEBxMHVXBwc2FsYTERMA8G
-A1UEChMITXlTUUwgQUIxFTATBgNVBAMTDE15U1FMIFNlcnZlcjExMC8GCSqGSIb3
-DQEJARYiYWJzdHJhY3QubXlzcWwuZGV2ZWxvcGVyQG15c3FsLmNvbTCBnzANBgkq
-hkiG9w0BAQEFAAOBjQAwgYkCgYEA6YZ6VYSITL6k+JJzMBJJC3qFhzk0OQ19C40Y
-wheVE1LSP1UQV8g/WvWy+ovQZ0nMqoL8n84AtHPzNtI608KwDhTD1LIhdKHwMYFg
-h5hzXBDBsRpN8fOwmD/w15ebK/3VIXmyL+tkFcmbnfyeLdT4BFvqqXVLQsM9Dk0q
-qLjKmY0CAwEAAaOCARQwggEQMAkGA1UdEwQCMAAwLAYJYIZIAYb4QgENBB8WHU9w
-ZW5TU0wgR2VuZXJhdGVkIENlcnRpZmljYXRlMB0GA1UdDgQWBBRu5Jtqxerk5sfv
-1x7IY0VgKxvU1DCBtQYDVR0jBIGtMIGqgBSImGXZ8/KLAx1mYGEj+q1zbdNokqGB
-jqSBizCBiDELMAkGA1UEBhMCU0UxEDAOBgNVBAcTB1VwcHNhbGExETAPBgNVBAoT
-CE15U1FMIEFCMSEwHwYDVQQDExhBYnN0cmFjdCBNeVNRTCBEZXZlbG9wZXIxMTAv
-BgkqhkiG9w0BCQEWImFic3RyYWN0Lm15c3FsLmRldmVsb3BlckBteXNxbC5jb22C
-AQAwDQYJKoZIhvcNAQEEBQADgYEAMXdpub2rKfP8WgkWb11C6roBVWnjdc+40be5
-v9pjhYxIkgZgdpfgAHhLrdqrapBtiwOosekJeOEpmFYSYGtC/uinxPjWFQfoK8LY
-iuUbLlEIm1bjs3pMPuW+Sk34ZXuoIeDK/our1+zyLffQv9fFIxwI2KpXx/NfujM/
-eNH0jl4=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==
 -----END CERTIFICATE-----

client/client_priv.h

@@ -51,5 +51,5 @@ enum options_client
 #endif
   OPT_TRIGGERS,
   OPT_IGNORE_TABLE,OPT_INSERT_IGNORE,OPT_SHOW_WARNINGS,OPT_DROP_DATABASE,
-  OPT_TZ_UTC, OPT_AUTO_CLOSE
+  OPT_TZ_UTC, OPT_AUTO_CLOSE, OPT_SSL_VERIFY_SERVER_CERT
 };

client/mysql.cc

@@ -3123,6 +3123,8 @@ sql_real_connect(char *host,char *database,char *user,char *password,
   if (opt_use_ssl)
     mysql_ssl_set(&mysql, opt_ssl_key, opt_ssl_cert, opt_ssl_ca,
 		  opt_ssl_capath, opt_ssl_cipher);
+  mysql_options(&mysql,MYSQL_OPT_SSL_VERIFY_SERVER_CERT,
+                (char*)&opt_ssl_verify_server_cert);
 #endif
   if (opt_protocol)
     mysql_options(&mysql,MYSQL_OPT_PROTOCOL,(char*)&opt_protocol);

client/mysqladmin.cc

@@ -340,6 +340,8 @@ int main(int argc,char *argv[])
   if (opt_use_ssl)
     mysql_ssl_set(&mysql, opt_ssl_key, opt_ssl_cert, opt_ssl_ca,
 		  opt_ssl_capath, opt_ssl_cipher);
+  mysql_options(&mysql,MYSQL_OPT_SSL_VERIFY_SERVER_CERT,
+                (char*)&opt_ssl_verify_server_cert);
 #endif
   if (opt_protocol)
     mysql_options(&mysql,MYSQL_OPT_PROTOCOL,(char*)&opt_protocol);

client/mysqldump.c

@@ -905,6 +905,8 @@ static int dbConnect(char *host, char *user,char *passwd)
   if (opt_use_ssl)
     mysql_ssl_set(&mysql_connection, opt_ssl_key, opt_ssl_cert, opt_ssl_ca,
 		  opt_ssl_capath, opt_ssl_cipher);
+  mysql_options(&mysql_connection,MYSQL_OPT_SSL_VERIFY_SERVER_CERT,
+                (char*)&opt_ssl_verify_server_cert);
 #endif
   if (opt_protocol)
     mysql_options(&mysql_connection,MYSQL_OPT_PROTOCOL,(char*)&opt_protocol);

client/mysqlimport.c

@@ -384,6 +384,8 @@ static MYSQL *db_connect(char *host, char *database, char *user, char *passwd)
   if (opt_use_ssl)
     mysql_ssl_set(&mysql_connection, opt_ssl_key, opt_ssl_cert, opt_ssl_ca,
 		  opt_ssl_capath, opt_ssl_cipher);
+  mysql_options(&mysql_connection,MYSQL_OPT_SSL_VERIFY_SERVER_CERT,
+                (char*)&opt_ssl_verify_server_cert);
 #endif
   if (opt_protocol)
     mysql_options(&mysql_connection,MYSQL_OPT_PROTOCOL,(char*)&opt_protocol);

client/mysqlshow.c

@@ -109,6 +109,8 @@ int main(int argc, char **argv)
   if (opt_use_ssl)
     mysql_ssl_set(&mysql, opt_ssl_key, opt_ssl_cert, opt_ssl_ca,
 		  opt_ssl_capath, opt_ssl_cipher);
+  mysql_options(&mysql,MYSQL_OPT_SSL_VERIFY_SERVER_CERT,
+                (char*)&opt_ssl_verify_server_cert);
 #endif
   if (opt_protocol)
     mysql_options(&mysql,MYSQL_OPT_PROTOCOL,(char*)&opt_protocol);

client/mysqltest.c

@@ -108,7 +108,7 @@ enum {OPT_MANAGER_USER=256,OPT_MANAGER_HOST,OPT_MANAGER_PASSWD,
       OPT_MANAGER_PORT,OPT_MANAGER_WAIT_TIMEOUT, OPT_SKIP_SAFEMALLOC,
       OPT_SSL_SSL, OPT_SSL_KEY, OPT_SSL_CERT, OPT_SSL_CA, OPT_SSL_CAPATH,
       OPT_SSL_CIPHER,OPT_PS_PROTOCOL,OPT_SP_PROTOCOL,OPT_CURSOR_PROTOCOL,
-      OPT_VIEW_PROTOCOL};
+      OPT_VIEW_PROTOCOL, OPT_SSL_VERIFY_SERVER_CERT};
 
 /* ************************************************************************ */
 /*
@@ -2378,8 +2378,12 @@ int do_connect(struct st_query *q)
 
 #ifdef HAVE_OPENSSL
   if (opt_use_ssl || con_ssl)
+  {
     mysql_ssl_set(&next_con->mysql, opt_ssl_key, opt_ssl_cert, opt_ssl_ca,
 		  opt_ssl_capath, opt_ssl_cipher);
+    mysql_options(&next_con->mysql, MYSQL_OPT_SSL_VERIFY_SERVER_CERT,
+                  &opt_ssl_verify_server_cert);
+  }
 #endif
   if (con_sock && !free_con_sock && *con_sock && *con_sock != FN_LIBCHAR)
     con_sock=fn_format(buff, con_sock, TMPDIR, "",0);
@@ -4604,9 +4608,14 @@ int main(int argc, char **argv)
   mysql_options(&cur_con->mysql, MYSQL_SET_CHARSET_NAME, charset_name);
 
 #ifdef HAVE_OPENSSL
+  opt_ssl_verify_server_cert= TRUE; /* Always on in mysqltest */
   if (opt_use_ssl)
+  {
     mysql_ssl_set(&cur_con->mysql, opt_ssl_key, opt_ssl_cert, opt_ssl_ca,
 		  opt_ssl_capath, opt_ssl_cipher);
+    mysql_options(&cur_con->mysql, MYSQL_OPT_SSL_VERIFY_SERVER_CERT,
+                  &opt_ssl_verify_server_cert);
+  }
 #endif
 
   if (!(cur_con->name = my_strdup("default", MYF(MY_WME))))

include/mysql.h

@@ -149,7 +149,8 @@ enum mysql_option
   MYSQL_OPT_WRITE_TIMEOUT, MYSQL_OPT_USE_RESULT,
   MYSQL_OPT_USE_REMOTE_CONNECTION, MYSQL_OPT_USE_EMBEDDED_CONNECTION,
   MYSQL_OPT_GUESS_CONNECTION, MYSQL_SET_CLIENT_IP, MYSQL_SECURE_AUTH,
-  MYSQL_REPORT_DATA_TRUNCATION, MYSQL_OPT_RECONNECT
+  MYSQL_REPORT_DATA_TRUNCATION, MYSQL_OPT_RECONNECT,
+  MYSQL_OPT_SSL_VERIFY_SERVER_CERT
 };
 
 struct st_mysql_options {
@@ -164,6 +165,7 @@ struct st_mysql_options {
   char *ssl_ca;					/* PEM CA file */
   char *ssl_capath;				/* PEM directory of CA-s? */
   char *ssl_cipher;				/* cipher to use */
+  my_bool ssl_verify_server_cert;		/* if to verify server cert */
   char *shared_memory_base_name;
   unsigned long max_allowed_packet;
   my_bool use_ssl;				/* if to use SSL or not */

include/sslopt-longopts.h

@@ -37,5 +37,10 @@
   {"ssl-cipher", OPT_SSL_CIPHER, "SSL cipher to use (implies --ssl).",
    (gptr*) &opt_ssl_cipher, (gptr*) &opt_ssl_cipher, 0, GET_STR, REQUIRED_ARG,
    0, 0, 0, 0, 0, 0},
-
+#ifdef MYSQL_CLIENT
+  {"ssl-verify-server-cert", OPT_SSL_VERIFY_SERVER_CERT,
+   "Verify servers \"Common Name\" in it's cert against hostname used when connecting. This option is disabled by default.",
+   (gptr*) &opt_ssl_verify_server_cert, (gptr*) &opt_ssl_verify_server_cert,
+    0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
+#endif
 #endif /* HAVE_OPENSSL */

include/sslopt-vars.h

@@ -21,4 +21,7 @@ static char *opt_ssl_cert   = 0;
 static char *opt_ssl_ca     = 0;
 static char *opt_ssl_capath = 0;
 static char *opt_ssl_cipher = 0;
+#ifdef MYSQL_CLIENT
+static my_bool opt_ssl_verify_server_cert= 0;
+#endif
 #endif

sql-common/client.c

@@ -1500,6 +1500,7 @@ mysql_ssl_set(MYSQL *mysql __attribute__((unused)) ,
   mysql->options.ssl_ca=     strdup_if_not_null(ca);
   mysql->options.ssl_capath= strdup_if_not_null(capath);
   mysql->options.ssl_cipher= strdup_if_not_null(cipher);
+  mysql->options.ssl_verify_server_cert= FALSE; /* Off by default */
 #endif /* HAVE_OPENSSL */
   DBUG_RETURN(0);
 }
@@ -1521,7 +1522,7 @@ mysql_ssl_free(MYSQL *mysql __attribute__((unused)))
   my_free(mysql->options.ssl_cert, MYF(MY_ALLOW_ZERO_PTR));
   my_free(mysql->options.ssl_ca, MYF(MY_ALLOW_ZERO_PTR));
   my_free(mysql->options.ssl_capath, MYF(MY_ALLOW_ZERO_PTR));
-  my_free(mysql->options.ssl_cipher, MYF(MY_ALLOW_ZERO_PTR));  
+  my_free(mysql->options.ssl_cipher, MYF(MY_ALLOW_ZERO_PTR));
   if (ssl_fd)
     SSL_CTX_free(ssl_fd->ssl_context);
   my_free(mysql->connector_fd,MYF(MY_ALLOW_ZERO_PTR));
@@ -1534,6 +1535,77 @@ mysql_ssl_free(MYSQL *mysql __attribute__((unused)))
   mysql->connector_fd = 0;
   DBUG_VOID_RETURN;
 }
+
+/*
+  Check the server's (subject) Common Name against the
+  hostname we connected to
+
+  SYNOPSIS
+  ssl_verify_server_cert()
+    vio              pointer to a SSL connected vio
+    server_hostname  name of the server that we connected to
+
+  RETURN VALUES
+   0 Success
+   1 Failed to validate server
+
+ */
+static int ssl_verify_server_cert(Vio *vio, const char* server_hostname)
+{
+  SSL *ssl;
+  X509 *server_cert;
+  char *cp1, *cp2;
+  char buf[256];
+  DBUG_ENTER("ssl_verify_server_cert");
+  DBUG_PRINT("enter", ("server_hostname: %s", server_hostname));
+
+  if (!(ssl= (SSL*)vio->ssl_arg))
+  {
+    DBUG_PRINT("error", ("No SSL pointer found"));
+    DBUG_RETURN(1);
+  }
+
+  if (!server_hostname)
+  {
+    DBUG_PRINT("error", ("No server hostname supplied"));
+    DBUG_RETURN(1);
+  }
+
+  if (!(server_cert= SSL_get_peer_certificate(ssl)))
+  {
+    DBUG_PRINT("error", ("Could not get server certificate"));
+    DBUG_RETURN(1);
+  }
+
+  /*
+    We already know that the certificate exchanged was valid; the SSL library
+    handled that. Now we need to verify that the contents of the certificate
+    are what we expect.
+  */
+
+  X509_NAME_oneline(X509_get_subject_name(server_cert), buf, sizeof(buf));
+  X509_free (server_cert);
+
+  DBUG_PRINT("info", ("hostname in cert: %s", buf));
+  cp1 = strstr(buf, "/CN=");
+  if (cp1)
+  {
+    cp1 += 4; // Skip the "/CN=" that we found
+    // Search for next / which might be the delimiter for email
+    cp2 = strchr(cp1, '/');
+    if (cp2)
+      *cp2 = '\0';
+    DBUG_PRINT("info", ("Server hostname in cert: %s", cp1));
+    if (!strcmp(cp1, server_hostname))
+    {
+      /* Success */
+      DBUG_RETURN(0);
+    }
+  }
+  DBUG_PRINT("error", ("SSL certificate validation failure"));
+  DBUG_RETURN(1);
+}
+
 #endif /* HAVE_OPENSSL */
 
 
@@ -2049,7 +2121,14 @@ CLI_MYSQL_REAL_CONNECT(MYSQL *mysql,const char *host, const char *user,
     }
     DBUG_PRINT("info", ("IO layer change done!"));
 
-    /* TODO Verify server cert */
+    /* Verify server cert */
+    if (mysql->options.ssl_verify_server_cert &&
+        ssl_verify_server_cert(mysql->net.vio, mysql->host))
+    {
+      set_mysql_error(mysql, CR_SSL_CONNECTION_ERROR, unknown_sqlstate);
+      goto error;
+    }
+
   }
 #endif /* HAVE_OPENSSL */
 
@@ -2789,6 +2868,9 @@ mysql_options(MYSQL *mysql,enum mysql_option option, const char *arg)
   case MYSQL_OPT_RECONNECT:
     mysql->reconnect= *(my_bool *) arg;
     break;
+  case MYSQL_OPT_SSL_VERIFY_SERVER_CERT:
+    mysql->options.ssl_verify_server_cert= *(my_bool *) arg;
+    break;
   default:
     DBUG_RETURN(1);
   }

vio/viosslfactories.c

@@ -290,20 +290,20 @@ new_VioSSLConnectorFd(const char *key_file, const char *cert_file,
                       const char *cipher)
 {
   struct st_VioSSLFd *ssl_fd;
-  int verify= SSL_VERIFY_NONE;
+  int verify= SSL_VERIFY_PEER;
   if (!(ssl_fd= new_VioSSLFd(key_file, cert_file, ca_file,
                              ca_path, cipher, TLSv1_client_method())))
   {
     return 0;
   }
+
   /* Init the the VioSSLFd as a "connector" ie. the client side */
 
   /*
     The verify_callback function is used to control the behaviour
-    when the SSL_VERIFY_PEER flag is set. Here it is SSL_VERIFY_NONE
-    and thus callback is set to NULL
+    when the SSL_VERIFY_PEER flag is set.
   */
-  SSL_CTX_set_verify(ssl_fd->ssl_context, verify, NULL);
+  SSL_CTX_set_verify(ssl_fd->ssl_context, verify, vio_verify_callback);
 
   return ssl_fd;
 }