471 lines
11 KiB
C
471 lines
11 KiB
C
/**
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* FreeRDP: A Remote Desktop Protocol Implementation
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* Transport Layer Security
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*
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* Copyright 2011-2012 Marc-Andre Moreau <marcandre.moreau@gmail.com>
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <freerdp/utils/stream.h>
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#include <freerdp/utils/memory.h>
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#include <freerdp/crypto/tls.h>
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static CryptoCert tls_get_certificate(rdpTls* tls)
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{
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CryptoCert cert;
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X509* server_cert;
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server_cert = SSL_get_peer_certificate(tls->ssl);
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if (!server_cert)
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{
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printf("ssl_verify: failed to get the server SSL certificate\n");
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cert = NULL;
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}
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else
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{
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cert = xmalloc(sizeof(*cert));
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cert->px509 = server_cert;
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}
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return cert;
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}
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static void tls_free_certificate(CryptoCert cert)
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{
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X509_free(cert->px509);
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xfree(cert);
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}
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boolean tls_connect(rdpTls* tls)
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{
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CryptoCert cert;
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int connection_status;
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tls->ctx = SSL_CTX_new(TLSv1_client_method());
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if (tls->ctx == NULL)
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{
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printf("SSL_CTX_new failed\n");
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return false;
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}
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/*
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* This is necessary, because the Microsoft TLS implementation is not perfect.
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* SSL_OP_ALL enables a couple of workarounds for buggy TLS implementations,
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* but the most important workaround being SSL_OP_TLS_BLOCK_PADDING_BUG.
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* As the size of the encrypted payload may give hints about its contents,
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* block padding is normally used, but the Microsoft TLS implementation
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* won't recognize it and will disconnect you after sending a TLS alert.
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*/
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SSL_CTX_set_options(tls->ctx, SSL_OP_ALL);
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tls->ssl = SSL_new(tls->ctx);
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if (tls->ssl == NULL)
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{
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SSL_CTX_free(tls->ctx);
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printf("SSL_new failed\n");
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return false;
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}
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if (SSL_set_fd(tls->ssl, tls->sockfd) < 1)
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{
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SSL_free(tls->ssl);
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SSL_CTX_free(tls->ctx);
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printf("SSL_set_fd failed\n");
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return false;
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}
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connection_status = SSL_connect(tls->ssl);
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if (connection_status <= 0)
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{
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if (tls_print_error("SSL_connect", tls->ssl, connection_status))
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{
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SSL_free(tls->ssl);
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SSL_CTX_free(tls->ctx);
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return false;
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}
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}
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cert = tls_get_certificate(tls);
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if (cert == NULL)
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{
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printf("tls_connect: tls_get_certificate failed to return the server certificate.\n");
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return false;
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}
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if (!crypto_cert_get_public_key(cert, &tls->public_key))
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{
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printf("tls_connect: crypto_cert_get_public_key failed to return the server public key.\n");
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return false;
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}
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if (!tls_verify_certificate(tls, cert, tls->settings->hostname))
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tls_disconnect(tls);
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tls_free_certificate(cert);
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return true;
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}
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boolean tls_accept(rdpTls* tls, const char* cert_file, const char* privatekey_file)
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{
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int connection_status;
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tls->ctx = SSL_CTX_new(TLSv1_server_method());
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if (tls->ctx == NULL)
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{
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printf("SSL_CTX_new failed\n");
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return false;
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}
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if (SSL_CTX_use_RSAPrivateKey_file(tls->ctx, privatekey_file, SSL_FILETYPE_PEM) <= 0)
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{
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printf("SSL_CTX_use_RSAPrivateKey_file failed\n");
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return false;
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}
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tls->ssl = SSL_new(tls->ctx);
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if (tls->ssl == NULL)
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{
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printf("SSL_new failed\n");
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return false;
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}
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if (SSL_use_certificate_file(tls->ssl, cert_file, SSL_FILETYPE_PEM) <= 0)
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{
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printf("SSL_use_certificate_file failed\n");
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return false;
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}
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if (SSL_set_fd(tls->ssl, tls->sockfd) < 1)
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{
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printf("SSL_set_fd failed\n");
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return false;
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}
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connection_status = SSL_accept(tls->ssl);
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if (connection_status <= 0)
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{
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if (tls_print_error("SSL_accept", tls->ssl, connection_status))
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return false;
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}
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printf("TLS connection accepted\n");
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return true;
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}
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boolean tls_disconnect(rdpTls* tls)
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{
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SSL_shutdown(tls->ssl);
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return true;
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}
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int tls_read(rdpTls* tls, uint8* data, int length)
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{
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int status;
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status = SSL_read(tls->ssl, data, length);
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switch (SSL_get_error(tls->ssl, status))
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{
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case SSL_ERROR_NONE:
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break;
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case SSL_ERROR_WANT_READ:
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case SSL_ERROR_WANT_WRITE:
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status = 0;
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break;
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default:
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tls_print_error("SSL_read", tls->ssl, status);
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status = -1;
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break;
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}
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return status;
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}
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int tls_write(rdpTls* tls, uint8* data, int length)
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{
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int status;
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status = SSL_write(tls->ssl, data, length);
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switch (SSL_get_error(tls->ssl, status))
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{
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case SSL_ERROR_NONE:
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break;
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case SSL_ERROR_WANT_READ:
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case SSL_ERROR_WANT_WRITE:
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status = 0;
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break;
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default:
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tls_print_error("SSL_write", tls->ssl, status);
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status = -1;
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break;
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}
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return status;
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}
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boolean tls_print_error(char* func, SSL* connection, int value)
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{
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switch (SSL_get_error(connection, value))
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{
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case SSL_ERROR_ZERO_RETURN:
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printf("%s: Server closed TLS connection\n", func);
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return true;
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case SSL_ERROR_WANT_READ:
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printf("SSL_ERROR_WANT_READ\n");
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return false;
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case SSL_ERROR_WANT_WRITE:
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printf("SSL_ERROR_WANT_WRITE\n");
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return false;
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case SSL_ERROR_SYSCALL:
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printf("%s: I/O error\n", func);
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return true;
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case SSL_ERROR_SSL:
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printf("%s: Failure in SSL library (protocol error?)\n", func);
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return true;
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default:
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printf("%s: Unknown error\n", func);
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return true;
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}
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}
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boolean tls_verify_certificate(rdpTls* tls, CryptoCert cert, char* hostname)
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{
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int match;
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int index;
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char* common_name;
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int common_name_length;
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char** alt_names;
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int alt_names_count;
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int* alt_names_lengths;
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boolean certificate_status;
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boolean hostname_match = false;
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rdpCertificateData* certificate_data;
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/* ignore certificate verification if user explicitly required it (discouraged) */
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if (tls->settings->ignore_certificate)
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return true; /* success! */
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/* if user explicitly specified a certificate name, use it instead of the hostname */
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if (tls->settings->certificate_name)
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hostname = tls->settings->certificate_name;
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/* attempt verification using OpenSSL and the ~/.freerdp/certs certificate store */
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certificate_status = x509_verify_certificate(cert, tls->certificate_store->path);
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/* verify certificate name match */
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certificate_data = crypto_get_certificate_data(cert->px509, hostname);
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/* extra common name and alternative names */
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common_name = crypto_cert_subject_common_name(cert->px509, &common_name_length);
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alt_names = crypto_cert_subject_alt_name(cert->px509, &alt_names_count, &alt_names_lengths);
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/* compare against common name */
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if (common_name != NULL)
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{
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if (strlen(hostname) == common_name_length)
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{
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if (memcmp((void*) hostname, (void*) common_name, common_name_length) == 0)
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hostname_match = true;
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}
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}
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/* compare against alternative names */
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if (alt_names != NULL)
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{
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for (index = 0; index < alt_names_count; index++)
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{
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if (strlen(hostname) == alt_names_lengths[index])
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{
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if (memcmp((void*) hostname, (void*) alt_names[index], alt_names_lengths[index]) == 0)
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hostname_match = true;
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}
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}
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}
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/* if the certificate is valid and the certificate name matches, verification succeeds */
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if (certificate_status && hostname_match)
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return true; /* success! */
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/* if the certificate is valid but the certificate name does not match, warn user, do not accept */
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if (certificate_status && !hostname_match)
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tls_print_certificate_name_mismatch_error(hostname, common_name, alt_names, alt_names_count);
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/* verification could not succeed with OpenSSL, use known_hosts file and prompt user for manual verification */
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if (!certificate_status)
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{
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char* issuer;
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char* subject;
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char* fingerprint;
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boolean accept_certificate = false;
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boolean verification_status = false;
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issuer = crypto_cert_issuer(cert->px509);
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subject = crypto_cert_subject(cert->px509);
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fingerprint = crypto_cert_fingerprint(cert->px509);
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/* search for matching entry in known_hosts file */
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match = certificate_data_match(tls->certificate_store, certificate_data);
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if (match == 1)
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{
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/* no entry was found in known_hosts file, prompt user for manual verification */
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freerdp* instance = (freerdp*) tls->settings->instance;
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if (!hostname_match)
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tls_print_certificate_name_mismatch_error(hostname, common_name, alt_names, alt_names_count);
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if (instance->VerifyCertificate)
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accept_certificate = instance->VerifyCertificate(instance, subject, issuer, fingerprint);
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if (!accept_certificate)
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{
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/* user did not accept, abort and do not add entry in known_hosts file */
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verification_status = false; /* failure! */
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}
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else
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{
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/* user accepted certificate, add entry in known_hosts file */
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certificate_data_print(tls->certificate_store, certificate_data);
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verification_status = true; /* success! */
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}
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}
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else if (match == -1)
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{
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/* entry was found in known_hosts file, but fingerprint does not match */
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tls_print_certificate_error(hostname, fingerprint);
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verification_status = false; /* failure! */
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}
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else if (match == 0)
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{
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verification_status = true; /* success! */
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}
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xfree(issuer);
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xfree(subject);
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xfree(fingerprint);
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return verification_status;
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}
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return false;
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}
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void tls_print_certificate_error(char* hostname, char* fingerprint)
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{
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printf("The host key for %s has changed\n", hostname);
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printf("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n");
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printf("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @\n");
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printf("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n");
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printf("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!\n");
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printf("Someone could be eavesdropping on you right now (man-in-the-middle attack)!\n");
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printf("It is also possible that a host key has just been changed.\n");
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printf("The fingerprint for the host key sent by the remote host is\n%s\n", fingerprint);
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printf("Please contact your system administrator.\n");
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printf("Add correct host key in ~/.freerdp/known_hosts to get rid of this message.\n");
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printf("Host key for %s has changed and you have requested strict checking.\n", hostname);
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printf("Host key verification failed.\n");
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}
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void tls_print_certificate_name_mismatch_error(char* hostname, char* common_name, char** alt_names, int alt_names_count)
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{
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int index;
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printf("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n");
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printf("@ WARNING: CERTIFICATE NAME MISMATCH! @\n");
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printf("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n");
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printf("The hostname used for this connection (%s) \n", hostname);
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if (alt_names_count < 1)
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{
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printf("does not match the name given in the certificate:\n");
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printf("%s\n", common_name);
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}
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else
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{
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printf("does not match the names given in the certificate:\n");
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printf("%s", common_name);
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for (index = 0; index < alt_names_count; index++)
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{
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printf(", %s", alt_names[index]);
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}
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printf("\n");
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}
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printf("A valid certificate for the wrong name should NOT be trusted!\n");
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}
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rdpTls* tls_new(rdpSettings* settings)
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{
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rdpTls* tls;
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tls = (rdpTls*) xzalloc(sizeof(rdpTls));
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if (tls != NULL)
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{
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SSL_load_error_strings();
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SSL_library_init();
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tls->settings = settings;
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tls->certificate_store = certificate_store_new(settings);
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}
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return tls;
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}
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void tls_free(rdpTls* tls)
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{
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if (tls != NULL)
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{
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if (tls->ssl)
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SSL_free(tls->ssl);
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if (tls->ctx)
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SSL_CTX_free(tls->ctx);
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freerdp_blob_free(&tls->public_key);
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certificate_store_free(tls->certificate_store);
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xfree(tls);
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}
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}
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