1 /* 2 This is an example of how to hook up evhttp with bufferevent_ssl 3 4 It just GETs an https URL given on the command-line and prints the response 5 body to stdout. 6 7 Actually, it also accepts plain http URLs to make it easy to compare http vs 8 https code paths. 9 10 Loosely based on le-proxy.c. 11 */ 12 13 #include <stdio.h> 14 #include <assert.h> 15 #include <stdlib.h> 16 #include <string.h> 17 #include <errno.h> 18 19 #ifdef WIN32 20 #include <winsock2.h> 21 #include <ws2tcpip.h> 22 #else 23 #include <sys/socket.h> 24 #include <netinet/in.h> 25 #endif 26 27 #include <event2/bufferevent_ssl.h> 28 #include <event2/bufferevent.h> 29 #include <event2/buffer.h> 30 #include <event2/listener.h> 31 #include <event2/util.h> 32 #include <event2/http.h> 33 34 #include <openssl/ssl.h> 35 #include <openssl/err.h> 36 #include <openssl/rand.h> 37 38 #include "openssl_hostname_validation.h" 39 40 static struct event_base *base; 41 42 static void 43 http_request_done(struct evhttp_request *req, void *ctx) 44 { 45 char buffer[256]; 46 int nread; 47 48 if (req == NULL) { 49 /* If req is NULL, it means an error occurred, but 50 * sadly we are mostly left guessing what the error 51 * might have been. We'll do our best... */ 52 struct bufferevent *bev = (struct bufferevent *) ctx; 53 unsigned long oslerr; 54 int printed_err = 0; 55 int errcode = EVUTIL_SOCKET_ERROR(); 56 fprintf(stderr, "some request failed - no idea which one though!\n"); 57 /* Print out the OpenSSL error queue that libevent 58 * squirreled away for us, if any. */ 59 while ((oslerr = bufferevent_get_openssl_error(bev))) { 60 ERR_error_string_n(oslerr, buffer, sizeof(buffer)); 61 fprintf(stderr, "%s\n", buffer); 62 printed_err = 1; 63 } 64 /* If the OpenSSL error queue was empty, maybe it was a 65 * socket error; let's try printing that. */ 66 if (! printed_err) 67 fprintf(stderr, "socket error = %s (%d)\n", 68 evutil_socket_error_to_string(errcode), 69 errcode); 70 return; 71 } 72 73 fprintf(stderr, "Response line: %d %s\n", 74 evhttp_request_get_response_code(req), 75 evhttp_request_get_response_code_line(req)); 76 77 while ((nread = evbuffer_remove(evhttp_request_get_input_buffer(req), 78 buffer, sizeof(buffer))) 79 > 0) { 80 /* These are just arbitrary chunks of 256 bytes. 81 * They are not lines, so we can't treat them as such. */ 82 fwrite(buffer, nread, 1, stdout); 83 } 84 } 85 86 static void 87 syntax(void) 88 { 89 fputs("Syntax:\n", stderr); 90 fputs(" https-client <https-url>\n", stderr); 91 fputs("Example:\n", stderr); 92 fputs(" https-client https://ip.appspot.com/\n", stderr); 93 94 exit(1); 95 } 96 97 static void 98 die(const char *msg) 99 { 100 fputs(msg, stderr); 101 exit(1); 102 } 103 104 static void 105 die_openssl(const char *func) 106 { 107 fprintf (stderr, "%s failed:\n", func); 108 109 /* This is the OpenSSL function that prints the contents of the 110 * error stack to the specified file handle. */ 111 ERR_print_errors_fp (stderr); 112 113 exit(1); 114 } 115 116 /* See http://archives.seul.org/libevent/users/Jan-2013/msg00039.html */ 117 static int cert_verify_callback(X509_STORE_CTX *x509_ctx, void *arg) 118 { 119 char cert_str[256]; 120 const char *host = (const char *) arg; 121 const char *res_str = "X509_verify_cert failed"; 122 HostnameValidationResult res = Error; 123 124 /* This is the function that OpenSSL would call if we hadn't called 125 * SSL_CTX_set_cert_verify_callback(). Therefore, we are "wrapping" 126 * the default functionality, rather than replacing it. */ 127 int ok_so_far = X509_verify_cert(x509_ctx); 128 129 X509 *server_cert = X509_STORE_CTX_get_current_cert(x509_ctx); 130 131 if (ok_so_far) { 132 res = validate_hostname(host, server_cert); 133 134 switch (res) { 135 case MatchFound: 136 res_str = "MatchFound"; 137 break; 138 case MatchNotFound: 139 res_str = "MatchNotFound"; 140 break; 141 case NoSANPresent: 142 res_str = "NoSANPresent"; 143 break; 144 case MalformedCertificate: 145 res_str = "MalformedCertificate"; 146 break; 147 case Error: 148 res_str = "Error"; 149 break; 150 default: 151 res_str = "WTF!"; 152 break; 153 } 154 } 155 156 X509_NAME_oneline(X509_get_subject_name (server_cert), 157 cert_str, sizeof (cert_str)); 158 159 if (res == MatchFound) { 160 printf("https server '%s' has this certificate, " 161 "which looks good to me:\n%s\n", 162 host, cert_str); 163 return 1; 164 } else { 165 printf("Got '%s' for hostname '%s' and certificate:\n%s\n", 166 res_str, host, cert_str); 167 return 0; 168 } 169 } 170 171 int 172 main(int argc, char **argv) 173 { 174 int r; 175 176 struct evhttp_uri *http_uri; 177 const char *url, *scheme, *host, *path, *query; 178 char uri[256]; 179 int port; 180 181 SSL_CTX *ssl_ctx; 182 SSL *ssl; 183 struct bufferevent *bev; 184 struct evhttp_connection *evcon; 185 struct evhttp_request *req; 186 struct evkeyvalq *output_headers; 187 188 if (argc != 2) 189 syntax(); 190 191 url = argv[1]; 192 http_uri = evhttp_uri_parse(url); 193 if (http_uri == NULL) { 194 die("malformed url"); 195 } 196 197 scheme = evhttp_uri_get_scheme(http_uri); 198 if (scheme == NULL || (strcasecmp(scheme, "https") != 0 && 199 strcasecmp(scheme, "http") != 0)) { 200 die("url must be http or https"); 201 } 202 203 host = evhttp_uri_get_host(http_uri); 204 if (host == NULL) { 205 die("url must have a host"); 206 } 207 208 port = evhttp_uri_get_port(http_uri); 209 if (port == -1) { 210 port = (strcasecmp(scheme, "http") == 0) ? 80 : 443; 211 } 212 213 path = evhttp_uri_get_path(http_uri); 214 if (path == NULL) { 215 path = "/"; 216 } 217 218 query = evhttp_uri_get_query(http_uri); 219 if (query == NULL) { 220 snprintf(uri, sizeof(uri) - 1, "%s", path); 221 } else { 222 snprintf(uri, sizeof(uri) - 1, "%s?%s", path, query); 223 } 224 uri[sizeof(uri) - 1] = '\0'; 225 226 // Initialize OpenSSL 227 SSL_library_init(); 228 ERR_load_crypto_strings(); 229 SSL_load_error_strings(); 230 OpenSSL_add_all_algorithms(); 231 232 /* This isn't strictly necessary... OpenSSL performs RAND_poll 233 * automatically on first use of random number generator. */ 234 r = RAND_poll(); 235 if (r == 0) { 236 die_openssl("RAND_poll"); 237 } 238 239 /* Create a new OpenSSL context */ 240 ssl_ctx = SSL_CTX_new(SSLv23_method()); 241 if (!ssl_ctx) 242 die_openssl("SSL_CTX_new"); 243 244 /* Attempt to use the system's trusted root certificates. 245 * (This path is only valid for Debian-based systems.) */ 246 if (1 != SSL_CTX_load_verify_locations(ssl_ctx, 247 "/etc/ssl/certs/ca-certificates.crt", 248 NULL)) 249 die_openssl("SSL_CTX_load_verify_locations"); 250 /* Ask OpenSSL to verify the server certificate. Note that this 251 * does NOT include verifying that the hostname is correct. 252 * So, by itself, this means anyone with any legitimate 253 * CA-issued certificate for any website, can impersonate any 254 * other website in the world. This is not good. See "The 255 * Most Dangerous Code in the World" article at 256 * https://crypto.stanford.edu/~dabo/pubs/abstracts/ssl-client-bugs.html 257 */ 258 SSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_PEER, NULL); 259 /* This is how we solve the problem mentioned in the previous 260 * comment. We "wrap" OpenSSL's validation routine in our 261 * own routine, which also validates the hostname by calling 262 * the code provided by iSECPartners. Note that even though 263 * the "Everything You've Always Wanted to Know About 264 * Certificate Validation With OpenSSL (But Were Afraid to 265 * Ask)" paper from iSECPartners says very explicitly not to 266 * call SSL_CTX_set_cert_verify_callback (at the bottom of 267 * page 2), what we're doing here is safe because our 268 * cert_verify_callback() calls X509_verify_cert(), which is 269 * OpenSSL's built-in routine which would have been called if 270 * we hadn't set the callback. Therefore, we're just 271 * "wrapping" OpenSSL's routine, not replacing it. */ 272 SSL_CTX_set_cert_verify_callback (ssl_ctx, cert_verify_callback, 273 (void *) host); 274 275 // Create event base 276 base = event_base_new(); 277 if (!base) { 278 perror("event_base_new()"); 279 return 1; 280 } 281 282 // Create OpenSSL bufferevent and stack evhttp on top of it 283 ssl = SSL_new(ssl_ctx); 284 if (ssl == NULL) { 285 die_openssl("SSL_new()"); 286 } 287 288 if (strcasecmp(scheme, "http") == 0) { 289 bev = bufferevent_socket_new(base, -1, BEV_OPT_CLOSE_ON_FREE); 290 } else { 291 bev = bufferevent_openssl_socket_new(base, -1, ssl, 292 BUFFEREVENT_SSL_CONNECTING, 293 BEV_OPT_CLOSE_ON_FREE|BEV_OPT_DEFER_CALLBACKS); 294 } 295 296 if (bev == NULL) { 297 fprintf(stderr, "bufferevent_openssl_socket_new() failed\n"); 298 return 1; 299 } 300 301 bufferevent_openssl_set_allow_dirty_shutdown(bev, 1); 302 303 // For simplicity, we let DNS resolution block. Everything else should be 304 // asynchronous though. 305 evcon = evhttp_connection_base_bufferevent_new(base, NULL, bev, 306 host, port); 307 if (evcon == NULL) { 308 fprintf(stderr, "evhttp_connection_base_bufferevent_new() failed\n"); 309 return 1; 310 } 311 312 // Fire off the request 313 req = evhttp_request_new(http_request_done, bev); 314 if (req == NULL) { 315 fprintf(stderr, "evhttp_request_new() failed\n"); 316 return 1; 317 } 318 319 output_headers = evhttp_request_get_output_headers(req); 320 evhttp_add_header(output_headers, "Host", host); 321 evhttp_add_header(output_headers, "Connection", "close"); 322 323 r = evhttp_make_request(evcon, req, EVHTTP_REQ_GET, uri); 324 if (r != 0) { 325 fprintf(stderr, "evhttp_make_request() failed\n"); 326 return 1; 327 } 328 329 event_base_dispatch(base); 330 331 evhttp_connection_free(evcon); 332 event_base_free(base); 333 334 return 0; 335 } 336