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