1 /* $NetBSD: verify_sender_addr.c,v 1.4 2022/10/08 16:12:45 christos Exp $ */ 2 3 /*++ 4 /* NAME 5 /* verify_sender_addr 3 6 /* SUMMARY 7 /* time-dependent probe sender addresses 8 /* SYNOPSIS 9 /* #include <verify_sender_addr.h> 10 /* 11 /* char *var_verify_sender; 12 /* int var_verify_sender_ttl; 13 /* 14 /* const char *make_verify_sender_addr() 15 /* 16 /* const char *valid_verify_sender_addr(addr) 17 /* const char *addr; 18 /* DESCRIPTION 19 /* This module computes or verifies a constant or time-dependent 20 /* sender address for an address verification probe. The 21 /* time-dependent portion is appended to the address localpart 22 /* specified with the address_verify_sender parameter. 23 /* 24 /* When the address_verify_sender parameter is empty or <>, 25 /* the sender address is always the empty address (i.e. always 26 /* time-independent). 27 /* 28 /* The caller must initialize the address_verify_sender and 29 /* address_verify_sender_ttl parameter values. 30 /* 31 /* make_verify_sender_addr() generates an envelope sender 32 /* address for an address verification probe. 33 /* 34 /* valid_verify_sender_addr() verifies that the given address 35 /* is a valid sender address for address verification probes. 36 /* When probe sender addresses are configured to be time-dependent, 37 /* the given address is allowed to differ by +/-1 TTL unit 38 /* from the expected address. The result is a null pointer 39 /* when no match is found. Otherwise, the result is the sender 40 /* address without the time-dependent portion; this is the 41 /* address that should be used for further delivery. 42 /* DIAGNOSTICS 43 /* Fatal errors: malformed address_verify_sender value; out 44 /* of memory. 45 /* LICENSE 46 /* .ad 47 /* .fi 48 /* The Secure Mailer license must be distributed with this software. 49 /* AUTHOR(S) 50 /* Wietse Venema 51 /* IBM T.J. Watson Research 52 /* P.O. Box 704 53 /* Yorktown Heights, NY 10598, USA 54 /*--*/ 55 56 /* System library. */ 57 58 #include <sys_defs.h> 59 #include <errno.h> 60 #include <string.h> 61 #include <stdlib.h> 62 63 /* Utility library. */ 64 65 #include <msg.h> 66 #include <vstring.h> 67 #include <events.h> 68 #include <stringops.h> 69 70 /* Global library */ 71 72 #include <mail_params.h> 73 #include <rewrite_clnt.h> 74 #include <safe_ultostr.h> 75 #include <verify_sender_addr.h> 76 77 /* Application-specific. */ 78 79 /* 80 * We convert the time-dependent portion to a safe string (no vowels) in a 81 * reversible manner, so that we can check an incoming address against the 82 * current and +/-1 TTL time slot. This allows for some time slippage 83 * between multiple MTAs that handle mail for the same site. We use base 31 84 * so that the time stamp contains B-Z0-9. This simplifies regression tests. 85 */ 86 #define VERIFY_BASE 31 87 88 /* 89 * We append the time-dependent portion to the localpart of the address 90 * verification probe sender address, so that the result has the form 91 * ``fixed1variable@fixed2''. There is no delimiter between ``fixed1'' and 92 * ``variable'', because that could make "old" time stamps valid depending 93 * on how the recipient_delimiter feature is configured. The fixed text is 94 * taken from var_verify_sender with perhaps domain information appended 95 * during address canonicalization. The variable part of the address changes 96 * every var_verify_sender_ttl seconds. 97 */ 98 char *var_verify_sender; /* "bare" probe sender address */ 99 int var_verify_sender_ttl; /* time between address changes */ 100 101 /* 102 * Scaffolding for stand-alone testing. 103 */ 104 #ifdef TEST 105 #undef event_time 106 #define event_time() verify_time 107 static unsigned long verify_time; 108 109 #endif 110 111 #define VERIFY_SENDER_ADDR_EPOCH() (event_time() / var_verify_sender_ttl) 112 113 /* 114 * SLMs. 115 */ 116 #define STR(x) vstring_str(x) 117 #define LEN(x) VSTRING_LEN(x) 118 119 /* make_verify_sender_addr - generate address_verify_sender address */ 120 121 const char *make_verify_sender_addr(void) 122 { 123 static VSTRING *verify_sender_buf; /* the complete sender address */ 124 static VSTRING *my_epoch_buf; /* scratch space */ 125 char *my_at_domain; 126 127 /* 128 * The null sender is always time-independent. 129 */ 130 if (*var_verify_sender == 0 || strcmp(var_verify_sender, "<>") == 0) 131 return (""); 132 133 /* 134 * Sanity check. 135 */ 136 if (*var_verify_sender == '@') 137 msg_fatal("parameter %s: value \"%s\" must not start with '@'", 138 VAR_VERIFY_SENDER, var_verify_sender); 139 if ((my_at_domain = strchr(var_verify_sender, '@')) != 0 && my_at_domain[1] == 0) 140 msg_fatal("parameter %s: value \"%s\" must not end with '@'", 141 VAR_VERIFY_SENDER, var_verify_sender); 142 143 /* 144 * One-time initialization. 145 */ 146 if (verify_sender_buf == 0) { 147 verify_sender_buf = vstring_alloc(10); 148 my_epoch_buf = vstring_alloc(10); 149 } 150 151 /* 152 * Start with the bare sender address. 153 */ 154 vstring_strcpy(verify_sender_buf, var_verify_sender); 155 156 /* 157 * Append the time stamp to the address localpart, encoded in some 158 * non-decimal form for obscurity. 159 * 160 * XXX It would be nice to have safe_ultostr() append-only support. 161 */ 162 if (var_verify_sender_ttl > 0) { 163 /* Strip the @domain portion, if applicable. */ 164 if (my_at_domain != 0) 165 vstring_truncate(verify_sender_buf, 166 (ssize_t) (my_at_domain - var_verify_sender)); 167 /* Append the time stamp to the address localpart. */ 168 vstring_sprintf_append(verify_sender_buf, "%s", 169 safe_ultostr(my_epoch_buf, 170 VERIFY_SENDER_ADDR_EPOCH(), 171 VERIFY_BASE, 0, 0)); 172 /* Add back the @domain, if applicable. */ 173 if (my_at_domain != 0) 174 vstring_sprintf_append(verify_sender_buf, "%s", my_at_domain); 175 } 176 177 /* 178 * Rewrite the address to canonical form. 179 */ 180 rewrite_clnt_internal(MAIL_ATTR_RWR_LOCAL, STR(verify_sender_buf), 181 verify_sender_buf); 182 183 return (STR(verify_sender_buf)); 184 } 185 186 /* valid_verify_sender_addr - decide if address matches time window +/-1 */ 187 188 const char *valid_verify_sender_addr(const char *their_addr) 189 { 190 static VSTRING *time_indep_sender_buf; /* sender without time stamp */ 191 ssize_t base_len; 192 unsigned long my_epoch; 193 unsigned long their_epoch; 194 char *my_at_domain; 195 char *their_at_domain; 196 char *cp; 197 198 /* 199 * The null address is always time-independent. 200 */ 201 if (*var_verify_sender == 0 || strcmp(var_verify_sender, "<>") == 0) 202 return (*their_addr ? 0 : ""); 203 204 /* 205 * One-time initialization. Generate the time-independent address that we 206 * will return if the match is successful. This address is also used as a 207 * matching template. 208 */ 209 if (time_indep_sender_buf == 0) { 210 time_indep_sender_buf = vstring_alloc(10); 211 vstring_strcpy(time_indep_sender_buf, var_verify_sender); 212 rewrite_clnt_internal(MAIL_ATTR_RWR_LOCAL, STR(time_indep_sender_buf), 213 time_indep_sender_buf); 214 } 215 216 /* 217 * Check the time-independent sender localpart. 218 */ 219 if ((my_at_domain = strchr(STR(time_indep_sender_buf), '@')) != 0) 220 base_len = my_at_domain - STR(time_indep_sender_buf); 221 else 222 base_len = LEN(time_indep_sender_buf); 223 if (strncasecmp_utf8(STR(time_indep_sender_buf), their_addr, base_len) != 0) 224 return (0); /* sender localpart mis-match */ 225 226 /* 227 * Check the time-independent domain. 228 */ 229 if ((their_at_domain = strchr(their_addr, '@')) == 0 && my_at_domain != 0) 230 return (0); /* sender domain mis-match */ 231 if (their_at_domain != 0 232 && (my_at_domain == 0 233 || strcasecmp_utf8(their_at_domain, my_at_domain) != 0)) 234 return (0); /* sender domain mis-match */ 235 236 /* 237 * Check the time-dependent portion. 238 */ 239 if (var_verify_sender_ttl > 0) { 240 their_epoch = safe_strtoul(their_addr + base_len, &cp, VERIFY_BASE); 241 if ((*cp != '@' && *cp != 0) 242 || (their_epoch == ULONG_MAX && errno == ERANGE)) 243 return (0); /* malformed time stamp */ 244 my_epoch = VERIFY_SENDER_ADDR_EPOCH(); 245 if (their_epoch < my_epoch - 1 || their_epoch > my_epoch + 1) 246 return (0); /* outside time window */ 247 } 248 249 /* 250 * No time-dependent portion. 251 */ 252 else { 253 if (their_addr[base_len] != '@' && their_addr[base_len] != 0) 254 return (0); /* garbage after sender base */ 255 } 256 return (STR(time_indep_sender_buf)); 257 } 258 259 /* 260 * Proof-of-concept test program. Read test address_verify_sender and 261 * address_verify_sender_ttl values from stdin, and report results that we 262 * would get on stdout. 263 */ 264 #ifdef TEST 265 266 #include <stdlib.h> 267 #include <vstream.h> 268 #include <msg_vstream.h> 269 #include <vstring_vstream.h> 270 #include <mail_conf.h> 271 #include <conv_time.h> 272 273 int main(int argc, char **argv) 274 { 275 const char *verify_sender; 276 const char *valid_sender; 277 278 msg_vstream_init(argv[0], VSTREAM_ERR); 279 280 /* 281 * Prepare to talk to the address rewriting service. 282 */ 283 mail_conf_read(); 284 vstream_printf("using config files in %s\n", var_config_dir); 285 if (chdir(var_queue_dir) < 0) 286 msg_fatal("chdir %s: %m", var_queue_dir); 287 288 /* 289 * Parse JCL. 290 */ 291 if (argc != 3) 292 msg_fatal("usage: %s address_verify_sender address_verify_sender_ttl", 293 argv[0]); 294 var_verify_sender = argv[1]; 295 if (conv_time(argv[2], &var_verify_sender_ttl, 's') == 0) 296 msg_fatal("bad time value: %s", argv[2]); 297 verify_time = time((time_t *) 0); 298 299 /* 300 * Compute the current probe sender address. 301 */ 302 verify_sender = make_verify_sender_addr(); 303 304 /* 305 * Check two past time slots. 306 */ 307 if (var_verify_sender_ttl > 0) { 308 verify_time -= 2 * var_verify_sender_ttl; 309 vstream_printf("\"%s\" matches prev2: \"%s\"\n", verify_sender, 310 (valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ? 311 valid_sender : "nope"); 312 verify_time += var_verify_sender_ttl; 313 vstream_printf("\"%s\" matches prev1: \"%s\"\n", verify_sender, 314 (valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ? 315 valid_sender : "nope"); 316 verify_time += var_verify_sender_ttl; 317 } 318 319 /* 320 * Check the current time slot. 321 */ 322 vstream_printf("\"%s\" matches self: \"%s\"\n", verify_sender, 323 (valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ? 324 valid_sender : "nope"); 325 326 /* 327 * Check two future time slots. 328 */ 329 if (var_verify_sender_ttl > 0) { 330 verify_time += var_verify_sender_ttl; 331 vstream_printf("\"%s\" matches next1: \"%s\"\n", verify_sender, 332 (valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ? 333 valid_sender : "nope"); 334 verify_time += var_verify_sender_ttl; 335 vstream_printf("\"%s\" matches next2: \"%s\"\n", verify_sender, 336 (valid_sender = valid_verify_sender_addr(verify_sender)) != 0 ? 337 valid_sender : "nope"); 338 } 339 vstream_fflush(VSTREAM_OUT); 340 exit(0); 341 } 342 343 #endif 344
Indexes created Sat Oct 10 00:27:21 UTC 2026