1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2018 */
6 /* Copyright (c) The Exim Maintainers 2020 */
7 /* See the file NOTICE for conditions of use and distribution. */
9 /* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is
10 based on a patch that was originally contributed by Steve Haslam. It was
11 adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is
12 based on a patch contributed by Nikos Mavrogiannopoulos. Because these packages
13 are so very different, the functions for each are kept in separate files. The
14 relevant file is #included as required, after any any common functions.
16 No cryptographic code is included in Exim. All this module does is to call
17 functions from the OpenSSL or GNU TLS libraries. */
21 #include "transports/smtp.h"
23 #if !defined(DISABLE_TLS) && !defined(USE_OPENSSL) && !defined(USE_GNUTLS)
24 # error One of USE_OPENSSL or USE_GNUTLS must be defined for a TLS build
28 #if defined(MACRO_PREDEF) && !defined(DISABLE_TLS)
29 # include "macro_predef.h"
33 # include "tls-openssl.c"
39 static void tls_per_lib_daemon_init(void);
40 static void tls_per_lib_daemon_tick(void);
41 static void tls_server_creds_init(void);
42 static void tls_server_creds_invalidate(void);
43 static void tls_client_creds_init(transport_instance *, BOOL);
44 static void tls_client_creds_invalidate(transport_instance *);
45 static void tls_daemon_creds_reload(void);
46 static BOOL opt_set_and_noexpand(const uschar *);
47 static BOOL opt_unset_or_noexpand(const uschar *);
51 /* This module is compiled only when it is specifically requested in the
52 build-time configuration. However, some compilers don't like compiling empty
53 modules, so keep them happy with a dummy when skipping the rest. Make it
54 reference itself to stop picky compilers complaining that it is unused, and put
55 in a dummy argument to stop even pickier compilers complaining about infinite
59 static void dummy(int x) { dummy(x-1); }
60 #else /* most of the rest of the file */
62 const exim_tlslib_state null_tls_preload = {0};
64 /* Static variables that are used for buffering data by both sets of
65 functions and the common functions below.
67 We're moving away from this; GnuTLS is already using a state, which
68 can switch, so we can do TLS callouts during ACLs. */
70 static const int ssl_xfer_buffer_size = 4096;
72 static uschar *ssl_xfer_buffer = NULL;
73 static int ssl_xfer_buffer_lwm = 0;
74 static int ssl_xfer_buffer_hwm = 0;
75 static int ssl_xfer_eof = FALSE;
76 static BOOL ssl_xfer_error = FALSE;
79 #ifdef EXIM_HAVE_KEVENT
80 # define KEV_SIZE 16 /* Eight file,dir pairs */
81 static struct kevent kev[KEV_SIZE];
82 static int kev_used = 0;
85 /*************************************************
86 * Expand string; give error on failure *
87 *************************************************/
89 /* If expansion is forced to fail, set the result NULL and return TRUE.
90 Other failures return FALSE. For a server, an SMTP response is given.
93 s the string to expand; if NULL just return TRUE
94 name name of string being expanded (for error)
95 result where to put the result
97 Returns: TRUE if OK; result may still be NULL after forced failure
101 expand_check(const uschar *s, const uschar *name, uschar **result, uschar ** errstr)
105 else if ( !(*result = expand_string(US s)) /* need to clean up const more */
106 && !f.expand_string_forcedfail
109 *errstr = US"Internal error";
110 log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
111 expand_string_message);
118 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
119 /* Add the directory for a filename to the inotify handle, creating that if
120 needed. This is enough to see changes to files in that dir.
121 Return boolean success.
123 The word "system" fails, which is on the safe side as we don't know what
124 directory it implies nor if the TLS library handles a watch for us.
126 The string "system,cache" is recognised and explicitly accepted without
127 setting a watch. This permits the system CA bundle to be cached even though
128 we have no way to tell when it gets modified by an update.
129 The call chain for OpenSSL uses a (undocumented) call into the library
130 to discover the actual file. We don't know what GnuTLS uses.
132 A full set of caching including the CAs takes 35ms output off of the
133 server tls_init() (GnuTLS, Fedora 32, 2018-class x86_64 laptop hardware).
136 tls_set_one_watch(const uschar * filename)
137 # ifdef EXIM_HAVE_INOTIFY
141 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
143 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
144 s = string_copyn(filename, s - filename); /* mem released by tls_set_watch */
145 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
147 /*XXX unclear what effect symlinked files will have for inotify */
149 if (inotify_add_watch(tls_watch_fd, CCS s,
150 IN_ONESHOT | IN_CLOSE_WRITE | IN_DELETE | IN_DELETE_SELF
151 | IN_MOVED_FROM | IN_MOVED_TO | IN_MOVE_SELF) >= 0)
153 DEBUG(D_tls) debug_printf("add_watch: %s\n", strerror(errno));
157 # ifdef EXIM_HAVE_KEVENT
160 int fd1, fd2, i, cnt = 0;
163 if (Ustrcmp(filename, "system,cache") == 0) return TRUE;
167 if (!(s = Ustrrchr(filename, '/'))) return FALSE;
168 if ((lstat(filename, &sb)) < 0) return FALSE;
169 if (kev_used > KEV_SIZE-2) return FALSE;
171 /* The dir open will fail if there is a symlink on the path. Fine; it's too
172 much effort to handle all possible cases; just refuse the preload. */
174 if ((fd2 = open(s, O_RDONLY | O_NOFOLLOW)) < 0) return FALSE;
176 if (!S_ISLNK(sb.st_mode))
178 if ((fd1 = open(filename, O_RDONLY | O_NOFOLLOW)) < 0) return FALSE;
179 DEBUG(D_tls) debug_printf("watch file '%s'\n", filename);
180 EV_SET(&kev[++kev_used],
183 EV_ADD | EV_ENABLE | EV_ONESHOT,
184 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
185 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
190 DEBUG(D_tls) debug_printf("watch dir '%s'\n", s);
191 EV_SET(&kev[++kev_used],
194 EV_ADD | EV_ENABLE | EV_ONESHOT,
195 NOTE_DELETE | NOTE_WRITE | NOTE_EXTEND
196 | NOTE_ATTRIB | NOTE_RENAME | NOTE_REVOKE,
201 if (!(S_ISLNK(sb.st_mode))) break;
203 s = store_get(1024, FALSE);
204 if ((i = readlink(filename, s, 1024)) < 0) return FALSE;
207 store_release_above(s+1);
210 if (kevent(tls_watch_fd, &kev[kev_used-cnt], cnt, NULL, 0, NULL) >= 0)
212 DEBUG(D_tls) debug_printf("add_watch: %d, %s\n", strerror(errno));
215 # endif /*EXIM_HAVE_KEVENT*/
218 /* Create an inotify facility if needed.
219 Then set watches on the dir containing the given file or (optionally)
220 list of files. Return boolean success. */
223 tls_set_watch(const uschar * filename, BOOL list)
228 if (!filename || !*filename) return TRUE;
229 if (Ustrncmp(filename, "system", 6) == 0) return TRUE;
231 DEBUG(D_tls) debug_printf("tls_set_watch: '%s'\n", filename);
233 if ( tls_watch_fd < 0
234 # ifdef EXIM_HAVE_INOTIFY
235 && (tls_watch_fd = inotify_init1(O_CLOEXEC)) < 0
237 # ifdef EXIM_HAVE_KEVENT
238 && (tls_watch_fd = kqueue()) < 0
242 DEBUG(D_tls) debug_printf("inotify_init: %s\n", strerror(errno));
251 for (uschar * s; s = string_nextinlist(&filename, &sep, NULL, 0); )
252 if (!(rc = tls_set_one_watch(s))) break;
255 rc = tls_set_one_watch(filename);
258 if (!rc) DEBUG(D_tls) debug_printf("tls_set_watch() fail on '%s': %s\n", filename, strerror(errno));
264 tls_watch_discard_event(int fd)
266 #ifdef EXIM_HAVE_INOTIFY
267 (void) read(fd, big_buffer, big_buffer_size);
269 #ifdef EXIM_HAVE_KEVENT
271 struct timespec t = {0};
272 (void) kevent(fd, NULL, 0, &kev, 1, &t);
276 /* Called, after a delay for multiple file ops to get done, from
277 the daemon when any of the watches added (above) fire.
279 Dump the set of watches and arrange to reload cached creds (which
280 will set up new watches). */
283 tls_watch_triggered(void)
285 DEBUG(D_tls) debug_printf("watch triggered\n");
287 tls_daemon_creds_reload();
289 #endif /*EXIM_HAVE_INOTIFY*/
293 tls_client_creds_reload(BOOL watch)
295 for(transport_instance * t = transports; t; t = t->next)
296 if (Ustrcmp(t->driver_name, "smtp") == 0)
298 tls_client_creds_invalidate(t);
299 tls_client_creds_init(t, watch);
305 tls_watch_invalidate(void)
307 if (tls_watch_fd < 0) return;
309 #ifdef EXIM_HAVE_KEVENT
310 /* Close the files we had open for kevent */
311 for (int fd, i = 0; i < kev_used; i++)
313 (void) close((int) kev[i].ident);
314 kev[i].ident = (uintptr_t)-1;
325 tls_daemon_creds_reload(void)
327 #ifdef EXIM_HAVE_KEVENT
328 tls_watch_invalidate();
331 tls_server_creds_invalidate();
332 tls_server_creds_init();
334 tls_client_creds_reload(TRUE);
338 /* Utility predicates for use by the per-library code */
340 opt_set_and_noexpand(const uschar * opt)
341 { return opt && *opt && Ustrchr(opt, '$') == NULL; }
344 opt_unset_or_noexpand(const uschar * opt)
345 { return !opt || Ustrchr(opt, '$') == NULL; }
349 /* Called every time round the daemon loop */
352 tls_daemon_tick(void)
354 tls_per_lib_daemon_tick();
355 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
356 if (tls_watch_trigger_time && time(NULL) >= tls_watch_trigger_time + 5)
358 tls_watch_trigger_time = 0;
359 tls_watch_triggered();
364 /* Called once at daemon startup */
367 tls_daemon_init(void)
369 tls_per_lib_daemon_init();
373 /*************************************************
374 * Timezone environment flipping *
375 *************************************************/
380 uschar * old = US getenv("TZ");
381 (void) setenv("TZ", CCS tz, 1);
387 restore_tz(uschar * tz)
390 (void) setenv("TZ", CCS tz, 1);
392 (void) os_unsetenv(US"TZ");
396 /*************************************************
397 * Many functions are package-specific *
398 *************************************************/
401 # include "tls-gnu.c"
402 # include "tlscert-gnu.c"
403 # define ssl_xfer_buffer (state_server.xfer_buffer)
404 # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm)
405 # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm)
406 # define ssl_xfer_eof (state_server.xfer_eof)
407 # define ssl_xfer_error (state_server.xfer_error)
411 # include "tls-openssl.c"
412 # include "tlscert-openssl.c"
417 /*************************************************
418 * TLS version of ungetc *
419 *************************************************/
421 /* Puts a character back in the input buffer. Only ever
423 Only used by the server-side TLS.
428 Returns: the character
434 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
440 /*************************************************
441 * TLS version of feof *
442 *************************************************/
444 /* Tests for a previous EOF
445 Only used by the server-side TLS.
448 Returns: non-zero if the eof flag is set
454 return (int)ssl_xfer_eof;
459 /*************************************************
460 * TLS version of ferror *
461 *************************************************/
463 /* Tests for a previous read error, and returns with errno
464 restored to what it was when the error was detected.
465 Only used by the server-side TLS.
467 >>>>> Hmm. Errno not handled yet. Where do we get it from? >>>>>
470 Returns: non-zero if the error flag is set
476 return (int)ssl_xfer_error;
480 /*************************************************
481 * TLS version of smtp_buffered *
482 *************************************************/
484 /* Tests for unused chars in the TLS input buffer.
485 Only used by the server-side TLS.
492 tls_smtp_buffered(void)
494 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
498 #endif /*DISABLE_TLS*/
501 tls_modify_variables(tls_support * dest_tsp)
503 modify_variable(US"tls_bits", &dest_tsp->bits);
504 modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified);
505 modify_variable(US"tls_cipher", &dest_tsp->cipher);
506 modify_variable(US"tls_peerdn", &dest_tsp->peerdn);
508 modify_variable(US"tls_sni", &dest_tsp->sni);
514 /************************************************
515 * TLS certificate name operations *
516 ************************************************/
518 /* Convert an rfc4514 DN to an exim comma-sep list.
519 Backslashed commas need to be replaced by doublecomma
520 for Exim's list quoting. We modify the given string
525 dn_to_list(uschar * dn)
527 for (uschar * cp = dn; *cp; cp++)
528 if (cp[0] == '\\' && cp[1] == ',')
533 /* Extract fields of a given type from an RFC4514-
534 format Distinguished Name. Return an Exim list.
535 NOTE: We modify the supplied dn string during operation.
538 dn Distinguished Name string
539 mod list containing optional output list-sep and
540 field selector match, comma-separated
542 allocated string with list of matching fields,
547 tls_field_from_dn(uschar * dn, const uschar * mod)
550 uschar outsep = '\n';
552 uschar * match = NULL;
554 gstring * list = NULL;
556 while ((ele = string_nextinlist(&mod, &insep, NULL, 0)))
558 match = ele; /* field tag to match */
560 outsep = ele[1]; /* nondefault output separator */
564 len = match ? Ustrlen(match) : -1;
565 while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0)))
567 || Ustrncmp(ele, match, len) == 0 && ele[len] == '='
569 list = string_append_listele(list, outsep, ele+len+1);
570 return string_from_gstring(list);
574 /* Compare a domain name with a possibly-wildcarded name. Wildcards
575 are restricted to a single one, as the first element of patterns
576 having at least three dot-separated elements. Case-independent.
577 Return TRUE for a match
580 is_name_match(const uschar * name, const uschar * pat)
583 return *pat == '*' /* possible wildcard match */
584 ? *++pat == '.' /* starts star, dot */
585 && !Ustrchr(++pat, '*') /* has no more stars */
586 && Ustrchr(pat, '.') /* and has another dot. */
587 && (cp = Ustrchr(name, '.'))/* The name has at least one dot */
588 && strcmpic(++cp, pat) == 0 /* and we only compare after it. */
589 : !Ustrchr(pat+1, '*')
590 && strcmpic(name, pat) == 0;
593 /* Compare a list of names with the dnsname elements
594 of the Subject Alternate Name, if any, and the
598 namelist names to compare
606 tls_is_name_for_cert(const uschar * namelist, void * cert)
608 uschar * altnames = tls_cert_subject_altname(cert, US"dns");
614 if ((altnames = tls_cert_subject_altname(cert, US"dns")))
617 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
619 const uschar * an = altnames;
620 while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0)))
621 if (is_name_match(cmpname, certname))
626 else if ((subjdn = tls_cert_subject(cert, NULL)))
631 while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0)))
633 const uschar * sn = subjdn;
634 while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0)))
635 if ( *certname++ == 'C'
636 && *certname++ == 'N'
637 && *certname++ == '='
638 && is_name_match(cmpname, certname)
647 /* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment
648 and writes a file by that name. Our OpenSSL code does the same, using keying
649 info from the library API.
650 The GnuTLS support only works if exim is run by root, not taking advantage of
652 You can use either the external environment (modulo the keep_environment config)
653 or the add_environment config option for SSLKEYLOGFILE; the latter takes
656 If the path is absolute, require it starts with the spooldir; otherwise delete
657 the env variable. If relative, prefix the spooldir.
662 uschar * path = US getenv("SSLKEYLOGFILE");
665 unsetenv("SSLKEYLOGFILE");
666 else if (*path != '/')
669 debug_printf("prepending spooldir to env SSLKEYLOGFILE\n");
670 setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1);
672 else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0)
675 debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path);
676 unsetenv("SSLKEYLOGFILE");
680 /*************************************************
681 * Drop privs for checking TLS config *
682 *************************************************/
684 /* We want to validate TLS options during readconf, but do not want to be
685 root when we call into the TLS library, in case of library linkage errors
686 which cause segfaults; before this check, those were always done as the Exim
687 runtime user and it makes sense to continue with that.
689 Assumes: tls_require_ciphers has been set, if it will be
690 exim_user has been set, if it will be
691 exim_group has been set, if it will be
693 Returns: bool for "okay"; false will cause caller to immediately exit.
697 tls_dropprivs_validate_require_cipher(BOOL nowarn)
699 const uschar *errmsg;
702 void (*oldsignal)(int);
704 /* If TLS will never be used, no point checking ciphers */
706 if ( !tls_advertise_hosts
707 || !*tls_advertise_hosts
708 || Ustrcmp(tls_advertise_hosts, ":") == 0
711 else if (!nowarn && !tls_certificate)
712 log_write(0, LOG_MAIN,
713 "Warning: No server certificate defined; will use a selfsigned one.\n"
714 " Suggested action: either install a certificate or change tls_advertise_hosts option");
716 oldsignal = signal(SIGCHLD, SIG_DFL);
719 if ((pid = exim_fork(US"cipher-validate")) < 0)
720 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check");
724 /* in some modes, will have dropped privilege already */
726 exim_setugid(exim_uid, exim_gid, FALSE,
727 US"calling tls_validate_require_cipher");
729 if ((errmsg = tls_validate_require_cipher()))
730 log_write(0, LOG_PANIC_DIE|LOG_CONFIG,
731 "tls_require_ciphers invalid: %s", errmsg);
733 exim_underbar_exit(EXIT_SUCCESS);
737 rc = waitpid(pid, &status, 0);
738 } while (rc < 0 && errno == EINTR);
741 debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n",
744 signal(SIGCHLD, oldsignal);
752 #endif /*!DISABLE_TLS*/
753 #endif /*!MACRO_PREDEF*/