/************************************************* * Exim - an Internet mail transport agent * *************************************************/ /* Copyright (c) University of Cambridge 1995 - 2016 */ /* See the file NOTICE for conditions of use and distribution. */ /* This module provides TLS (aka SSL) support for Exim. The code for OpenSSL is based on a patch that was originally contributed by Steve Haslam. It was adapted from stunnel, a GPL program by Michal Trojnara. The code for GNU TLS is based on a patch contributed by Nikos Mavroyanopoulos. Because these packages are so very different, the functions for each are kept in separate files. The relevant file is #included as required, after any any common functions. No cryptographic code is included in Exim. All this module does is to call functions from the OpenSSL or GNU TLS libraries. */ #include "exim.h" #include "transports/smtp.h" /* This module is compiled only when it is specifically requested in the build-time configuration. However, some compilers don't like compiling empty modules, so keep them happy with a dummy when skipping the rest. Make it reference itself to stop picky compilers complaining that it is unused, and put in a dummy argument to stop even pickier compilers complaining about infinite loops. */ #ifndef SUPPORT_TLS static void dummy(int x) { dummy(x-1); } #else /* Static variables that are used for buffering data by both sets of functions and the common functions below. We're moving away from this; GnuTLS is already using a state, which can switch, so we can do TLS callouts during ACLs. */ static const int ssl_xfer_buffer_size = 4096; #ifndef USE_GNUTLS static uschar *ssl_xfer_buffer = NULL; static int ssl_xfer_buffer_lwm = 0; static int ssl_xfer_buffer_hwm = 0; static int ssl_xfer_eof = 0; static int ssl_xfer_error = 0; #endif uschar *tls_channelbinding_b64 = NULL; /************************************************* * Expand string; give error on failure * *************************************************/ /* If expansion is forced to fail, set the result NULL and return TRUE. Other failures return FALSE. For a server, an SMTP response is given. Arguments: s the string to expand; if NULL just return TRUE name name of string being expanded (for error) result where to put the result Returns: TRUE if OK; result may still be NULL after forced failure */ static BOOL expand_check(const uschar *s, const uschar *name, uschar **result) { if (s == NULL) *result = NULL; else { *result = expand_string(US s); /* need to clean up const some more */ if (*result == NULL && !expand_string_forcedfail) { log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name, expand_string_message); return FALSE; } } return TRUE; } /************************************************* * Timezone environment flipping * *************************************************/ static uschar * to_tz(uschar * tz) { uschar * old = US getenv("TZ"); (void) setenv("TZ", CCS tz, 1); tzset(); return old; } static void restore_tz(uschar * tz) { if (tz) (void) setenv("TZ", CCS tz, 1); else (void) os_unsetenv(US"TZ"); tzset(); } /************************************************* * Many functions are package-specific * *************************************************/ #ifdef USE_GNUTLS # include "tls-gnu.c" # include "tlscert-gnu.c" # define ssl_xfer_buffer (state_server.xfer_buffer) # define ssl_xfer_buffer_lwm (state_server.xfer_buffer_lwm) # define ssl_xfer_buffer_hwm (state_server.xfer_buffer_hwm) # define ssl_xfer_eof (state_server.xfer_eof) # define ssl_xfer_error (state_server.xfer_error) #else # include "tls-openssl.c" # include "tlscert-openssl.c" #endif /************************************************* * TLS version of ungetc * *************************************************/ /* Puts a character back in the input buffer. Only ever called once. Only used by the server-side TLS. Arguments: ch the character Returns: the character */ int tls_ungetc(int ch) { ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch; return ch; } /************************************************* * TLS version of feof * *************************************************/ /* Tests for a previous EOF Only used by the server-side TLS. Arguments: none Returns: non-zero if the eof flag is set */ int tls_feof(void) { return ssl_xfer_eof; } /************************************************* * TLS version of ferror * *************************************************/ /* Tests for a previous read error, and returns with errno restored to what it was when the error was detected. Only used by the server-side TLS. >>>>> Hmm. Errno not handled yet. Where do we get it from? >>>>> Arguments: none Returns: non-zero if the error flag is set */ int tls_ferror(void) { return ssl_xfer_error; } /************************************************* * TLS version of smtp_buffered * *************************************************/ /* Tests for unused chars in the TLS input buffer. Only used by the server-side TLS. Arguments: none Returns: TRUE/FALSE */ BOOL tls_smtp_buffered(void) { return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm; } #endif /* SUPPORT_TLS */ void tls_modify_variables(tls_support * dest_tsp) { modify_variable(US"tls_bits", &dest_tsp->bits); modify_variable(US"tls_certificate_verified", &dest_tsp->certificate_verified); modify_variable(US"tls_cipher", &dest_tsp->cipher); modify_variable(US"tls_peerdn", &dest_tsp->peerdn); #if defined(SUPPORT_TLS) && !defined(USE_GNUTLS) modify_variable(US"tls_sni", &dest_tsp->sni); #endif } #ifdef SUPPORT_TLS /************************************************ * TLS certificate name operations * ************************************************/ /* Convert an rfc4514 DN to an exim comma-sep list. Backslashed commas need to be replaced by doublecomma for Exim's list quoting. We modify the given string inplace. */ static void dn_to_list(uschar * dn) { uschar * cp; for (cp = dn; *cp; cp++) if (cp[0] == '\\' && cp[1] == ',') *cp++ = ','; } /* Extract fields of a given type from an RFC4514- format Distinguished Name. Return an Exim list. NOTE: We modify the supplied dn string during operation. Arguments: dn Distinguished Name string mod list containing optional output list-sep and field selector match, comma-separated Return: allocated string with list of matching fields, field type stripped */ uschar * tls_field_from_dn(uschar * dn, const uschar * mod) { int insep = ','; uschar outsep = '\n'; uschar * ele; uschar * match = NULL; int len; uschar * list = NULL; while ((ele = string_nextinlist(&mod, &insep, NULL, 0))) if (ele[0] != '>') match = ele; /* field tag to match */ else if (ele[1]) outsep = ele[1]; /* nondefault output separator */ dn_to_list(dn); insep = ','; len = match ? Ustrlen(match) : -1; while ((ele = string_nextinlist(CUSS &dn, &insep, NULL, 0))) if ( !match || Ustrncmp(ele, match, len) == 0 && ele[len] == '=' ) list = string_append_listele(list, outsep, ele+len+1); return list; } /* Compare a domain name with a possibly-wildcarded name. Wildcards are restricted to a single one, as the first element of patterns having at least three dot-separated elements. Case-independent. Return TRUE for a match */ static BOOL is_name_match(const uschar * name, const uschar * pat) { uschar * cp; return *pat == '*' /* possible wildcard match */ ? *++pat == '.' /* starts star, dot */ && !Ustrchr(++pat, '*') /* has no more stars */ && Ustrchr(pat, '.') /* and has another dot. */ && (cp = Ustrchr(name, '.'))/* The name has at least one dot */ && strcmpic(++cp, pat) == 0 /* and we only compare after it. */ : !Ustrchr(pat+1, '*') && strcmpic(name, pat) == 0; } /* Compare a list of names with the dnsname elements of the Subject Alternate Name, if any, and the Subject otherwise. Arguments: namelist names to compare cert certificate Returns: TRUE/FALSE */ BOOL tls_is_name_for_cert(const uschar * namelist, void * cert) { uschar * altnames = tls_cert_subject_altname(cert, US"dns"); uschar * subjdn; uschar * certname; int cmp_sep = 0; uschar * cmpname; if ((altnames = tls_cert_subject_altname(cert, US"dns"))) { int alt_sep = '\n'; while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0))) { const uschar * an = altnames; while ((certname = string_nextinlist(&an, &alt_sep, NULL, 0))) if (is_name_match(cmpname, certname)) return TRUE; } } else if ((subjdn = tls_cert_subject(cert, NULL))) { int sn_sep = ','; dn_to_list(subjdn); while ((cmpname = string_nextinlist(&namelist, &cmp_sep, NULL, 0))) { const uschar * sn = subjdn; while ((certname = string_nextinlist(&sn, &sn_sep, NULL, 0))) if ( *certname++ == 'C' && *certname++ == 'N' && *certname++ == '=' && is_name_match(cmpname, certname) ) return TRUE; } } return FALSE; } #endif /*SUPPORT_TLS*/ /* vi: aw ai sw=2 */ /* End of tls.c */