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Diffstat (limited to 'src/tls.c')
| -rw-r--r-- | src/tls.c | 486 |
1 files changed, 486 insertions, 0 deletions
diff --git a/src/tls.c b/src/tls.c new file mode 100644 index 0000000..d37a8f9 --- /dev/null +++ b/src/tls.c @@ -0,0 +1,486 @@ +/************************************************* +* Exim - an Internet mail transport agent * +*************************************************/ + +/* Copyright (c) University of Cambridge 1995 - 2018 */ +/* Copyright (c) The Exim Maintainers 2020 */ +/* 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 Mavrogiannopoulos. 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" + +#if !defined(DISABLE_TLS) && !defined(USE_OPENSSL) && !defined(USE_GNUTLS) +# error One of USE_OPENSSL or USE_GNUTLS must be defined for a TLS build +#endif + + +#if defined(MACRO_PREDEF) && !defined(DISABLE_TLS) +# include "macro_predef.h" +# ifdef USE_GNUTLS +# include "tls-gnu.c" +# else +# include "tls-openssl.c" +# endif +#endif + +#ifndef MACRO_PREDEF + +/* 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. */ + +#ifdef DISABLE_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; +#ifdef USE_OPENSSL +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 = FALSE; +static BOOL ssl_xfer_error = FALSE; +#endif + + +/************************************************* +* 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, uschar ** errstr) +{ +if (!s) + *result = NULL; +else if ( !(*result = expand_string(US s)) /* need to clean up const more */ + && !f.expand_string_forcedfail + ) + { + *errstr = US"Internal error"; + 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) +#endif + +#ifdef USE_OPENSSL +# 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) +{ +if (ssl_xfer_buffer_lwm <= 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc"); + +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 (int)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 (int)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 /*DISABLE_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); +#ifdef USE_OPENSSL +modify_variable(US"tls_sni", &dest_tsp->sni); +#endif +} + + +#ifndef DISABLE_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) +{ +for (uschar * 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; +gstring * 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 string_from_gstring(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; +} + + +/* Environment cleanup: The GnuTLS library uses SSLKEYLOGFILE in the environment +and writes a file by that name. Our OpenSSL code does the same, using keying +info from the library API. +The GnuTLS support only works if exim is run by root, not taking advantage of +the setuid bit. +You can use either the external environment (modulo the keep_environment config) +or the add_environment config option for SSLKEYLOGFILE; the latter takes +precedence. + +If the path is absolute, require it starts with the spooldir; otherwise delete +the env variable. If relative, prefix the spooldir. +*/ +void +tls_clean_env(void) +{ +uschar * path = US getenv("SSLKEYLOGFILE"); +if (path) + if (!*path) + unsetenv("SSLKEYLOGFILE"); + else if (*path != '/') + { + DEBUG(D_tls) + debug_printf("prepending spooldir to env SSLKEYLOGFILE\n"); + setenv("SSLKEYLOGFILE", CCS string_sprintf("%s/%s", spool_directory, path), 1); + } + else if (Ustrncmp(path, spool_directory, Ustrlen(spool_directory)) != 0) + { + DEBUG(D_tls) + debug_printf("removing env SSLKEYLOGFILE=%s: not under spooldir\n", path); + unsetenv("SSLKEYLOGFILE"); + } +} + +/************************************************* +* Drop privs for checking TLS config * +*************************************************/ + +/* We want to validate TLS options during readconf, but do not want to be +root when we call into the TLS library, in case of library linkage errors +which cause segfaults; before this check, those were always done as the Exim +runtime user and it makes sense to continue with that. + +Assumes: tls_require_ciphers has been set, if it will be + exim_user has been set, if it will be + exim_group has been set, if it will be + +Returns: bool for "okay"; false will cause caller to immediately exit. +*/ + +BOOL +tls_dropprivs_validate_require_cipher(BOOL nowarn) +{ +const uschar *errmsg; +pid_t pid; +int rc, status; +void (*oldsignal)(int); + +/* If TLS will never be used, no point checking ciphers */ + +if ( !tls_advertise_hosts + || !*tls_advertise_hosts + || Ustrcmp(tls_advertise_hosts, ":") == 0 + ) + return TRUE; +else if (!nowarn && !tls_certificate) + log_write(0, LOG_MAIN, + "Warning: No server certificate defined; will use a selfsigned one.\n" + " Suggested action: either install a certificate or change tls_advertise_hosts option"); + +oldsignal = signal(SIGCHLD, SIG_DFL); + +fflush(NULL); +if ((pid = exim_fork(US"cipher-validate")) < 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "fork failed for TLS check"); + +if (pid == 0) + { + /* in some modes, will have dropped privilege already */ + if (!geteuid()) + exim_setugid(exim_uid, exim_gid, FALSE, + US"calling tls_validate_require_cipher"); + + if ((errmsg = tls_validate_require_cipher())) + log_write(0, LOG_PANIC_DIE|LOG_CONFIG, + "tls_require_ciphers invalid: %s", errmsg); + fflush(NULL); + exim_underbar_exit(EXIT_SUCCESS); + } + +do { + rc = waitpid(pid, &status, 0); +} while (rc < 0 && errno == EINTR); + +DEBUG(D_tls) + debug_printf("tls_validate_require_cipher child %d ended: status=0x%x\n", + (int)pid, status); + +signal(SIGCHLD, oldsignal); + +return status == 0; +} + + + + +#endif /*!DISABLE_TLS*/ +#endif /*!MACRO_PREDEF*/ + +/* vi: aw ai sw=2 +*/ +/* End of tls.c */ |