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Diffstat (limited to '')
| -rw-r--r-- | src/auths/heimdal_gssapi.c | 618 |
1 files changed, 618 insertions, 0 deletions
diff --git a/src/auths/heimdal_gssapi.c b/src/auths/heimdal_gssapi.c new file mode 100644 index 0000000..3817632 --- /dev/null +++ b/src/auths/heimdal_gssapi.c @@ -0,0 +1,618 @@ +/************************************************* +* Exim - an Internet mail transport agent * +*************************************************/ + +/* Copyright (c) The Exim Maintainers 2020 - 2022 */ +/* Copyright (c) University of Cambridge 1995 - 2018 */ +/* See the file NOTICE for conditions of use and distribution. */ + +/* Copyright (c) Twitter Inc 2012 + Author: Phil Pennock <pdp@exim.org> */ +/* Copyright (c) Phil Pennock 2012 */ + +/* Interface to Heimdal library for GSSAPI authentication. */ + +/* Naming and rationale + +Sensibly, this integration would be deferred to a SASL library, but none +of them appear to offer keytab file selection interfaces in their APIs. It +might be that this driver only requires minor modification to work with MIT +Kerberos. + +Heimdal provides a number of interfaces for various forms of authentication. +As GS2 does not appear to provide keytab control interfaces either, we may +end up supporting that too. It's possible that we could trivially expand to +support NTLM support via Heimdal, etc. Rather than try to be too generic +immediately, this driver is directly only supporting GSSAPI. + +Without rename, we could add an option for GS2 support in the future. +*/ + +/* Sources + +* mailcheck-imap (Perl, client-side, written by me years ago) +* gsasl driver (GPL, server-side) +* heimdal sources and man-pages, plus http://www.h5l.org/manual/ +* FreeBSD man-pages (very informative!) +* http://www.ggf.org/documents/GFD.24.pdf confirming GSS_KRB5_REGISTER_ACCEPTOR_IDENTITY_X + semantics, that found by browsing Heimdal source to find how to set the keytab; however, + after multiple attempts I failed to get that to work and instead switched to + gsskrb5_register_acceptor_identity(). +*/ + +#include "../exim.h" + +#ifndef AUTH_HEIMDAL_GSSAPI +/* dummy function to satisfy compilers when we link in an "empty" file. */ +static void dummy(int x); +static void dummy2(int x) { dummy(x-1); } +static void dummy(int x) { dummy2(x-1); } +#else + +#include <gssapi/gssapi.h> +#include <gssapi/gssapi_krb5.h> + +/* for the _init debugging */ +#include <krb5.h> + +#include "heimdal_gssapi.h" + +/* Authenticator-specific options. */ +optionlist auth_heimdal_gssapi_options[] = { + { "server_hostname", opt_stringptr, + OPT_OFF(auth_heimdal_gssapi_options_block, server_hostname) }, + { "server_keytab", opt_stringptr, + OPT_OFF(auth_heimdal_gssapi_options_block, server_keytab) }, + { "server_service", opt_stringptr, + OPT_OFF(auth_heimdal_gssapi_options_block, server_service) } +}; + +int auth_heimdal_gssapi_options_count = + sizeof(auth_heimdal_gssapi_options)/sizeof(optionlist); + +/* Defaults for the authenticator-specific options. */ +auth_heimdal_gssapi_options_block auth_heimdal_gssapi_option_defaults = { + US"$primary_hostname", /* server_hostname */ + NULL, /* server_keytab */ + US"smtp", /* server_service */ +}; + + +#ifdef MACRO_PREDEF + +/* Dummy values */ +void auth_heimdal_gssapi_init(auth_instance *ablock) {} +int auth_heimdal_gssapi_server(auth_instance *ablock, uschar *data) {return 0;} +int auth_heimdal_gssapi_client(auth_instance *ablock, void * sx, + int timeout, uschar *buffer, int buffsize) {return 0;} +gstring * auth_heimdal_gssapi_version_report(gstring * g) {} + +#else /*!MACRO_PREDEF*/ + + + +/* "Globals" for managing the heimdal_gssapi interface. */ + +/* Utility functions */ +static void + exim_heimdal_error_debug(const char *, krb5_context, krb5_error_code); +static int + exim_gssapi_error_defer(rmark, OM_uint32, OM_uint32, const char *, ...) + PRINTF_FUNCTION(4, 5); + +#define EmptyBuf(buf) do { buf.value = NULL; buf.length = 0; } while (0) + + +/************************************************* +* Initialization entry point * +*************************************************/ + +/* Called for each instance, after its options have been read, to +enable consistency checks to be done, or anything else that needs +to be set up. */ + +/* Heimdal provides a GSSAPI extension method for setting the keytab; +in the init, we mostly just use raw krb5 methods so that we can report +the keytab contents, for -D+auth debugging. */ + +void +auth_heimdal_gssapi_init(auth_instance *ablock) +{ +krb5_context context; +krb5_keytab keytab; +krb5_kt_cursor cursor; +krb5_keytab_entry entry; +krb5_error_code krc; +char *principal, *enctype_s; +const char *k_keytab_typed_name = NULL; +auth_heimdal_gssapi_options_block *ob = + (auth_heimdal_gssapi_options_block *)(ablock->options_block); + +ablock->server = FALSE; +ablock->client = FALSE; + +if (!ob->server_service || !*ob->server_service) + { + HDEBUG(D_auth) debug_printf("heimdal: missing server_service\n"); + return; + } + +if ((krc = krb5_init_context(&context))) + { + int kerr = errno; + HDEBUG(D_auth) debug_printf("heimdal: failed to initialise krb5 context: %s\n", + strerror(kerr)); + return; + } + +if (ob->server_keytab) + { + k_keytab_typed_name = CCS string_sprintf("file:%s", expand_string(ob->server_keytab)); + HDEBUG(D_auth) debug_printf("heimdal: using keytab %s\n", k_keytab_typed_name); + if ((krc = krb5_kt_resolve(context, k_keytab_typed_name, &keytab))) + { + HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_resolve", context, krc); + return; + } + } +else + { + HDEBUG(D_auth) debug_printf("heimdal: using system default keytab\n"); + if ((krc = krb5_kt_default(context, &keytab))) + { + HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_default", context, krc); + return; + } + } + +HDEBUG(D_auth) + { + /* http://www.h5l.org/manual/HEAD/krb5/krb5_keytab_intro.html */ + if ((krc = krb5_kt_start_seq_get(context, keytab, &cursor))) + exim_heimdal_error_debug("krb5_kt_start_seq_get", context, krc); + else + { + while (!(krc = krb5_kt_next_entry(context, keytab, &entry, &cursor))) + { + principal = enctype_s = NULL; + krb5_unparse_name(context, entry.principal, &principal); + krb5_enctype_to_string(context, entry.keyblock.keytype, &enctype_s); + debug_printf("heimdal: keytab principal: %s vno=%d type=%s\n", + principal ? principal : "??", + entry.vno, + enctype_s ? enctype_s : "??"); + free(principal); + free(enctype_s); + krb5_kt_free_entry(context, &entry); + } + if ((krc = krb5_kt_end_seq_get(context, keytab, &cursor))) + exim_heimdal_error_debug("krb5_kt_end_seq_get", context, krc); + } + } + +if ((krc = krb5_kt_close(context, keytab))) + HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_close", context, krc); + +krb5_free_context(context); + +ablock->server = TRUE; +} + + +static void +exim_heimdal_error_debug(const char *label, + krb5_context context, krb5_error_code err) +{ +const char *kerrsc; +kerrsc = krb5_get_error_message(context, err); +debug_printf("heimdal %s: %s\n", label, kerrsc ? kerrsc : "unknown error"); +krb5_free_error_message(context, kerrsc); +} + +/************************************************* +* Server entry point * +*************************************************/ + +/* For interface, see auths/README */ + +/* GSSAPI notes: +OM_uint32: portable type for unsigned int32 +gss_buffer_desc / *gss_buffer_t: hold/point-to size_t .length & void *value + -- all strings/etc passed in should go through one of these + -- when allocated by gssapi, release with gss_release_buffer() +*/ + +int +auth_heimdal_gssapi_server(auth_instance *ablock, uschar *initial_data) +{ +gss_name_t gclient = GSS_C_NO_NAME; +gss_name_t gserver = GSS_C_NO_NAME; +gss_cred_id_t gcred = GSS_C_NO_CREDENTIAL; +gss_ctx_id_t gcontext = GSS_C_NO_CONTEXT; +uschar *ex_server_str; +gss_buffer_desc gbufdesc = GSS_C_EMPTY_BUFFER; +gss_buffer_desc gbufdesc_in = GSS_C_EMPTY_BUFFER; +gss_buffer_desc gbufdesc_out = GSS_C_EMPTY_BUFFER; +gss_OID mech_type; +OM_uint32 maj_stat, min_stat; +int step, error_out; +uschar *tmp1, *tmp2, *from_client; +auth_heimdal_gssapi_options_block *ob = + (auth_heimdal_gssapi_options_block *)(ablock->options_block); +BOOL handled_empty_ir; +rmark store_reset_point; +uschar *keytab; +uschar sasl_config[4]; +uschar requested_qop; + +store_reset_point = store_mark(); + +HDEBUG(D_auth) + debug_printf("heimdal: initialising auth context for %s\n", ablock->name); + +/* Construct our gss_name_t gserver describing ourselves */ +tmp1 = expand_string(ob->server_service); +tmp2 = expand_string(ob->server_hostname); +ex_server_str = string_sprintf("%s@%s", tmp1, tmp2); +gbufdesc.value = (void *) ex_server_str; +gbufdesc.length = Ustrlen(ex_server_str); +maj_stat = gss_import_name(&min_stat, + &gbufdesc, GSS_C_NT_HOSTBASED_SERVICE, &gserver); +if (GSS_ERROR(maj_stat)) + return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat, + "gss_import_name(%s)", CS gbufdesc.value); + +/* Use a specific keytab, if specified */ +if (ob->server_keytab) + { + keytab = expand_string(ob->server_keytab); + maj_stat = gsskrb5_register_acceptor_identity(CCS keytab); + if (GSS_ERROR(maj_stat)) + return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat, + "registering keytab \"%s\"", keytab); + HDEBUG(D_auth) + debug_printf("heimdal: using keytab \"%s\"\n", keytab); + } + +/* Acquire our credentials */ +maj_stat = gss_acquire_cred(&min_stat, + gserver, /* desired name */ + 0, /* time */ + GSS_C_NULL_OID_SET, /* desired mechs */ + GSS_C_ACCEPT, /* cred usage */ + &gcred, /* handle */ + NULL /* actual mechs */, + NULL /* time rec */); +if (GSS_ERROR(maj_stat)) + return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat, + "gss_acquire_cred(%s)", ex_server_str); + +maj_stat = gss_release_name(&min_stat, &gserver); + +HDEBUG(D_auth) debug_printf("heimdal: have server credentials.\n"); + +/* Loop talking to client */ +step = 0; +from_client = initial_data; +handled_empty_ir = FALSE; +error_out = OK; + +/* buffer sizes: auth_get_data() uses big_buffer, which we grow per +GSSAPI RFC in _init, if needed, to meet the SHOULD size of 64KB. +(big_buffer starts life at the MUST size of 16KB). */ + +/* step values +0: getting initial data from client to feed into GSSAPI +1: iterating for as long as GSS_S_CONTINUE_NEEDED +2: GSS_S_COMPLETE, SASL wrapping for authz and qop to send to client +3: unpick final auth message from client +4: break/finish (non-step) +*/ +while (step < 4) + switch (step) + { + case 0: + if (!from_client || !*from_client) + { + if (handled_empty_ir) + { + HDEBUG(D_auth) debug_printf("gssapi: repeated empty input, grr.\n"); + error_out = BAD64; + goto ERROR_OUT; + } + + HDEBUG(D_auth) debug_printf("gssapi: missing initial response, nudging.\n"); + if ((error_out = auth_get_data(&from_client, US"", 0)) != OK) + goto ERROR_OUT; + handled_empty_ir = TRUE; + continue; + } + /* We should now have the opening data from the client, base64-encoded. */ + step += 1; + HDEBUG(D_auth) debug_printf("heimdal: have initial client data\n"); + break; + + case 1: + gbufdesc_in.length = b64decode(from_client, USS &gbufdesc_in.value); + if (gclient) + { + maj_stat = gss_release_name(&min_stat, &gclient); + gclient = GSS_C_NO_NAME; + } + maj_stat = gss_accept_sec_context(&min_stat, + &gcontext, /* context handle */ + gcred, /* acceptor cred handle */ + &gbufdesc_in, /* input from client */ + GSS_C_NO_CHANNEL_BINDINGS, /* XXX fixme: use the channel bindings from GnuTLS */ + &gclient, /* client identifier */ + &mech_type, /* mechanism in use */ + &gbufdesc_out, /* output to send to client */ + NULL, /* return flags */ + NULL, /* time rec */ + NULL /* delegated cred_handle */ + ); + if (GSS_ERROR(maj_stat)) + { + exim_gssapi_error_defer(NULL, maj_stat, min_stat, + "gss_accept_sec_context()"); + error_out = FAIL; + goto ERROR_OUT; + } + if (gbufdesc_out.length != 0) + { + error_out = auth_get_data(&from_client, + gbufdesc_out.value, gbufdesc_out.length); + if (error_out != OK) + goto ERROR_OUT; + + gss_release_buffer(&min_stat, &gbufdesc_out); + EmptyBuf(gbufdesc_out); + } + if (maj_stat == GSS_S_COMPLETE) + { + step += 1; + HDEBUG(D_auth) debug_printf("heimdal: GSS complete\n"); + } + else + HDEBUG(D_auth) debug_printf("heimdal: need more data\n"); + break; + + case 2: + memset(sasl_config, 0xFF, 4); + /* draft-ietf-sasl-gssapi-06.txt defines bitmasks for first octet + 0x01 No security layer + 0x02 Integrity protection + 0x04 Confidentiality protection + + The remaining three octets are the maximum buffer size for wrapped + content. */ + sasl_config[0] = 0x01; /* Exim does not wrap/unwrap SASL layers after auth */ + gbufdesc.value = (void *) sasl_config; + gbufdesc.length = 4; + maj_stat = gss_wrap(&min_stat, + gcontext, + 0, /* conf_req_flag: integrity only */ + GSS_C_QOP_DEFAULT, /* qop requested */ + &gbufdesc, /* message to protect */ + NULL, /* conf_state: no confidentiality applied */ + &gbufdesc_out /* output buffer */ + ); + if (GSS_ERROR(maj_stat)) + { + exim_gssapi_error_defer(NULL, maj_stat, min_stat, + "gss_wrap(SASL state after auth)"); + error_out = FAIL; + goto ERROR_OUT; + } + + HDEBUG(D_auth) debug_printf("heimdal SASL: requesting QOP with no security layers\n"); + + error_out = auth_get_data(&from_client, + gbufdesc_out.value, gbufdesc_out.length); + if (error_out != OK) + goto ERROR_OUT; + + gss_release_buffer(&min_stat, &gbufdesc_out); + EmptyBuf(gbufdesc_out); + step += 1; + break; + + case 3: + gbufdesc_in.length = b64decode(from_client, USS &gbufdesc_in.value); + maj_stat = gss_unwrap(&min_stat, + gcontext, + &gbufdesc_in, /* data from client */ + &gbufdesc_out, /* results */ + NULL, /* conf state */ + NULL /* qop state */ + ); + if (GSS_ERROR(maj_stat)) + { + exim_gssapi_error_defer(NULL, maj_stat, min_stat, + "gss_unwrap(final SASL message from client)"); + error_out = FAIL; + goto ERROR_OUT; + } + if (gbufdesc_out.length < 4) + { + HDEBUG(D_auth) + debug_printf("gssapi: final message too short; " + "need flags, buf sizes and optional authzid\n"); + error_out = FAIL; + goto ERROR_OUT; + } + + requested_qop = (CS gbufdesc_out.value)[0]; + if (!(requested_qop & 0x01)) + { + HDEBUG(D_auth) + debug_printf("gssapi: client requested security layers (%x)\n", + (unsigned int) requested_qop); + error_out = FAIL; + goto ERROR_OUT; + } + + for (int i = 0; i < AUTH_VARS; i++) auth_vars[i] = NULL; + expand_nmax = 0; + + /* Identifiers: + The SASL provided identifier is an unverified authzid. + GSSAPI provides us with a verified identifier, but it might be empty + for some clients. + */ + + /* $auth2 is authzid requested at SASL layer */ + if (gbufdesc_out.length > 4) + { + expand_nlength[2] = gbufdesc_out.length - 4; + auth_vars[1] = expand_nstring[2] = + string_copyn((US gbufdesc_out.value) + 4, expand_nlength[2]); + expand_nmax = 2; + } + + gss_release_buffer(&min_stat, &gbufdesc_out); + EmptyBuf(gbufdesc_out); + + /* $auth1 is GSSAPI display name */ + maj_stat = gss_display_name(&min_stat, + gclient, &gbufdesc_out, &mech_type); + if (GSS_ERROR(maj_stat)) + { + auth_vars[1] = expand_nstring[2] = NULL; + expand_nmax = 0; + exim_gssapi_error_defer(NULL, maj_stat, min_stat, + "gss_display_name(client identifier)"); + error_out = FAIL; + goto ERROR_OUT; + } + + expand_nlength[1] = gbufdesc_out.length; + auth_vars[0] = expand_nstring[1] = + string_copyn(gbufdesc_out.value, gbufdesc_out.length); + + if (expand_nmax == 0) /* should be: authzid was empty */ + { + expand_nmax = 2; + expand_nlength[2] = expand_nlength[1]; + auth_vars[1] = expand_nstring[2] = string_copyn(expand_nstring[1], expand_nlength[1]); + HDEBUG(D_auth) + debug_printf("heimdal SASL: empty authzid, set to dup of GSSAPI display name\n"); + } + + HDEBUG(D_auth) + debug_printf("heimdal SASL: happy with client request\n" + " auth1 (verified GSSAPI display-name): \"%s\"\n" + " auth2 (unverified SASL requested authzid): \"%s\"\n", + auth_vars[0], auth_vars[1]); + + step += 1; + break; + + } /* switch */ + /* while step */ + + +ERROR_OUT: +maj_stat = gss_release_cred(&min_stat, &gcred); +if (gclient) + { + gss_release_name(&min_stat, &gclient); + gclient = GSS_C_NO_NAME; + } +if (gbufdesc_out.length) + { + gss_release_buffer(&min_stat, &gbufdesc_out); + EmptyBuf(gbufdesc_out); + } +if (gcontext != GSS_C_NO_CONTEXT) + gss_delete_sec_context(&min_stat, &gcontext, GSS_C_NO_BUFFER); + +store_reset(store_reset_point); + +if (error_out != OK) + return error_out; + +/* Auth succeeded, check server_condition */ +return auth_check_serv_cond(ablock); +} + + +static int +exim_gssapi_error_defer(rmark store_reset_point, + OM_uint32 major, OM_uint32 minor, + const char *format, ...) +{ +va_list ap; +OM_uint32 maj_stat, min_stat; +OM_uint32 msgcontext = 0; +gss_buffer_desc status_string; +gstring * g; + +HDEBUG(D_auth) + { + va_start(ap, format); + g = string_vformat(NULL, SVFMT_EXTEND|SVFMT_REBUFFER, format, ap); + va_end(ap); + } + +auth_defer_msg = NULL; + +do { + maj_stat = gss_display_status(&min_stat, + major, GSS_C_GSS_CODE, GSS_C_NO_OID, &msgcontext, &status_string); + + if (!auth_defer_msg) + auth_defer_msg = string_copy(US status_string.value); + + HDEBUG(D_auth) debug_printf("heimdal %s: %.*s\n", + string_from_gstring(g), (int)status_string.length, + CS status_string.value); + gss_release_buffer(&min_stat, &status_string); + + } while (msgcontext != 0); + +if (store_reset_point) + store_reset(store_reset_point); +return DEFER; +} + + +/************************************************* +* Client entry point * +*************************************************/ + +/* For interface, see auths/README */ + +int +auth_heimdal_gssapi_client( + auth_instance *ablock, /* authenticator block */ + void * sx, /* connection */ + int timeout, /* command timeout */ + uschar *buffer, /* buffer for reading response */ + int buffsize) /* size of buffer */ +{ +HDEBUG(D_auth) + debug_printf("Client side NOT IMPLEMENTED: you should not see this!\n"); +/* NOT IMPLEMENTED */ +return FAIL; +} + +/************************************************* +* Diagnostic API * +*************************************************/ + +gstring * +auth_heimdal_gssapi_version_report(gstring * g) +{ +/* No build-time constants available unless we link against libraries at +build-time and export the result as a string into a header ourselves. */ + +return string_fmt_append(g, "Library version: Heimdal: Runtime: %s\n" + " Build Info: %s\n", + heimdal_version, heimdal_long_version)); +} + +#endif /*!MACRO_PREDEF*/ +#endif /* AUTH_HEIMDAL_GSSAPI */ + +/* End of heimdal_gssapi.c */ |