diff options
author | Simon Wilkinson <simon@sxw.org.uk> | 2014-02-09 16:09:48 +0000 |
---|---|---|
committer | Colin Watson <cjwatson@debian.org> | 2017-10-04 13:54:43 +0100 |
commit | 4e70490950e5c5134df48848affaf73685bf0284 (patch) | |
tree | 59de097e770693fb1f81268e85f7802df32cb58e /sshconnect2.c | |
parent | 62f54f20bf351468e0124f63cc2902ee40d9b0e9 (diff) |
GSSAPI key exchange support
This patch has been rejected upstream: "None of the OpenSSH developers are
in favour of adding this, and this situation has not changed for several
years. This is not a slight on Simon's patch, which is of fine quality, but
just that a) we don't trust GSSAPI implementations that much and b) we don't
like adding new KEX since they are pre-auth attack surface. This one is
particularly scary, since it requires hooks out to typically root-owned
system resources."
However, quite a lot of people rely on this in Debian, and it's better to
have it merged into the main openssh package rather than having separate
-krb5 packages (as we used to have). It seems to have a generally good
security history.
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242
Last-Updated: 2017-10-04
Patch-Name: gssapi.patch
Diffstat (limited to 'sshconnect2.c')
-rw-r--r-- | sshconnect2.c | 131 |
1 files changed, 127 insertions, 4 deletions
diff --git a/sshconnect2.c b/sshconnect2.c index be9397e48..c22477f59 100644 --- a/sshconnect2.c +++ b/sshconnect2.c | |||
@@ -162,6 +162,11 @@ ssh_kex2(char *host, struct sockaddr *hostaddr, u_short port) | |||
162 | struct kex *kex; | 162 | struct kex *kex; |
163 | int r; | 163 | int r; |
164 | 164 | ||
165 | #ifdef GSSAPI | ||
166 | char *orig = NULL, *gss = NULL; | ||
167 | char *gss_host = NULL; | ||
168 | #endif | ||
169 | |||
165 | xxx_host = host; | 170 | xxx_host = host; |
166 | xxx_hostaddr = hostaddr; | 171 | xxx_hostaddr = hostaddr; |
167 | 172 | ||
@@ -192,6 +197,35 @@ ssh_kex2(char *host, struct sockaddr *hostaddr, u_short port) | |||
192 | order_hostkeyalgs(host, hostaddr, port)); | 197 | order_hostkeyalgs(host, hostaddr, port)); |
193 | } | 198 | } |
194 | 199 | ||
200 | #ifdef GSSAPI | ||
201 | if (options.gss_keyex) { | ||
202 | /* Add the GSSAPI mechanisms currently supported on this | ||
203 | * client to the key exchange algorithm proposal */ | ||
204 | orig = myproposal[PROPOSAL_KEX_ALGS]; | ||
205 | |||
206 | if (options.gss_server_identity) | ||
207 | gss_host = xstrdup(options.gss_server_identity); | ||
208 | else if (options.gss_trust_dns) | ||
209 | gss_host = remote_hostname(active_state); | ||
210 | else | ||
211 | gss_host = xstrdup(host); | ||
212 | |||
213 | gss = ssh_gssapi_client_mechanisms(gss_host, | ||
214 | options.gss_client_identity); | ||
215 | if (gss) { | ||
216 | debug("Offering GSSAPI proposal: %s", gss); | ||
217 | xasprintf(&myproposal[PROPOSAL_KEX_ALGS], | ||
218 | "%s,%s", gss, orig); | ||
219 | |||
220 | /* If we've got GSSAPI algorithms, then we also | ||
221 | * support the 'null' hostkey, as a last resort */ | ||
222 | orig = myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS]; | ||
223 | xasprintf(&myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS], | ||
224 | "%s,null", orig); | ||
225 | } | ||
226 | } | ||
227 | #endif | ||
228 | |||
195 | if (options.rekey_limit || options.rekey_interval) | 229 | if (options.rekey_limit || options.rekey_interval) |
196 | packet_set_rekey_limits(options.rekey_limit, | 230 | packet_set_rekey_limits(options.rekey_limit, |
197 | options.rekey_interval); | 231 | options.rekey_interval); |
@@ -213,15 +247,41 @@ ssh_kex2(char *host, struct sockaddr *hostaddr, u_short port) | |||
213 | # endif | 247 | # endif |
214 | #endif | 248 | #endif |
215 | kex->kex[KEX_C25519_SHA256] = kexc25519_client; | 249 | kex->kex[KEX_C25519_SHA256] = kexc25519_client; |
250 | #ifdef GSSAPI | ||
251 | if (options.gss_keyex) { | ||
252 | kex->kex[KEX_GSS_GRP1_SHA1] = kexgss_client; | ||
253 | kex->kex[KEX_GSS_GRP14_SHA1] = kexgss_client; | ||
254 | kex->kex[KEX_GSS_GEX_SHA1] = kexgss_client; | ||
255 | } | ||
256 | #endif | ||
216 | kex->client_version_string=client_version_string; | 257 | kex->client_version_string=client_version_string; |
217 | kex->server_version_string=server_version_string; | 258 | kex->server_version_string=server_version_string; |
218 | kex->verify_host_key=&verify_host_key_callback; | 259 | kex->verify_host_key=&verify_host_key_callback; |
219 | 260 | ||
261 | #ifdef GSSAPI | ||
262 | if (options.gss_keyex) { | ||
263 | kex->gss_deleg_creds = options.gss_deleg_creds; | ||
264 | kex->gss_trust_dns = options.gss_trust_dns; | ||
265 | kex->gss_client = options.gss_client_identity; | ||
266 | kex->gss_host = gss_host; | ||
267 | } | ||
268 | #endif | ||
269 | |||
220 | ssh_dispatch_run_fatal(active_state, DISPATCH_BLOCK, &kex->done); | 270 | ssh_dispatch_run_fatal(active_state, DISPATCH_BLOCK, &kex->done); |
221 | 271 | ||
222 | /* remove ext-info from the KEX proposals for rekeying */ | 272 | /* remove ext-info from the KEX proposals for rekeying */ |
223 | myproposal[PROPOSAL_KEX_ALGS] = | 273 | myproposal[PROPOSAL_KEX_ALGS] = |
224 | compat_kex_proposal(options.kex_algorithms); | 274 | compat_kex_proposal(options.kex_algorithms); |
275 | #ifdef GSSAPI | ||
276 | /* repair myproposal after it was crumpled by the */ | ||
277 | /* ext-info removal above */ | ||
278 | if (gss) { | ||
279 | orig = myproposal[PROPOSAL_KEX_ALGS]; | ||
280 | xasprintf(&myproposal[PROPOSAL_KEX_ALGS], | ||
281 | "%s,%s", gss, orig); | ||
282 | free(gss); | ||
283 | } | ||
284 | #endif | ||
225 | if ((r = kex_prop2buf(kex->my, myproposal)) != 0) | 285 | if ((r = kex_prop2buf(kex->my, myproposal)) != 0) |
226 | fatal("kex_prop2buf: %s", ssh_err(r)); | 286 | fatal("kex_prop2buf: %s", ssh_err(r)); |
227 | 287 | ||
@@ -311,6 +371,7 @@ int input_gssapi_token(int type, u_int32_t, struct ssh *); | |||
311 | int input_gssapi_hash(int type, u_int32_t, struct ssh *); | 371 | int input_gssapi_hash(int type, u_int32_t, struct ssh *); |
312 | int input_gssapi_error(int, u_int32_t, struct ssh *); | 372 | int input_gssapi_error(int, u_int32_t, struct ssh *); |
313 | int input_gssapi_errtok(int, u_int32_t, struct ssh *); | 373 | int input_gssapi_errtok(int, u_int32_t, struct ssh *); |
374 | int userauth_gsskeyex(Authctxt *authctxt); | ||
314 | #endif | 375 | #endif |
315 | 376 | ||
316 | void userauth(Authctxt *, char *); | 377 | void userauth(Authctxt *, char *); |
@@ -327,6 +388,11 @@ static char *authmethods_get(void); | |||
327 | 388 | ||
328 | Authmethod authmethods[] = { | 389 | Authmethod authmethods[] = { |
329 | #ifdef GSSAPI | 390 | #ifdef GSSAPI |
391 | {"gssapi-keyex", | ||
392 | userauth_gsskeyex, | ||
393 | NULL, | ||
394 | &options.gss_authentication, | ||
395 | NULL}, | ||
330 | {"gssapi-with-mic", | 396 | {"gssapi-with-mic", |
331 | userauth_gssapi, | 397 | userauth_gssapi, |
332 | NULL, | 398 | NULL, |
@@ -654,25 +720,40 @@ userauth_gssapi(Authctxt *authctxt) | |||
654 | static u_int mech = 0; | 720 | static u_int mech = 0; |
655 | OM_uint32 min; | 721 | OM_uint32 min; |
656 | int ok = 0; | 722 | int ok = 0; |
723 | char *gss_host; | ||
724 | |||
725 | if (options.gss_server_identity) | ||
726 | gss_host = xstrdup(options.gss_server_identity); | ||
727 | else if (options.gss_trust_dns) | ||
728 | gss_host = remote_hostname(active_state); | ||
729 | else | ||
730 | gss_host = xstrdup(authctxt->host); | ||
657 | 731 | ||
658 | /* Try one GSSAPI method at a time, rather than sending them all at | 732 | /* Try one GSSAPI method at a time, rather than sending them all at |
659 | * once. */ | 733 | * once. */ |
660 | 734 | ||
661 | if (gss_supported == NULL) | 735 | if (gss_supported == NULL) |
662 | gss_indicate_mechs(&min, &gss_supported); | 736 | if (GSS_ERROR(gss_indicate_mechs(&min, &gss_supported))) { |
737 | gss_supported = NULL; | ||
738 | free(gss_host); | ||
739 | return 0; | ||
740 | } | ||
663 | 741 | ||
664 | /* Check to see if the mechanism is usable before we offer it */ | 742 | /* Check to see if the mechanism is usable before we offer it */ |
665 | while (mech < gss_supported->count && !ok) { | 743 | while (mech < gss_supported->count && !ok) { |
666 | /* My DER encoding requires length<128 */ | 744 | /* My DER encoding requires length<128 */ |
667 | if (gss_supported->elements[mech].length < 128 && | 745 | if (gss_supported->elements[mech].length < 128 && |
668 | ssh_gssapi_check_mechanism(&gssctxt, | 746 | ssh_gssapi_check_mechanism(&gssctxt, |
669 | &gss_supported->elements[mech], authctxt->host)) { | 747 | &gss_supported->elements[mech], gss_host, |
748 | options.gss_client_identity)) { | ||
670 | ok = 1; /* Mechanism works */ | 749 | ok = 1; /* Mechanism works */ |
671 | } else { | 750 | } else { |
672 | mech++; | 751 | mech++; |
673 | } | 752 | } |
674 | } | 753 | } |
675 | 754 | ||
755 | free(gss_host); | ||
756 | |||
676 | if (!ok) | 757 | if (!ok) |
677 | return 0; | 758 | return 0; |
678 | 759 | ||
@@ -763,8 +844,8 @@ input_gssapi_response(int type, u_int32_t plen, struct ssh *ssh) | |||
763 | { | 844 | { |
764 | Authctxt *authctxt = ssh->authctxt; | 845 | Authctxt *authctxt = ssh->authctxt; |
765 | Gssctxt *gssctxt; | 846 | Gssctxt *gssctxt; |
766 | int oidlen; | 847 | u_int oidlen; |
767 | char *oidv; | 848 | u_char *oidv; |
768 | 849 | ||
769 | if (authctxt == NULL) | 850 | if (authctxt == NULL) |
770 | fatal("input_gssapi_response: no authentication context"); | 851 | fatal("input_gssapi_response: no authentication context"); |
@@ -877,6 +958,48 @@ input_gssapi_error(int type, u_int32_t plen, struct ssh *ssh) | |||
877 | free(lang); | 958 | free(lang); |
878 | return 0; | 959 | return 0; |
879 | } | 960 | } |
961 | |||
962 | int | ||
963 | userauth_gsskeyex(Authctxt *authctxt) | ||
964 | { | ||
965 | Buffer b; | ||
966 | gss_buffer_desc gssbuf; | ||
967 | gss_buffer_desc mic = GSS_C_EMPTY_BUFFER; | ||
968 | OM_uint32 ms; | ||
969 | |||
970 | static int attempt = 0; | ||
971 | if (attempt++ >= 1) | ||
972 | return (0); | ||
973 | |||
974 | if (gss_kex_context == NULL) { | ||
975 | debug("No valid Key exchange context"); | ||
976 | return (0); | ||
977 | } | ||
978 | |||
979 | ssh_gssapi_buildmic(&b, authctxt->server_user, authctxt->service, | ||
980 | "gssapi-keyex"); | ||
981 | |||
982 | gssbuf.value = buffer_ptr(&b); | ||
983 | gssbuf.length = buffer_len(&b); | ||
984 | |||
985 | if (GSS_ERROR(ssh_gssapi_sign(gss_kex_context, &gssbuf, &mic))) { | ||
986 | buffer_free(&b); | ||
987 | return (0); | ||
988 | } | ||
989 | |||
990 | packet_start(SSH2_MSG_USERAUTH_REQUEST); | ||
991 | packet_put_cstring(authctxt->server_user); | ||
992 | packet_put_cstring(authctxt->service); | ||
993 | packet_put_cstring(authctxt->method->name); | ||
994 | packet_put_string(mic.value, mic.length); | ||
995 | packet_send(); | ||
996 | |||
997 | buffer_free(&b); | ||
998 | gss_release_buffer(&ms, &mic); | ||
999 | |||
1000 | return (1); | ||
1001 | } | ||
1002 | |||
880 | #endif /* GSSAPI */ | 1003 | #endif /* GSSAPI */ |
881 | 1004 | ||
882 | int | 1005 | int |