gss-serv.c

   1 /* $OpenBSD: gss-serv.c,v 1.19 2006/07/22 20:48:23 stevesk Exp $ */
   2
   3 /*
   4  * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "includes.h"
  28
  29 #ifdef GSSAPI
  30
  31 #include <string.h>
  32 #include <unistd.h>
  33
  34 #include "bufaux.h"
  35 #include "auth.h"
  36 #include "log.h"
  37 #include "channels.h"
  38 #include "session.h"
  39 #include "xmalloc.h"
  40 #include "misc.h"
  41
  42 #include "ssh-gss.h"
  43
  44 static ssh_gssapi_client gssapi_client =
  45     { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
  46     GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL}};
  47
  48 ssh_gssapi_mech gssapi_null_mech =
  49     { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
  50
  51 #ifdef KRB5
  52 extern ssh_gssapi_mech gssapi_kerberos_mech;
  53 #endif
  54
  55 ssh_gssapi_mech* supported_mechs[]= {
  56 #ifdef KRB5
  57         &gssapi_kerberos_mech,
  58 #endif
  59         &gssapi_null_mech,
  60 };
  61
  62 /* Unprivileged */
  63 void
  64 ssh_gssapi_supported_oids(gss_OID_set *oidset)
  65 {
  66         int i = 0;
  67         OM_uint32 min_status;
  68         int present;
  69         gss_OID_set supported;
  70
  71         gss_create_empty_oid_set(&min_status, oidset);
  72         gss_indicate_mechs(&min_status, &supported);
  73
  74         while (supported_mechs[i]->name != NULL) {
  75                 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
  76                     &supported_mechs[i]->oid, supported, &present)))
  77                         present = 0;
  78                 if (present)
  79                         gss_add_oid_set_member(&min_status,
  80                             &supported_mechs[i]->oid, oidset);
  81                 i++;
  82         }
  83
  84         gss_release_oid_set(&min_status, &supported);
  85 }
  86
  87
  88 /* Wrapper around accept_sec_context
  89  * Requires that the context contains:
  90  *    oid
  91  *    credentials       (from ssh_gssapi_acquire_cred)
  92  */
  93 /* Privileged */
  94 OM_uint32
  95 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
  96     gss_buffer_desc *send_tok, OM_uint32 *flags)
  97 {
  98         OM_uint32 status;
  99         gss_OID mech;
 100
 101         ctx->major = gss_accept_sec_context(&ctx->minor,
 102             &ctx->context, ctx->creds, recv_tok,
 103             GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
 104             send_tok, flags, NULL, &ctx->client_creds);
 105
 106         if (GSS_ERROR(ctx->major))
 107                 ssh_gssapi_error(ctx);
 108
 109         if (ctx->client_creds)
 110                 debug("Received some client credentials");
 111         else
 112                 debug("Got no client credentials");
 113
 114         status = ctx->major;
 115
 116         /* Now, if we're complete and we have the right flags, then
 117          * we flag the user as also having been authenticated
 118          */
 119
 120         if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
 121             (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
 122                 if (ssh_gssapi_getclient(ctx, &gssapi_client))
 123                         fatal("Couldn't convert client name");
 124         }
 125
 126         return (status);
 127 }
 128
 129 /*
 130  * This parses an exported name, extracting the mechanism specific portion
 131  * to use for ACL checking. It verifies that the name belongs the mechanism
 132  * originally selected.
 133  */
 134 static OM_uint32
 135 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
 136 {
 137         u_char *tok;
 138         OM_uint32 offset;
 139         OM_uint32 oidl;
 140
 141         tok = ename->value;
 142
 143         /*
 144          * Check that ename is long enough for all of the fixed length
 145          * header, and that the initial ID bytes are correct
 146          */
 147
 148         if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
 149                 return GSS_S_FAILURE;
 150
 151         /*
 152          * Extract the OID, and check it. Here GSSAPI breaks with tradition
 153          * and does use the OID type and length bytes. To confuse things
 154          * there are two lengths - the first including these, and the
 155          * second without.
 156          */
 157
 158         oidl = get_u16(tok+2); /* length including next two bytes */
 159         oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
 160
 161         /*
 162          * Check the BER encoding for correct type and length, that the
 163          * string is long enough and that the OID matches that in our context
 164          */
 165         if (tok[4] != 0x06 || tok[5] != oidl ||
 166             ename->length < oidl+6 ||
 167             !ssh_gssapi_check_oid(ctx, tok+6, oidl))
 168                 return GSS_S_FAILURE;
 169
 170         offset = oidl+6;
 171
 172         if (ename->length < offset+4)
 173                 return GSS_S_FAILURE;
 174
 175         name->length = get_u32(tok+offset);
 176         offset += 4;
 177
 178         if (ename->length < offset+name->length)
 179                 return GSS_S_FAILURE;
 180
 181         name->value = xmalloc(name->length+1);
 182         memcpy(name->value, tok+offset, name->length);
 183         ((char *)name->value)[name->length] = 0;
 184
 185         return GSS_S_COMPLETE;
 186 }
 187
 188 /* Extract the client details from a given context. This can only reliably
 189  * be called once for a context */
 190
 191 /* Privileged (called from accept_secure_ctx) */
 192 OM_uint32
 193 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
 194 {
 195         int i = 0;
 196
 197         gss_buffer_desc ename;
 198
 199         client->mech = NULL;
 200
 201         while (supported_mechs[i]->name != NULL) {
 202                 if (supported_mechs[i]->oid.length == ctx->oid->length &&
 203                     (memcmp(supported_mechs[i]->oid.elements,
 204                     ctx->oid->elements, ctx->oid->length) == 0))
 205                         client->mech = supported_mechs[i];
 206                 i++;
 207         }
 208
 209         if (client->mech == NULL)
 210                 return GSS_S_FAILURE;
 211
 212         if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
 213             &client->displayname, NULL))) {
 214                 ssh_gssapi_error(ctx);
 215                 return (ctx->major);
 216         }
 217
 218         if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
 219             &ename))) {
 220                 ssh_gssapi_error(ctx);
 221                 return (ctx->major);
 222         }
 223
 224         if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
 225             &client->exportedname))) {
 226                 return (ctx->major);
 227         }
 228
 229         /* We can't copy this structure, so we just move the pointer to it */
 230         client->creds = ctx->client_creds;
 231         ctx->client_creds = GSS_C_NO_CREDENTIAL;
 232         return (ctx->major);
 233 }
 234
 235 /* As user - called on fatal/exit */
 236 void
 237 ssh_gssapi_cleanup_creds(void)
 238 {
 239         if (gssapi_client.store.filename != NULL) {
 240                 /* Unlink probably isn't sufficient */
 241                 debug("removing gssapi cred file\"%s\"",
 242                     gssapi_client.store.filename);
 243                 unlink(gssapi_client.store.filename);
 244         }
 245 }
 246
 247 /* As user */
 248 void
 249 ssh_gssapi_storecreds(void)
 250 {
 251         if (gssapi_client.mech && gssapi_client.mech->storecreds) {
 252                 (*gssapi_client.mech->storecreds)(&gssapi_client);
 253         } else
 254                 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
 255 }
 256
 257 /* This allows GSSAPI methods to do things to the childs environment based
 258  * on the passed authentication process and credentials.
 259  */
 260 /* As user */
 261 void
 262 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
 263 {
 264
 265         if (gssapi_client.store.envvar != NULL &&
 266             gssapi_client.store.envval != NULL) {
 267                 debug("Setting %s to %s", gssapi_client.store.envvar,
 268                     gssapi_client.store.envval);
 269                 child_set_env(envp, envsizep, gssapi_client.store.envvar,
 270                     gssapi_client.store.envval);
 271         }
 272 }
 273
 274 /* Privileged */
 275 int
 276 ssh_gssapi_userok(char *user)
 277 {
 278         OM_uint32 lmin;
 279
 280         if (gssapi_client.exportedname.length == 0 ||
 281             gssapi_client.exportedname.value == NULL) {
 282                 debug("No suitable client data");
 283                 return 0;
 284         }
 285         if (gssapi_client.mech && gssapi_client.mech->userok)
 286                 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
 287                         return 1;
 288                 else {
 289                         /* Destroy delegated credentials if userok fails */
 290                         gss_release_buffer(&lmin, &gssapi_client.displayname);
 291                         gss_release_buffer(&lmin, &gssapi_client.exportedname);
 292                         gss_release_cred(&lmin, &gssapi_client.creds);
 293                         memset(&gssapi_client, 0, sizeof(ssh_gssapi_client));
 294                         return 0;
 295                 }
 296         else
 297                 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
 298         return (0);
 299 }
 300
 301 /* Privileged */
 302 OM_uint32
 303 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
 304 {
 305         ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
 306             gssbuf, gssmic, NULL);
 307
 308         return (ctx->major);
 309 }
 310
 311 #endif