xref: /openssh-portable/gss-genr.c (revision 39be3dc2)
1 /* $OpenBSD: gss-genr.c,v 1.28 2021/01/27 10:05:28 djm Exp $ */
2 
3 /*
4  * Copyright (c) 2001-2007 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 <sys/types.h>
32 
33 #include <limits.h>
34 #include <stdarg.h>
35 #include <string.h>
36 #include <signal.h>
37 #include <unistd.h>
38 
39 #include "xmalloc.h"
40 #include "ssherr.h"
41 #include "sshbuf.h"
42 #include "log.h"
43 #include "ssh2.h"
44 
45 #include "ssh-gss.h"
46 
47 /* sshbuf_get for gss_buffer_desc */
48 int
ssh_gssapi_get_buffer_desc(struct sshbuf * b,gss_buffer_desc * g)49 ssh_gssapi_get_buffer_desc(struct sshbuf *b, gss_buffer_desc *g)
50 {
51 	int r;
52 	u_char *p;
53 	size_t len;
54 
55 	if ((r = sshbuf_get_string(b, &p, &len)) != 0)
56 		return r;
57 	g->value = p;
58 	g->length = len;
59 	return 0;
60 }
61 
62 /* Check that the OID in a data stream matches that in the context */
63 int
ssh_gssapi_check_oid(Gssctxt * ctx,void * data,size_t len)64 ssh_gssapi_check_oid(Gssctxt *ctx, void *data, size_t len)
65 {
66 	return (ctx != NULL && ctx->oid != GSS_C_NO_OID &&
67 	    ctx->oid->length == len &&
68 	    memcmp(ctx->oid->elements, data, len) == 0);
69 }
70 
71 /* Set the contexts OID from a data stream */
72 void
ssh_gssapi_set_oid_data(Gssctxt * ctx,void * data,size_t len)73 ssh_gssapi_set_oid_data(Gssctxt *ctx, void *data, size_t len)
74 {
75 	if (ctx->oid != GSS_C_NO_OID) {
76 		free(ctx->oid->elements);
77 		free(ctx->oid);
78 	}
79 	ctx->oid = xcalloc(1, sizeof(gss_OID_desc));
80 	ctx->oid->length = len;
81 	ctx->oid->elements = xmalloc(len);
82 	memcpy(ctx->oid->elements, data, len);
83 }
84 
85 /* Set the contexts OID */
86 void
ssh_gssapi_set_oid(Gssctxt * ctx,gss_OID oid)87 ssh_gssapi_set_oid(Gssctxt *ctx, gss_OID oid)
88 {
89 	ssh_gssapi_set_oid_data(ctx, oid->elements, oid->length);
90 }
91 
92 /* All this effort to report an error ... */
93 void
ssh_gssapi_error(Gssctxt * ctxt)94 ssh_gssapi_error(Gssctxt *ctxt)
95 {
96 	char *s;
97 
98 	s = ssh_gssapi_last_error(ctxt, NULL, NULL);
99 	debug("%s", s);
100 	free(s);
101 }
102 
103 char *
ssh_gssapi_last_error(Gssctxt * ctxt,OM_uint32 * major_status,OM_uint32 * minor_status)104 ssh_gssapi_last_error(Gssctxt *ctxt, OM_uint32 *major_status,
105     OM_uint32 *minor_status)
106 {
107 	OM_uint32 lmin;
108 	gss_buffer_desc msg = GSS_C_EMPTY_BUFFER;
109 	OM_uint32 ctx;
110 	struct sshbuf *b;
111 	char *ret;
112 	int r;
113 
114 	if ((b = sshbuf_new()) == NULL)
115 		fatal_f("sshbuf_new failed");
116 
117 	if (major_status != NULL)
118 		*major_status = ctxt->major;
119 	if (minor_status != NULL)
120 		*minor_status = ctxt->minor;
121 
122 	ctx = 0;
123 	/* The GSSAPI error */
124 	do {
125 		gss_display_status(&lmin, ctxt->major,
126 		    GSS_C_GSS_CODE, ctxt->oid, &ctx, &msg);
127 
128 		if ((r = sshbuf_put(b, msg.value, msg.length)) != 0 ||
129 		    (r = sshbuf_put_u8(b, '\n')) != 0)
130 			fatal_fr(r, "assemble GSS_CODE");
131 
132 		gss_release_buffer(&lmin, &msg);
133 	} while (ctx != 0);
134 
135 	/* The mechanism specific error */
136 	do {
137 		gss_display_status(&lmin, ctxt->minor,
138 		    GSS_C_MECH_CODE, ctxt->oid, &ctx, &msg);
139 
140 		if ((r = sshbuf_put(b, msg.value, msg.length)) != 0 ||
141 		    (r = sshbuf_put_u8(b, '\n')) != 0)
142 			fatal_fr(r, "assemble MECH_CODE");
143 
144 		gss_release_buffer(&lmin, &msg);
145 	} while (ctx != 0);
146 
147 	if ((r = sshbuf_put_u8(b, '\n')) != 0)
148 		fatal_fr(r, "assemble newline");
149 	ret = xstrdup((const char *)sshbuf_ptr(b));
150 	sshbuf_free(b);
151 	return (ret);
152 }
153 
154 /*
155  * Initialise our GSSAPI context. We use this opaque structure to contain all
156  * of the data which both the client and server need to persist across
157  * {accept,init}_sec_context calls, so that when we do it from the userauth
158  * stuff life is a little easier
159  */
160 void
ssh_gssapi_build_ctx(Gssctxt ** ctx)161 ssh_gssapi_build_ctx(Gssctxt **ctx)
162 {
163 	*ctx = xcalloc(1, sizeof (Gssctxt));
164 	(*ctx)->context = GSS_C_NO_CONTEXT;
165 	(*ctx)->name = GSS_C_NO_NAME;
166 	(*ctx)->oid = GSS_C_NO_OID;
167 	(*ctx)->creds = GSS_C_NO_CREDENTIAL;
168 	(*ctx)->client = GSS_C_NO_NAME;
169 	(*ctx)->client_creds = GSS_C_NO_CREDENTIAL;
170 }
171 
172 /* Delete our context, providing it has been built correctly */
173 void
ssh_gssapi_delete_ctx(Gssctxt ** ctx)174 ssh_gssapi_delete_ctx(Gssctxt **ctx)
175 {
176 	OM_uint32 ms;
177 
178 	if ((*ctx) == NULL)
179 		return;
180 	if ((*ctx)->context != GSS_C_NO_CONTEXT)
181 		gss_delete_sec_context(&ms, &(*ctx)->context, GSS_C_NO_BUFFER);
182 	if ((*ctx)->name != GSS_C_NO_NAME)
183 		gss_release_name(&ms, &(*ctx)->name);
184 	if ((*ctx)->oid != GSS_C_NO_OID) {
185 		free((*ctx)->oid->elements);
186 		free((*ctx)->oid);
187 		(*ctx)->oid = GSS_C_NO_OID;
188 	}
189 	if ((*ctx)->creds != GSS_C_NO_CREDENTIAL)
190 		gss_release_cred(&ms, &(*ctx)->creds);
191 	if ((*ctx)->client != GSS_C_NO_NAME)
192 		gss_release_name(&ms, &(*ctx)->client);
193 	if ((*ctx)->client_creds != GSS_C_NO_CREDENTIAL)
194 		gss_release_cred(&ms, &(*ctx)->client_creds);
195 
196 	free(*ctx);
197 	*ctx = NULL;
198 }
199 
200 /*
201  * Wrapper to init_sec_context
202  * Requires that the context contains:
203  *	oid
204  *	server name (from ssh_gssapi_import_name)
205  */
206 OM_uint32
ssh_gssapi_init_ctx(Gssctxt * ctx,int deleg_creds,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)207 ssh_gssapi_init_ctx(Gssctxt *ctx, int deleg_creds, gss_buffer_desc *recv_tok,
208     gss_buffer_desc* send_tok, OM_uint32 *flags)
209 {
210 	int deleg_flag = 0;
211 
212 	if (deleg_creds) {
213 		deleg_flag = GSS_C_DELEG_FLAG;
214 		debug("Delegating credentials");
215 	}
216 
217 	ctx->major = gss_init_sec_context(&ctx->minor,
218 	    GSS_C_NO_CREDENTIAL, &ctx->context, ctx->name, ctx->oid,
219 	    GSS_C_MUTUAL_FLAG | GSS_C_INTEG_FLAG | deleg_flag,
220 	    0, NULL, recv_tok, NULL, send_tok, flags, NULL);
221 
222 	if (GSS_ERROR(ctx->major))
223 		ssh_gssapi_error(ctx);
224 
225 	return (ctx->major);
226 }
227 
228 /* Create a service name for the given host */
229 OM_uint32
ssh_gssapi_import_name(Gssctxt * ctx,const char * host)230 ssh_gssapi_import_name(Gssctxt *ctx, const char *host)
231 {
232 	gss_buffer_desc gssbuf;
233 	char *val;
234 
235 	xasprintf(&val, "host@%s", host);
236 	gssbuf.value = val;
237 	gssbuf.length = strlen(gssbuf.value);
238 
239 	if ((ctx->major = gss_import_name(&ctx->minor,
240 	    &gssbuf, GSS_C_NT_HOSTBASED_SERVICE, &ctx->name)))
241 		ssh_gssapi_error(ctx);
242 
243 	free(gssbuf.value);
244 	return (ctx->major);
245 }
246 
247 OM_uint32
ssh_gssapi_sign(Gssctxt * ctx,gss_buffer_t buffer,gss_buffer_t hash)248 ssh_gssapi_sign(Gssctxt *ctx, gss_buffer_t buffer, gss_buffer_t hash)
249 {
250 	if ((ctx->major = gss_get_mic(&ctx->minor, ctx->context,
251 	    GSS_C_QOP_DEFAULT, buffer, hash)))
252 		ssh_gssapi_error(ctx);
253 
254 	return (ctx->major);
255 }
256 
257 void
ssh_gssapi_buildmic(struct sshbuf * b,const char * user,const char * service,const char * context,const struct sshbuf * session_id)258 ssh_gssapi_buildmic(struct sshbuf *b, const char *user, const char *service,
259     const char *context, const struct sshbuf *session_id)
260 {
261 	int r;
262 
263 	sshbuf_reset(b);
264 	if ((r = sshbuf_put_stringb(b, session_id)) != 0 ||
265 	    (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
266 	    (r = sshbuf_put_cstring(b, user)) != 0 ||
267 	    (r = sshbuf_put_cstring(b, service)) != 0 ||
268 	    (r = sshbuf_put_cstring(b, context)) != 0)
269 		fatal_fr(r, "assemble buildmic");
270 }
271 
272 int
ssh_gssapi_check_mechanism(Gssctxt ** ctx,gss_OID oid,const char * host)273 ssh_gssapi_check_mechanism(Gssctxt **ctx, gss_OID oid, const char *host)
274 {
275 	gss_buffer_desc token = GSS_C_EMPTY_BUFFER;
276 	OM_uint32 major, minor;
277 	gss_OID_desc spnego_oid = {6, (void *)"\x2B\x06\x01\x05\x05\x02"};
278 
279 	/* RFC 4462 says we MUST NOT do SPNEGO */
280 	if (oid->length == spnego_oid.length &&
281 	    (memcmp(oid->elements, spnego_oid.elements, oid->length) == 0))
282 		return 0; /* false */
283 
284 	ssh_gssapi_build_ctx(ctx);
285 	ssh_gssapi_set_oid(*ctx, oid);
286 	major = ssh_gssapi_import_name(*ctx, host);
287 	if (!GSS_ERROR(major)) {
288 		major = ssh_gssapi_init_ctx(*ctx, 0, GSS_C_NO_BUFFER, &token,
289 		    NULL);
290 		gss_release_buffer(&minor, &token);
291 		if ((*ctx)->context != GSS_C_NO_CONTEXT)
292 			gss_delete_sec_context(&minor, &(*ctx)->context,
293 			    GSS_C_NO_BUFFER);
294 	}
295 
296 	if (GSS_ERROR(major))
297 		ssh_gssapi_delete_ctx(ctx);
298 
299 	return (!GSS_ERROR(major));
300 }
301 
302 #endif /* GSSAPI */
303