xref: /openssh-portable/ssh-sk-helper.c (revision 59d01f1d)
1 /* $OpenBSD: ssh-sk-helper.c,v 1.9 2020/01/25 23:13:09 djm Exp $ */
2 /*
3  * Copyright (c) 2019 Google LLC
4  *
5  * Permission to use, copy, modify, and distribute this software for any
6  * purpose with or without fee is hereby granted, provided that the above
7  * copyright notice and this permission notice appear in all copies.
8  *
9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16  */
17 
18 /*
19  * This is a tiny program used to isolate the address space used for
20  * security key middleware signing operations from ssh-agent. It is similar
21  * to ssh-pkcs11-helper.c but considerably simpler as the operations for
22  * security keys are stateless.
23  *
24  * Please crank SSH_SK_HELPER_VERSION in sshkey.h for any incompatible
25  * protocol changes.
26  */
27 
28 #include "includes.h"
29 
30 #include <limits.h>
31 #include <stdarg.h>
32 #include <stdio.h>
33 #include <stdlib.h>
34 #include <string.h>
35 #include <unistd.h>
36 #include <errno.h>
37 
38 #include "xmalloc.h"
39 #include "log.h"
40 #include "sshkey.h"
41 #include "authfd.h"
42 #include "misc.h"
43 #include "sshbuf.h"
44 #include "msg.h"
45 #include "uidswap.h"
46 #include "sshkey.h"
47 #include "ssherr.h"
48 #include "ssh-sk.h"
49 
50 #ifdef ENABLE_SK
51 extern char *__progname;
52 
53 static struct sshbuf *reply_error(int r, char *fmt, ...)
54     __attribute__((__format__ (printf, 2, 3)));
55 
56 static struct sshbuf *
reply_error(int r,char * fmt,...)57 reply_error(int r, char *fmt, ...)
58 {
59 	char *msg;
60 	va_list ap;
61 	struct sshbuf *resp;
62 
63 	va_start(ap, fmt);
64 	xvasprintf(&msg, fmt, ap);
65 	va_end(ap);
66 	debug("%s: %s", __progname, msg);
67 	free(msg);
68 
69 	if (r >= 0)
70 		fatal("%s: invalid error code %d", __func__, r);
71 
72 	if ((resp = sshbuf_new()) == NULL)
73 		fatal("%s: sshbuf_new failed", __progname);
74 	if (sshbuf_put_u32(resp, SSH_SK_HELPER_ERROR) != 0 ||
75 	    sshbuf_put_u32(resp, (u_int)-r) != 0)
76 		fatal("%s: buffer error", __progname);
77 	return resp;
78 }
79 
80 /* If the specified string is zero length, then free it and replace with NULL */
81 static void
null_empty(char ** s)82 null_empty(char **s)
83 {
84 	if (s == NULL || *s == NULL || **s != '\0')
85 		return;
86 
87 	free(*s);
88 	*s = NULL;
89 }
90 
91 static struct sshbuf *
process_sign(struct sshbuf * req)92 process_sign(struct sshbuf *req)
93 {
94 	int r = SSH_ERR_INTERNAL_ERROR;
95 	struct sshbuf *resp, *kbuf;
96 	struct sshkey *key;
97 	uint32_t compat;
98 	const u_char *message;
99 	u_char *sig;
100 	size_t msglen, siglen;
101 	char *provider, *pin;
102 
103 	if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
104 	    (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
105 	    (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
106 	    (r = sshbuf_get_cstring(req, NULL, NULL)) != 0 || /* alg */
107 	    (r = sshbuf_get_u32(req, &compat)) != 0 ||
108 	    (r = sshbuf_get_cstring(req, &pin, NULL)) != 0)
109 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
110 	if (sshbuf_len(req) != 0)
111 		fatal("%s: trailing data in request", __progname);
112 
113 	if ((r = sshkey_private_deserialize(kbuf, &key)) != 0)
114 		fatal("Unable to parse private key: %s", ssh_err(r));
115 	if (!sshkey_is_sk(key))
116 		fatal("Unsupported key type %s", sshkey_ssh_name(key));
117 
118 	debug("%s: ready to sign with key %s, provider %s: "
119 	    "msg len %zu, compat 0x%lx", __progname, sshkey_type(key),
120 	    provider, msglen, (u_long)compat);
121 
122 	null_empty(&pin);
123 
124 	if ((r = sshsk_sign(provider, key, &sig, &siglen,
125 	    message, msglen, compat, pin)) != 0) {
126 		resp = reply_error(r, "Signing failed: %s", ssh_err(r));
127 		goto out;
128 	}
129 
130 	if ((resp = sshbuf_new()) == NULL)
131 		fatal("%s: sshbuf_new failed", __progname);
132 
133 	if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_SIGN)) != 0 ||
134 	    (r = sshbuf_put_string(resp, sig, siglen)) != 0)
135 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
136  out:
137 	sshbuf_free(kbuf);
138 	free(provider);
139 	if (pin != NULL)
140 		freezero(pin, strlen(pin));
141 	return resp;
142 }
143 
144 static struct sshbuf *
process_enroll(struct sshbuf * req)145 process_enroll(struct sshbuf *req)
146 {
147 	int r;
148 	u_int type;
149 	char *provider, *application, *pin, *device, *userid;
150 	uint8_t flags;
151 	struct sshbuf *challenge, *attest, *kbuf, *resp;
152 	struct sshkey *key;
153 
154 	if ((attest = sshbuf_new()) == NULL ||
155 	    (kbuf = sshbuf_new()) == NULL)
156 		fatal("%s: sshbuf_new failed", __progname);
157 
158 	if ((r = sshbuf_get_u32(req, &type)) != 0 ||
159 	    (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
160 	    (r = sshbuf_get_cstring(req, &device, NULL)) != 0 ||
161 	    (r = sshbuf_get_cstring(req, &application, NULL)) != 0 ||
162 	    (r = sshbuf_get_cstring(req, &userid, NULL)) != 0 ||
163 	    (r = sshbuf_get_u8(req, &flags)) != 0 ||
164 	    (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 ||
165 	    (r = sshbuf_froms(req, &challenge)) != 0)
166 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
167 	if (sshbuf_len(req) != 0)
168 		fatal("%s: trailing data in request", __progname);
169 
170 	if (type > INT_MAX)
171 		fatal("%s: bad type %u", __progname, type);
172 	if (sshbuf_len(challenge) == 0) {
173 		sshbuf_free(challenge);
174 		challenge = NULL;
175 	}
176 	null_empty(&device);
177 	null_empty(&userid);
178 	null_empty(&pin);
179 
180 	if ((r = sshsk_enroll((int)type, provider, device, application, userid,
181 	    flags, pin, challenge, &key, attest)) != 0) {
182 		resp = reply_error(r, "Enrollment failed: %s", ssh_err(r));
183 		goto out;
184 	}
185 
186 	if ((resp = sshbuf_new()) == NULL)
187 		fatal("%s: sshbuf_new failed", __progname);
188 	if ((r = sshkey_private_serialize(key, kbuf)) != 0)
189 		fatal("%s: serialize private key: %s", __progname, ssh_err(r));
190 	if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_ENROLL)) != 0 ||
191 	    (r = sshbuf_put_stringb(resp, kbuf)) != 0 ||
192 	    (r = sshbuf_put_stringb(resp, attest)) != 0)
193 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
194 
195  out:
196 	sshkey_free(key);
197 	sshbuf_free(kbuf);
198 	sshbuf_free(attest);
199 	sshbuf_free(challenge);
200 	free(provider);
201 	free(application);
202 	if (pin != NULL)
203 		freezero(pin, strlen(pin));
204 
205 	return resp;
206 }
207 
208 static struct sshbuf *
process_load_resident(struct sshbuf * req)209 process_load_resident(struct sshbuf *req)
210 {
211 	int r;
212 	char *provider, *pin, *device;
213 	struct sshbuf *kbuf, *resp;
214 	struct sshkey **keys = NULL;
215 	size_t nkeys = 0, i;
216 
217 	if ((kbuf = sshbuf_new()) == NULL)
218 		fatal("%s: sshbuf_new failed", __progname);
219 
220 	if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
221 	    (r = sshbuf_get_cstring(req, &device, NULL)) != 0 ||
222 	    (r = sshbuf_get_cstring(req, &pin, NULL)) != 0)
223 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
224 	if (sshbuf_len(req) != 0)
225 		fatal("%s: trailing data in request", __progname);
226 
227 	null_empty(&device);
228 	null_empty(&pin);
229 
230 	if ((r = sshsk_load_resident(provider, device, pin,
231 	    &keys, &nkeys)) != 0) {
232 		resp = reply_error(r, " sshsk_load_resident failed: %s",
233 		    ssh_err(r));
234 		goto out;
235 	}
236 
237 	if ((resp = sshbuf_new()) == NULL)
238 		fatal("%s: sshbuf_new failed", __progname);
239 
240 	if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
241 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
242 
243 	for (i = 0; i < nkeys; i++) {
244 		debug("%s: key %zu %s %s", __func__, i,
245 		    sshkey_type(keys[i]), keys[i]->sk_application);
246 		sshbuf_reset(kbuf);
247 		if ((r = sshkey_private_serialize(keys[i], kbuf)) != 0)
248 			fatal("%s: serialize private key: %s",
249 			    __progname, ssh_err(r));
250 		if ((r = sshbuf_put_stringb(resp, kbuf)) != 0 ||
251 		    (r = sshbuf_put_cstring(resp, "")) != 0) /* comment */
252 			fatal("%s: buffer error: %s", __progname, ssh_err(r));
253 	}
254 
255  out:
256 	for (i = 0; i < nkeys; i++)
257 		sshkey_free(keys[i]);
258 	free(keys);
259 	sshbuf_free(kbuf);
260 	free(provider);
261 	if (pin != NULL)
262 		freezero(pin, strlen(pin));
263 	return resp;
264 }
265 
266 int
main(int argc,char ** argv)267 main(int argc, char **argv)
268 {
269 	SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
270 	LogLevel log_level = SYSLOG_LEVEL_ERROR;
271 	struct sshbuf *req, *resp;
272 	int in, out, ch, r, vflag = 0;
273 	u_int rtype, ll = 0;
274 	uint8_t version, log_stderr = 0;
275 
276 	sanitise_stdfd();
277 	log_init(__progname, log_level, log_facility, log_stderr);
278 
279 	while ((ch = getopt(argc, argv, "v")) != -1) {
280 		switch (ch) {
281 		case 'v':
282 			vflag = 1;
283 			if (log_level == SYSLOG_LEVEL_ERROR)
284 				log_level = SYSLOG_LEVEL_DEBUG1;
285 			else if (log_level < SYSLOG_LEVEL_DEBUG3)
286 				log_level++;
287 			break;
288 		default:
289 			fprintf(stderr, "usage: %s [-v]\n", __progname);
290 			exit(1);
291 		}
292 	}
293 	log_init(__progname, log_level, log_facility, vflag);
294 
295 	/*
296 	 * Rearrange our file descriptors a little; we don't trust the
297 	 * providers not to fiddle with stdin/out.
298 	 */
299 	closefrom(STDERR_FILENO + 1);
300 	if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1)
301 		fatal("%s: dup: %s", __progname, strerror(errno));
302 	close(STDIN_FILENO);
303 	close(STDOUT_FILENO);
304 	sanitise_stdfd(); /* resets to /dev/null */
305 
306 	if ((req = sshbuf_new()) == NULL)
307 		fatal("%s: sshbuf_new failed", __progname);
308 	if (ssh_msg_recv(in, req) < 0)
309 		fatal("ssh_msg_recv failed");
310 	close(in);
311 	debug("%s: received message len %zu", __progname, sshbuf_len(req));
312 
313 	if ((r = sshbuf_get_u8(req, &version)) != 0)
314 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
315 	if (version != SSH_SK_HELPER_VERSION) {
316 		fatal("unsupported version: received %d, expected %d",
317 		    version, SSH_SK_HELPER_VERSION);
318 	}
319 
320 	if ((r = sshbuf_get_u32(req, &rtype)) != 0 ||
321 	    (r = sshbuf_get_u8(req, &log_stderr)) != 0 ||
322 	    (r = sshbuf_get_u32(req, &ll)) != 0)
323 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
324 
325 	if (!vflag && log_level_name((LogLevel)ll) != NULL)
326 		log_init(__progname, (LogLevel)ll, log_facility, log_stderr);
327 
328 	switch (rtype) {
329 	case SSH_SK_HELPER_SIGN:
330 		resp = process_sign(req);
331 		break;
332 	case SSH_SK_HELPER_ENROLL:
333 		resp = process_enroll(req);
334 		break;
335 	case SSH_SK_HELPER_LOAD_RESIDENT:
336 		resp = process_load_resident(req);
337 		break;
338 	default:
339 		fatal("%s: unsupported request type %u", __progname, rtype);
340 	}
341 	sshbuf_free(req);
342 	debug("%s: reply len %zu", __progname, sshbuf_len(resp));
343 
344 	if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1)
345 		fatal("ssh_msg_send failed");
346 	sshbuf_free(resp);
347 	close(out);
348 
349 	return (0);
350 }
351 #else /* ENABLE_SK */
352 #include <stdio.h>
353 
354 int
main(int argc,char ** argv)355 main(int argc, char **argv)
356 {
357 	fprintf(stderr, "ssh-sk-helper: disabled at compile time\n");
358 	return -1;
359 }
360 #endif /* ENABLE_SK */
361