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ssh-sk-client.c revision 1.1.1.4 
      1 /* $OpenBSD: ssh-sk-client.c,v 1.12 2022/01/14 03:34:00 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 #include <sys/types.h>
     19 #include <sys/socket.h>
     20 #include <sys/wait.h>
     21 
     22 #include <fcntl.h>
     23 #include <limits.h>
     24 #include <errno.h>
     25 #include <signal.h>
     26 #include <stdarg.h>
     27 #include <stdio.h>
     28 #include <stdlib.h>
     29 #include <string.h>
     30 #include <unistd.h>
     31 
     32 #include "log.h"
     33 #include "ssherr.h"
     34 #include "sshbuf.h"
     35 #include "sshkey.h"
     36 #include "msg.h"
     37 #include "digest.h"
     38 #include "pathnames.h"
     39 #include "ssh-sk.h"
     40 #include "misc.h"
     41 
     42 /* #define DEBUG_SK 1 */
     43 
     44 static int
     45 start_helper(int *fdp, pid_t *pidp, void (**osigchldp)(int))
     46 {
     47 	void (*osigchld)(int);
     48 	int oerrno, pair[2];
     49 	pid_t pid;
     50 	char *helper, *verbosity = NULL;
     51 
     52 	*fdp = -1;
     53 	*pidp = 0;
     54 	*osigchldp = SIG_DFL;
     55 
     56 	helper = getenv("SSH_SK_HELPER");
     57 	if (helper == NULL || strlen(helper) == 0)
     58 		helper = _PATH_SSH_SK_HELPER;
     59 	if (access(helper, X_OK) != 0) {
     60 		oerrno = errno;
     61 		error_f("helper \"%s\" unusable: %s", helper, strerror(errno));
     62 		errno = oerrno;
     63 		return SSH_ERR_SYSTEM_ERROR;
     64 	}
     65 #ifdef DEBUG_SK
     66 	verbosity = "-vvv";
     67 #endif
     68 
     69 	/* Start helper */
     70 	if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
     71 		error("socketpair: %s", strerror(errno));
     72 		return SSH_ERR_SYSTEM_ERROR;
     73 	}
     74 	osigchld = ssh_signal(SIGCHLD, SIG_DFL);
     75 	if ((pid = fork()) == -1) {
     76 		oerrno = errno;
     77 		error("fork: %s", strerror(errno));
     78 		close(pair[0]);
     79 		close(pair[1]);
     80 		ssh_signal(SIGCHLD, osigchld);
     81 		errno = oerrno;
     82 		return SSH_ERR_SYSTEM_ERROR;
     83 	}
     84 	if (pid == 0) {
     85 		if ((dup2(pair[1], STDIN_FILENO) == -1) ||
     86 		    (dup2(pair[1], STDOUT_FILENO) == -1)) {
     87 			error_f("dup2: %s", strerror(errno));
     88 			_exit(1);
     89 		}
     90 		close(pair[0]);
     91 		close(pair[1]);
     92 		closefrom(STDERR_FILENO + 1);
     93 		debug_f("starting %s %s", helper,
     94 		    verbosity == NULL ? "" : verbosity);
     95 		execlp(helper, helper, verbosity, (char *)NULL);
     96 		error_f("execlp: %s", strerror(errno));
     97 		_exit(1);
     98 	}
     99 	close(pair[1]);
    100 
    101 	/* success */
    102 	debug3_f("started pid=%ld", (long)pid);
    103 	*fdp = pair[0];
    104 	*pidp = pid;
    105 	*osigchldp = osigchld;
    106 	return 0;
    107 }
    108 
    109 static int
    110 reap_helper(pid_t pid)
    111 {
    112 	int status, oerrno;
    113 
    114 	debug3_f("pid=%ld", (long)pid);
    115 
    116 	errno = 0;
    117 	while (waitpid(pid, &status, 0) == -1) {
    118 		if (errno == EINTR) {
    119 			errno = 0;
    120 			continue;
    121 		}
    122 		oerrno = errno;
    123 		error_f("waitpid: %s", strerror(errno));
    124 		errno = oerrno;
    125 		return SSH_ERR_SYSTEM_ERROR;
    126 	}
    127 	if (!WIFEXITED(status)) {
    128 		error_f("helper exited abnormally");
    129 		return SSH_ERR_AGENT_FAILURE;
    130 	} else if (WEXITSTATUS(status) != 0) {
    131 		error_f("helper exited with non-zero exit status");
    132 		return SSH_ERR_AGENT_FAILURE;
    133 	}
    134 	return 0;
    135 }
    136 
    137 static int
    138 client_converse(struct sshbuf *msg, struct sshbuf **respp, u_int type)
    139 {
    140 	int oerrno, fd, r2, ll, r = SSH_ERR_INTERNAL_ERROR;
    141 	u_int rtype, rerr;
    142 	pid_t pid;
    143 	u_char version;
    144 	void (*osigchld)(int);
    145 	struct sshbuf *req = NULL, *resp = NULL;
    146 	*respp = NULL;
    147 
    148 	if ((r = start_helper(&fd, &pid, &osigchld)) != 0)
    149 		return r;
    150 
    151 	if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL) {
    152 		r = SSH_ERR_ALLOC_FAIL;
    153 		goto out;
    154 	}
    155 	/* Request preamble: type, log_on_stderr, log_level */
    156 	ll = log_level_get();
    157 	if ((r = sshbuf_put_u32(req, type)) != 0 ||
    158 	    (r = sshbuf_put_u8(req, log_is_on_stderr() != 0)) != 0 ||
    159 	    (r = sshbuf_put_u32(req, ll < 0 ? 0 : ll)) != 0 ||
    160 	    (r = sshbuf_putb(req, msg)) != 0) {
    161 		error_fr(r, "compose");
    162 		goto out;
    163 	}
    164 	if ((r = ssh_msg_send(fd, SSH_SK_HELPER_VERSION, req)) != 0) {
    165 		error_fr(r, "send");
    166 		goto out;
    167 	}
    168 	if ((r = ssh_msg_recv(fd, resp)) != 0) {
    169 		error_fr(r, "receive");
    170 		goto out;
    171 	}
    172 	if ((r = sshbuf_get_u8(resp, &version)) != 0) {
    173 		error_fr(r, "parse version");
    174 		goto out;
    175 	}
    176 	if (version != SSH_SK_HELPER_VERSION) {
    177 		error_f("unsupported version: got %u, expected %u",
    178 		    version, SSH_SK_HELPER_VERSION);
    179 		r = SSH_ERR_INVALID_FORMAT;
    180 		goto out;
    181 	}
    182 	if ((r = sshbuf_get_u32(resp, &rtype)) != 0) {
    183 		error_fr(r, "parse message type");
    184 		goto out;
    185 	}
    186 	if (rtype == SSH_SK_HELPER_ERROR) {
    187 		if ((r = sshbuf_get_u32(resp, &rerr)) != 0) {
    188 			error_fr(r, "parse");
    189 			goto out;
    190 		}
    191 		debug_f("helper returned error -%u", rerr);
    192 		/* OpenSSH error values are negative; encoded as -err on wire */
    193 		if (rerr == 0 || rerr >= INT_MAX)
    194 			r = SSH_ERR_INTERNAL_ERROR;
    195 		else
    196 			r = -(int)rerr;
    197 		goto out;
    198 	} else if (rtype != type) {
    199 		error_f("helper returned incorrect message type %u, "
    200 		    "expecting %u", rtype, type);
    201 		r = SSH_ERR_INTERNAL_ERROR;
    202 		goto out;
    203 	}
    204 	/* success */
    205 	r = 0;
    206  out:
    207 	oerrno = errno;
    208 	close(fd);
    209 	if ((r2 = reap_helper(pid)) != 0) {
    210 		if (r == 0) {
    211 			r = r2;
    212 			oerrno = errno;
    213 		}
    214 	}
    215 	if (r == 0) {
    216 		*respp = resp;
    217 		resp = NULL;
    218 	}
    219 	sshbuf_free(req);
    220 	sshbuf_free(resp);
    221 	ssh_signal(SIGCHLD, osigchld);
    222 	errno = oerrno;
    223 	return r;
    224 
    225 }
    226 
    227 int
    228 sshsk_sign(const char *provider, struct sshkey *key,
    229     u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
    230     u_int compat, const char *pin)
    231 {
    232 	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
    233 	struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
    234 
    235 	*sigp = NULL;
    236 	*lenp = 0;
    237 
    238 	if ((kbuf = sshbuf_new()) == NULL ||
    239 	    (req = sshbuf_new()) == NULL) {
    240 		r = SSH_ERR_ALLOC_FAIL;
    241 		goto out;
    242 	}
    243 
    244 	if ((r = sshkey_private_serialize(key, kbuf)) != 0) {
    245 		error_fr(r, "encode key");
    246 		goto out;
    247 	}
    248 	if ((r = sshbuf_put_stringb(req, kbuf)) != 0 ||
    249 	    (r = sshbuf_put_cstring(req, provider)) != 0 ||
    250 	    (r = sshbuf_put_string(req, data, datalen)) != 0 ||
    251 	    (r = sshbuf_put_cstring(req, NULL)) != 0 || /* alg */
    252 	    (r = sshbuf_put_u32(req, compat)) != 0 ||
    253 	    (r = sshbuf_put_cstring(req, pin)) != 0) {
    254 		error_fr(r, "compose");
    255 		goto out;
    256 	}
    257 
    258 	if ((r = client_converse(req, &resp, SSH_SK_HELPER_SIGN)) != 0)
    259 		goto out;
    260 
    261 	if ((r = sshbuf_get_string(resp, sigp, lenp)) != 0) {
    262 		error_fr(r, "parse signature");
    263 		r = SSH_ERR_INVALID_FORMAT;
    264 		goto out;
    265 	}
    266 	if (sshbuf_len(resp) != 0) {
    267 		error_f("trailing data in response");
    268 		r = SSH_ERR_INVALID_FORMAT;
    269 		goto out;
    270 	}
    271 	/* success */
    272 	r = 0;
    273  out:
    274 	oerrno = errno;
    275 	if (r != 0) {
    276 		freezero(*sigp, *lenp);
    277 		*sigp = NULL;
    278 		*lenp = 0;
    279 	}
    280 	sshbuf_free(kbuf);
    281 	sshbuf_free(req);
    282 	sshbuf_free(resp);
    283 	errno = oerrno;
    284 	return r;
    285 }
    286 
    287 int
    288 sshsk_enroll(int type, const char *provider_path, const char *device,
    289     const char *application, const char *userid, uint8_t flags,
    290     const char *pin, struct sshbuf *challenge_buf,
    291     struct sshkey **keyp, struct sshbuf *attest)
    292 {
    293 	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
    294 	struct sshbuf *kbuf = NULL, *abuf = NULL, *req = NULL, *resp = NULL;
    295 	struct sshkey *key = NULL;
    296 
    297 	*keyp = NULL;
    298 	if (attest != NULL)
    299 		sshbuf_reset(attest);
    300 
    301 	if (type < 0)
    302 		return SSH_ERR_INVALID_ARGUMENT;
    303 
    304 	if ((abuf = sshbuf_new()) == NULL ||
    305 	    (kbuf = sshbuf_new()) == NULL ||
    306 	    (req = sshbuf_new()) == NULL) {
    307 		r = SSH_ERR_ALLOC_FAIL;
    308 		goto out;
    309 	}
    310 
    311 	if ((r = sshbuf_put_u32(req, (u_int)type)) != 0 ||
    312 	    (r = sshbuf_put_cstring(req, provider_path)) != 0 ||
    313 	    (r = sshbuf_put_cstring(req, device)) != 0 ||
    314 	    (r = sshbuf_put_cstring(req, application)) != 0 ||
    315 	    (r = sshbuf_put_cstring(req, userid)) != 0 ||
    316 	    (r = sshbuf_put_u8(req, flags)) != 0 ||
    317 	    (r = sshbuf_put_cstring(req, pin)) != 0 ||
    318 	    (r = sshbuf_put_stringb(req, challenge_buf)) != 0) {
    319 		error_fr(r, "compose");
    320 		goto out;
    321 	}
    322 
    323 	if ((r = client_converse(req, &resp, SSH_SK_HELPER_ENROLL)) != 0)
    324 		goto out;
    325 
    326 	if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
    327 	    (r = sshbuf_get_stringb(resp, abuf)) != 0) {
    328 		error_fr(r, "parse");
    329 		r = SSH_ERR_INVALID_FORMAT;
    330 		goto out;
    331 	}
    332 	if (sshbuf_len(resp) != 0) {
    333 		error_f("trailing data in response");
    334 		r = SSH_ERR_INVALID_FORMAT;
    335 		goto out;
    336 	}
    337 	if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
    338 		error_fr(r, "encode");
    339 		goto out;
    340 	}
    341 	if (attest != NULL && (r = sshbuf_putb(attest, abuf)) != 0) {
    342 		error_fr(r, "encode attestation information");
    343 		goto out;
    344 	}
    345 
    346 	/* success */
    347 	r = 0;
    348 	*keyp = key;
    349 	key = NULL;
    350  out:
    351 	oerrno = errno;
    352 	sshkey_free(key);
    353 	sshbuf_free(kbuf);
    354 	sshbuf_free(abuf);
    355 	sshbuf_free(req);
    356 	sshbuf_free(resp);
    357 	errno = oerrno;
    358 	return r;
    359 }
    360 
    361 static void
    362 sshsk_free_resident_key(struct sshsk_resident_key *srk)
    363 {
    364 	if (srk == NULL)
    365 		return;
    366 	sshkey_free(srk->key);
    367 	freezero(srk->user_id, srk->user_id_len);
    368 	free(srk);
    369 }
    370 
    371 
    372 void
    373 sshsk_free_resident_keys(struct sshsk_resident_key **srks, size_t nsrks)
    374 {
    375 	size_t i;
    376 
    377 	if (srks == NULL || nsrks == 0)
    378 		return;
    379 
    380 	for (i = 0; i < nsrks; i++)
    381 		sshsk_free_resident_key(srks[i]);
    382 	free(srks);
    383 }
    384 
    385 int
    386 sshsk_load_resident(const char *provider_path, const char *device,
    387     const char *pin, u_int flags, struct sshsk_resident_key ***srksp,
    388     size_t *nsrksp)
    389 {
    390 	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
    391 	struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
    392 	struct sshkey *key = NULL;
    393 	struct sshsk_resident_key *srk = NULL, **srks = NULL, **tmp;
    394 	u_char *userid = NULL;
    395 	size_t userid_len = 0, nsrks = 0;
    396 
    397 	*srksp = NULL;
    398 	*nsrksp = 0;
    399 
    400 	if ((kbuf = sshbuf_new()) == NULL ||
    401 	    (req = sshbuf_new()) == NULL) {
    402 		r = SSH_ERR_ALLOC_FAIL;
    403 		goto out;
    404 	}
    405 
    406 	if ((r = sshbuf_put_cstring(req, provider_path)) != 0 ||
    407 	    (r = sshbuf_put_cstring(req, device)) != 0 ||
    408 	    (r = sshbuf_put_cstring(req, pin)) != 0 ||
    409 	    (r = sshbuf_put_u32(req, flags)) != 0) {
    410 		error_fr(r, "compose");
    411 		goto out;
    412 	}
    413 
    414 	if ((r = client_converse(req, &resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
    415 		goto out;
    416 
    417 	while (sshbuf_len(resp) != 0) {
    418 		/* key, comment, user_id */
    419 		if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
    420 		    (r = sshbuf_get_cstring(resp, NULL, NULL)) != 0 ||
    421 		    (r = sshbuf_get_string(resp, &userid, &userid_len)) != 0) {
    422 			error_fr(r, "parse");
    423 			r = SSH_ERR_INVALID_FORMAT;
    424 			goto out;
    425 		}
    426 		if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
    427 			error_fr(r, "decode key");
    428 			goto out;
    429 		}
    430 		if ((srk = calloc(1, sizeof(*srk))) == NULL) {
    431 			error_f("calloc failed");
    432 			goto out;
    433 		}
    434 		srk->key = key;
    435 		key = NULL;
    436 		srk->user_id = userid;
    437 		srk->user_id_len = userid_len;
    438 		userid = NULL;
    439 		userid_len = 0;
    440 		if ((tmp = recallocarray(srks, nsrks, nsrks + 1,
    441 		    sizeof(*srks))) == NULL) {
    442 			error_f("recallocarray keys failed");
    443 			goto out;
    444 		}
    445 		debug_f("srks[%zu]: %s %s uidlen %zu", nsrks,
    446 		    sshkey_type(srk->key), srk->key->sk_application,
    447 		    srk->user_id_len);
    448 		srks = tmp;
    449 		srks[nsrks++] = srk;
    450 		srk = NULL;
    451 	}
    452 
    453 	/* success */
    454 	r = 0;
    455 	*srksp = srks;
    456 	*nsrksp = nsrks;
    457 	srks = NULL;
    458 	nsrks = 0;
    459  out:
    460 	oerrno = errno;
    461 	sshsk_free_resident_key(srk);
    462 	sshsk_free_resident_keys(srks, nsrks);
    463 	freezero(userid, userid_len);
    464 	sshkey_free(key);
    465 	sshbuf_free(kbuf);
    466 	sshbuf_free(req);
    467 	sshbuf_free(resp);
    468 	errno = oerrno;
    469 	return r;
    470 }
    471