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When downloading resident keys from a FIDO token, pass back the
user ID that was used when the key was created and append it to
the filename the key is written to (if it is not the default).

Avoids keys being clobbered if the user created multiple
resident keys with the same application string but different
user IDs.

feedback Pedro Martelletto; ok markus

NB. increments SSH_SK_VERSION_MAJOR

/* $OpenBSD: ssh-sk-client.c,v 1.10 2021/10/28 02:54:18 djm Exp $ */
/*
 * Copyright (c) 2019 Google LLC
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>

#include <fcntl.h>
#include <limits.h>
#include <errno.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "log.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "sshkey.h"
#include "msg.h"
#include "digest.h"
#include "pathnames.h"
#include "ssh-sk.h"
#include "misc.h"

/* #define DEBUG_SK 1 */

static int
start_helper(int *fdp, pid_t *pidp, void (**osigchldp)(int))
{
	void (*osigchld)(int);
	int oerrno, pair[2];
	pid_t pid;
	char *helper, *verbosity = NULL;

	*fdp = -1;
	*pidp = 0;
	*osigchldp = SIG_DFL;

	helper = getenv("SSH_SK_HELPER");
	if (helper == NULL || strlen(helper) == 0)
		helper = _PATH_SSH_SK_HELPER;
	if (access(helper, X_OK) != 0) {
		oerrno = errno;
		error_f("helper \"%s\" unusable: %s", helper, strerror(errno));
		errno = oerrno;
		return SSH_ERR_SYSTEM_ERROR;
	}
#ifdef DEBUG_SK
	verbosity = "-vvv";
#endif

	/* Start helper */
	if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
		error("socketpair: %s", strerror(errno));
		return SSH_ERR_SYSTEM_ERROR;
	}
	osigchld = ssh_signal(SIGCHLD, SIG_DFL);
	if ((pid = fork()) == -1) {
		oerrno = errno;
		error("fork: %s", strerror(errno));
		close(pair[0]);
		close(pair[1]);
		ssh_signal(SIGCHLD, osigchld);
		errno = oerrno;
		return SSH_ERR_SYSTEM_ERROR;
	}
	if (pid == 0) {
		if ((dup2(pair[1], STDIN_FILENO) == -1) ||
		    (dup2(pair[1], STDOUT_FILENO) == -1)) {
			error_f("dup2: %s", strerror(errno));
			_exit(1);
		}
		close(pair[0]);
		close(pair[1]);
		closefrom(STDERR_FILENO + 1);
		debug_f("starting %s %s", helper,
		    verbosity == NULL ? "" : verbosity);
		execlp(helper, helper, verbosity, (char *)NULL);
		error_f("execlp: %s", strerror(errno));
		_exit(1);
	}
	close(pair[1]);

	/* success */
	debug3_f("started pid=%ld", (long)pid);
	*fdp = pair[0];
	*pidp = pid;
	*osigchldp = osigchld;
	return 0;
}

static int
reap_helper(pid_t pid)
{
	int status, oerrno;

	debug3_f("pid=%ld", (long)pid);

	errno = 0;
	while (waitpid(pid, &status, 0) == -1) {
		if (errno == EINTR) {
			errno = 0;
			continue;
		}
		oerrno = errno;
		error_f("waitpid: %s", strerror(errno));
		errno = oerrno;
		return SSH_ERR_SYSTEM_ERROR;
	}
	if (!WIFEXITED(status)) {
		error_f("helper exited abnormally");
		return SSH_ERR_AGENT_FAILURE;
	} else if (WEXITSTATUS(status) != 0) {
		error_f("helper exited with non-zero exit status");
		return SSH_ERR_AGENT_FAILURE;
	}
	return 0;
}

static int
client_converse(struct sshbuf *msg, struct sshbuf **respp, u_int type)
{
	int oerrno, fd, r2, ll, r = SSH_ERR_INTERNAL_ERROR;
	u_int rtype, rerr;
	pid_t pid;
	u_char version;
	void (*osigchld)(int);
	struct sshbuf *req = NULL, *resp = NULL;
	*respp = NULL;

	if ((r = start_helper(&fd, &pid, &osigchld)) != 0)
		return r;

	if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL) {
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}
	/* Request preamble: type, log_on_stderr, log_level */
	ll = log_level_get();
	if ((r = sshbuf_put_u32(req, type)) != 0 ||
	    (r = sshbuf_put_u8(req, log_is_on_stderr() != 0)) != 0 ||
	    (r = sshbuf_put_u32(req, ll < 0 ? 0 : ll)) != 0 ||
	    (r = sshbuf_putb(req, msg)) != 0) {
		error_fr(r, "compose");
		goto out;
	}
	if ((r = ssh_msg_send(fd, SSH_SK_HELPER_VERSION, req)) != 0) {
		error_fr(r, "send");
		goto out;
	}
	if ((r = ssh_msg_recv(fd, resp)) != 0) {
		error_fr(r, "receive");
		goto out;
	}
	if ((r = sshbuf_get_u8(resp, &version)) != 0) {
		error_fr(r, "parse version");
		goto out;
	}
	if (version != SSH_SK_HELPER_VERSION) {
		error_f("unsupported version: got %u, expected %u",
		    version, SSH_SK_HELPER_VERSION);
		r = SSH_ERR_INVALID_FORMAT;
		goto out;
	}
	if ((r = sshbuf_get_u32(resp, &rtype)) != 0) {
		error_fr(r, "parse message type");
		goto out;
	}
	if (rtype == SSH_SK_HELPER_ERROR) {
		if ((r = sshbuf_get_u32(resp, &rerr)) != 0) {
			error_fr(r, "parse");
			goto out;
		}
		debug_f("helper returned error -%u", rerr);
		/* OpenSSH error values are negative; encoded as -err on wire */
		if (rerr == 0 || rerr >= INT_MAX)
			r = SSH_ERR_INTERNAL_ERROR;
		else
			r = -(int)rerr;
		goto out;
	} else if (rtype != type) {
		error_f("helper returned incorrect message type %u, "
		    "expecting %u", rtype, type);
		r = SSH_ERR_INTERNAL_ERROR;
		goto out;
	}
	/* success */
	r = 0;
 out:
	oerrno = errno;
	close(fd);
	if ((r2 = reap_helper(pid)) != 0) {
		if (r == 0) {
			r = r2;
			oerrno = errno;
		}
	}
	if (r == 0) {
		*respp = resp;
		resp = NULL;
	}
	sshbuf_free(req);
	sshbuf_free(resp);
	ssh_signal(SIGCHLD, osigchld);
	errno = oerrno;
	return r;

}

int
sshsk_sign(const char *provider, struct sshkey *key,
    u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
    u_int compat, const char *pin)
{
	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
	char *fp = NULL;
	struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;

	*sigp = NULL;
	*lenp = 0;

	if ((kbuf = sshbuf_new()) == NULL ||
	    (req = sshbuf_new()) == NULL) {
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}

	if ((r = sshkey_private_serialize(key, kbuf)) != 0) {
		error_fr(r, "encode key");
		goto out;
	}
	if ((r = sshbuf_put_stringb(req, kbuf)) != 0 ||
	    (r = sshbuf_put_cstring(req, provider)) != 0 ||
	    (r = sshbuf_put_string(req, data, datalen)) != 0 ||
	    (r = sshbuf_put_cstring(req, NULL)) != 0 || /* alg */
	    (r = sshbuf_put_u32(req, compat)) != 0 ||
	    (r = sshbuf_put_cstring(req, pin)) != 0) {
		error_fr(r, "compose");
		goto out;
	}

	if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
	    SSH_FP_DEFAULT)) == NULL) {
		error_f("sshkey_fingerprint failed");
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}
	if ((r = client_converse(req, &resp, SSH_SK_HELPER_SIGN)) != 0)
		goto out;

	if ((r = sshbuf_get_string(resp, sigp, lenp)) != 0) {
		error_fr(r, "parse signature");
		r = SSH_ERR_INVALID_FORMAT;
		goto out;
	}
	if (sshbuf_len(resp) != 0) {
		error_f("trailing data in response");
		r = SSH_ERR_INVALID_FORMAT;
		goto out;
	}
	/* success */
	r = 0;
 out:
	oerrno = errno;
	if (r != 0) {
		freezero(*sigp, *lenp);
		*sigp = NULL;
		*lenp = 0;
	}
	sshbuf_free(kbuf);
	sshbuf_free(req);
	sshbuf_free(resp);
	errno = oerrno;
	return r;
}

int
sshsk_enroll(int type, const char *provider_path, const char *device,
    const char *application, const char *userid, uint8_t flags,
    const char *pin, struct sshbuf *challenge_buf,
    struct sshkey **keyp, struct sshbuf *attest)
{
	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
	struct sshbuf *kbuf = NULL, *abuf = NULL, *req = NULL, *resp = NULL;
	struct sshkey *key = NULL;

	*keyp = NULL;
	if (attest != NULL)
		sshbuf_reset(attest);

	if (type < 0)
		return SSH_ERR_INVALID_ARGUMENT;

	if ((abuf = sshbuf_new()) == NULL ||
	    (kbuf = sshbuf_new()) == NULL ||
	    (req = sshbuf_new()) == NULL) {
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}

	if ((r = sshbuf_put_u32(req, (u_int)type)) != 0 ||
	    (r = sshbuf_put_cstring(req, provider_path)) != 0 ||
	    (r = sshbuf_put_cstring(req, device)) != 0 ||
	    (r = sshbuf_put_cstring(req, application)) != 0 ||
	    (r = sshbuf_put_cstring(req, userid)) != 0 ||
	    (r = sshbuf_put_u8(req, flags)) != 0 ||
	    (r = sshbuf_put_cstring(req, pin)) != 0 ||
	    (r = sshbuf_put_stringb(req, challenge_buf)) != 0) {
		error_fr(r, "compose");
		goto out;
	}

	if ((r = client_converse(req, &resp, SSH_SK_HELPER_ENROLL)) != 0)
		goto out;

	if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
	    (r = sshbuf_get_stringb(resp, abuf)) != 0) {
		error_fr(r, "parse");
		r = SSH_ERR_INVALID_FORMAT;
		goto out;
	}
	if (sshbuf_len(resp) != 0) {
		error_f("trailing data in response");
		r = SSH_ERR_INVALID_FORMAT;
		goto out;
	}
	if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
		error_fr(r, "encode");
		goto out;
	}
	if (attest != NULL && (r = sshbuf_putb(attest, abuf)) != 0) {
		error_fr(r, "encode attestation information");
		goto out;
	}

	/* success */
	r = 0;
	*keyp = key;
	key = NULL;
 out:
	oerrno = errno;
	sshkey_free(key);
	sshbuf_free(kbuf);
	sshbuf_free(abuf);
	sshbuf_free(req);
	sshbuf_free(resp);
	errno = oerrno;
	return r;
}

static void
sshsk_free_resident_key(struct sshsk_resident_key *srk)
{
	if (srk == NULL)
		return;
	sshkey_free(srk->key);
	freezero(srk->user_id, srk->user_id_len);
	free(srk);
}


void
sshsk_free_resident_keys(struct sshsk_resident_key **srks, size_t nsrks)
{
	size_t i;

	if (srks == NULL || nsrks == 0)
		return;

	for (i = 0; i < nsrks; i++)
		sshsk_free_resident_key(srks[i]);
	free(srks);
}

int
sshsk_load_resident(const char *provider_path, const char *device,
    const char *pin, u_int flags, struct sshsk_resident_key ***srksp,
    size_t *nsrksp)
{
	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
	struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
	struct sshkey *key = NULL;
	struct sshsk_resident_key *srk = NULL, **srks = NULL, **tmp;
	u_char *userid = NULL;
	size_t userid_len = 0, nsrks = 0;

	*srksp = NULL;
	*nsrksp = 0;

	if ((resp = sshbuf_new()) == NULL ||
	    (kbuf = sshbuf_new()) == NULL ||
	    (req = sshbuf_new()) == NULL) {
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}

	if ((r = sshbuf_put_cstring(req, provider_path)) != 0 ||
	    (r = sshbuf_put_cstring(req, device)) != 0 ||
	    (r = sshbuf_put_cstring(req, pin)) != 0 ||
	    (r = sshbuf_put_u32(req, flags)) != 0) {
		error_fr(r, "compose");
		goto out;
	}

	if ((r = client_converse(req, &resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
		goto out;

	while (sshbuf_len(resp) != 0) {
		/* key, comment, user_id */
		if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
		    (r = sshbuf_get_cstring(resp, NULL, NULL)) != 0 ||
		    (r = sshbuf_get_string(resp, &userid, &userid_len)) != 0) {
			error_fr(r, "parse");
			r = SSH_ERR_INVALID_FORMAT;
			goto out;
		}
		if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
			error_fr(r, "decode key");
			goto out;
		}
		if ((srk = calloc(1, sizeof(*srk))) == NULL) {
			error_f("calloc failed");
			goto out;
		}
		srk->key = key;
		key = NULL;
		srk->user_id = userid;
		srk->user_id_len = userid_len;
		userid = NULL;
		userid_len = 0;
		if ((tmp = recallocarray(srks, nsrks, nsrks + 1,
		    sizeof(*srks))) == NULL) {
			error_f("recallocarray keys failed");
			goto out;
		}
		debug_f("srks[%zu]: %s %s uidlen %zu", nsrks,
		    sshkey_type(srk->key), srk->key->sk_application,
		    srk->user_id_len);
		srks = tmp;
		srks[nsrks++] = srk;
		srk = NULL;
	}

	/* success */
	r = 0;
	*srksp = srks;
	*nsrksp = nsrks;
	srks = NULL;
	nsrks = 0;
 out:
	oerrno = errno;
	sshsk_free_resident_key(srk);
	sshsk_free_resident_keys(srks, nsrks);
	freezero(userid, userid_len);
	sshkey_free(key);
	sshbuf_free(kbuf);
	sshbuf_free(req);
	sshbuf_free(resp);
	errno = oerrno;
	return r;
}