/* $OpenBSD: auth-options.c,v 1.101 2023/07/14 07:44:21 dtucker Exp $ */
/*
 * Copyright (c) 2018 Damien Miller <djm@mindrot.org>
 *
 * 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 "includes.h"

#include <sys/types.h>

#include <stdlib.h>
#include <netdb.h>
#include <pwd.h>
#include <string.h>
#include <stdio.h>
#ifdef HAVE_STDINT_H
# include <stdint.h>
#endif
#include <stdarg.h>
#include <ctype.h>
#include <limits.h>

#include "openbsd-compat/sys-queue.h"

#include "xmalloc.h"
#include "ssherr.h"
#include "log.h"
#include "sshbuf.h"
#include "misc.h"
#include "sshkey.h"
#include "match.h"
#include "ssh2.h"
#include "auth-options.h"

static int
dup_strings(char ***dstp, size_t *ndstp, char **src, size_t nsrc)
{
        char **dst;
        size_t i, j;

        *dstp = NULL;
        *ndstp = 0;

        if (nsrc == 0)
                return 0;
        if (nsrc >= SIZE_MAX / sizeof(*src) ||
            (dst = calloc(nsrc, sizeof(*src))) == NULL)
                return -1;
        for (i = 0; i < nsrc; i++) {
                if ((dst[i] = strdup(src[i])) == NULL) {
                        for (j = 0; j < i; j++)
                                free(dst[j]);
                        free(dst);
                        return -1;
                }
        }
        /* success */
        *dstp = dst;
        *ndstp = nsrc;
        return 0;
}

#define OPTIONS_CRITICAL        1
#define OPTIONS_EXTENSIONS      2
static int
cert_option_list(struct sshauthopt *opts, struct sshbuf *oblob,
    u_int which, int crit)
{
        char *command, *allowed;
        char *name = NULL;
        struct sshbuf *c = NULL, *data = NULL;
        int r, ret = -1, found;

        if ((c = sshbuf_fromb(oblob)) == NULL) {
                error_f("sshbuf_fromb failed");
                goto out;
        }

        while (sshbuf_len(c) > 0) {
                sshbuf_free(data);
                data = NULL;
                if ((r = sshbuf_get_cstring(c, &name, NULL)) != 0 ||
                    (r = sshbuf_froms(c, &data)) != 0) {
                        error_r(r, "Unable to parse certificate options");
                        goto out;
                }
                debug3("found certificate option \"%.100s\" len %zu",
                    name, sshbuf_len(data));
                found = 0;
                if ((which & OPTIONS_EXTENSIONS) != 0) {
                        if (strcmp(name, "no-touch-required") == 0) {
                                opts->no_require_user_presence = 1;
                                found = 1;
                        } else if (strcmp(name, "permit-X11-forwarding") == 0) {
                                opts->permit_x11_forwarding_flag = 1;
                                found = 1;
                        } else if (strcmp(name,
                            "permit-agent-forwarding") == 0) {
                                opts->permit_agent_forwarding_flag = 1;
                                found = 1;
                        } else if (strcmp(name,
                            "permit-port-forwarding") == 0) {
                                opts->permit_port_forwarding_flag = 1;
                                found = 1;
                        } else if (strcmp(name, "permit-pty") == 0) {
                                opts->permit_pty_flag = 1;
                                found = 1;
                        } else if (strcmp(name, "permit-user-rc") == 0) {
                                opts->permit_user_rc = 1;
                                found = 1;
                        }
                }
                if (!found && (which & OPTIONS_CRITICAL) != 0) {
                        if (strcmp(name, "verify-required") == 0) {
                                opts->require_verify = 1;
                                found = 1;
                        } else if (strcmp(name, "force-command") == 0) {
                                if ((r = sshbuf_get_cstring(data, &command,
                                    NULL)) != 0) {
                                        error_r(r, "Unable to parse \"%s\" "
                                            "section", name);
                                        goto out;
                                }
                                if (opts->force_command != NULL) {
                                        error("Certificate has multiple "
                                            "force-command options");
                                        free(command);
                                        goto out;
                                }
                                opts->force_command = command;
                                found = 1;
                        } else if (strcmp(name, "source-address") == 0) {
                                if ((r = sshbuf_get_cstring(data, &allowed,
                                    NULL)) != 0) {
                                        error_r(r, "Unable to parse \"%s\" "
                                            "section", name);
                                        goto out;
                                }
                                if (opts->required_from_host_cert != NULL) {
                                        error("Certificate has multiple "
                                            "source-address options");
                                        free(allowed);
                                        goto out;
                                }
                                /* Check syntax */
                                if (addr_match_cidr_list(NULL, allowed) == -1) {
                                        error("Certificate source-address "
                                            "contents invalid");
                                        goto out;
                                }
                                opts->required_from_host_cert = allowed;
                                found = 1;
                        }
                }

                if (!found) {
                        if (crit) {
                                error("Certificate critical option \"%s\" "
                                    "is not supported", name);
                                goto out;
                        } else {
                                logit("Certificate extension \"%s\" "
                                    "is not supported", name);
                        }
                } else if (sshbuf_len(data) != 0) {
                        error("Certificate option \"%s\" corrupt "
                            "(extra data)", name);
                        goto out;
                }
                free(name);
                name = NULL;
        }
        /* successfully parsed all options */
        ret = 0;

 out:
        free(name);
        sshbuf_free(data);
        sshbuf_free(c);
        return ret;
}

struct sshauthopt *
sshauthopt_new(void)
{
        struct sshauthopt *ret;

        if ((ret = calloc(1, sizeof(*ret))) == NULL)
                return NULL;
        ret->force_tun_device = -1;
        return ret;
}

void
sshauthopt_free(struct sshauthopt *opts)
{
        size_t i;

        if (opts == NULL)
                return;

        free(opts->cert_principals);
        free(opts->force_command);
        free(opts->required_from_host_cert);
        free(opts->required_from_host_keys);

        for (i = 0; i < opts->nenv; i++)
                free(opts->env[i]);
        free(opts->env);

        for (i = 0; i < opts->npermitopen; i++)
                free(opts->permitopen[i]);
        free(opts->permitopen);

        for (i = 0; i < opts->npermitlisten; i++)
                free(opts->permitlisten[i]);
        free(opts->permitlisten);

        freezero(opts, sizeof(*opts));
}

struct sshauthopt *
sshauthopt_new_with_keys_defaults(void)
{
        struct sshauthopt *ret = NULL;

        if ((ret = sshauthopt_new()) == NULL)
                return NULL;

        /* Defaults for authorized_keys flags */
        ret->permit_port_forwarding_flag = 1;
        ret->permit_agent_forwarding_flag = 1;
        ret->permit_x11_forwarding_flag = 1;
        ret->permit_pty_flag = 1;
        ret->permit_user_rc = 1;
        return ret;
}

/*
 * Parse and record a permitopen/permitlisten directive.
 * Return 0 on success. Return -1 on failure and sets *errstrp to error reason.
 */
static int
handle_permit(const char **optsp, int allow_bare_port,
    char ***permitsp, size_t *npermitsp, const char **errstrp)
{
        char *opt, *tmp, *cp, *host, **permits = *permitsp;
        size_t npermits = *npermitsp;
        const char *errstr = "unknown error";

        if (npermits > SSH_AUTHOPT_PERMIT_MAX) {
                *errstrp = "too many permission directives";
                return -1;
        }
        if ((opt = opt_dequote(optsp, &errstr)) == NULL) {
                return -1;
        }
        if (allow_bare_port && strchr(opt, ':') == NULL) {
                /*
                 * Allow a bare port number in permitlisten to indicate a
                 * listen_host wildcard.
                 */
                if (asprintf(&tmp, "*:%s", opt) == -1) {
                        free(opt);
                        *errstrp = "memory allocation failed";
                        return -1;
                }
                free(opt);
                opt = tmp;
        }
        if ((tmp = strdup(opt)) == NULL) {
                free(opt);
                *errstrp = "memory allocation failed";
                return -1;
        }
        cp = tmp;
        /* validate syntax before recording it. */
        host = hpdelim2(&cp, NULL);
        if (host == NULL || strlen(host) >= NI_MAXHOST) {
                free(tmp);
                free(opt);
                *errstrp = "invalid permission hostname";
                return -1;
        }
        /*
         * don't want to use permitopen_port to avoid
         * dependency on channels.[ch] here.
         */
        if (cp == NULL ||
            (strcmp(cp, "*") != 0 && a2port(cp) <= 0)) {
                free(tmp);
                free(opt);
                *errstrp = "invalid permission port";
                return -1;
        }
        /* XXX - add streamlocal support */
        free(tmp);
        /* Record it */
        if ((permits = recallocarray(permits, npermits, npermits + 1,
            sizeof(*permits))) == NULL) {
                free(opt);
                /* NB. don't update *permitsp if alloc fails */
                *errstrp = "memory allocation failed";
                return -1;
        }
        permits[npermits++] = opt;
        *permitsp = permits;
        *npermitsp = npermits;
        return 0;
}

struct sshauthopt *
sshauthopt_parse(const char *opts, const char **errstrp)
{
        char **oarray, *opt, *cp, *tmp;
        int r;
        struct sshauthopt *ret = NULL;
        const char *errstr = "unknown error";
        uint64_t valid_before;
        size_t i, l;

        if (errstrp != NULL)
                *errstrp = NULL;
        if ((ret = sshauthopt_new_with_keys_defaults()) == NULL)
                goto alloc_fail;

        if (opts == NULL)
                return ret;

        while (*opts && *opts != ' ' && *opts != '\t') {
                /* flag options */
                if ((r = opt_flag("restrict", 0, &opts)) != -1) {
                        ret->restricted = 1;
                        ret->permit_port_forwarding_flag = 0;
                        ret->permit_agent_forwarding_flag = 0;
                        ret->permit_x11_forwarding_flag = 0;
                        ret->permit_pty_flag = 0;
                        ret->permit_user_rc = 0;
                } else if ((r = opt_flag("cert-authority", 0, &opts)) != -1) {
                        ret->cert_authority = r;
                } else if ((r = opt_flag("port-forwarding", 1, &opts)) != -1) {
                        ret->permit_port_forwarding_flag = r == 1;
                } else if ((r = opt_flag("agent-forwarding", 1, &opts)) != -1) {
                        ret->permit_agent_forwarding_flag = r == 1;
                } else if ((r = opt_flag("x11-forwarding", 1, &opts)) != -1) {
                        ret->permit_x11_forwarding_flag = r == 1;
                } else if ((r = opt_flag("touch-required", 1, &opts)) != -1) {
                        ret->no_require_user_presence = r != 1; /* NB. flip */
                } else if ((r = opt_flag("verify-required", 1, &opts)) != -1) {
                        ret->require_verify = r == 1;
                } else if ((r = opt_flag("pty", 1, &opts)) != -1) {
                        ret->permit_pty_flag = r == 1;
                } else if ((r = opt_flag("user-rc", 1, &opts)) != -1) {
                        ret->permit_user_rc = r == 1;
                } else if (opt_match(&opts, "command")) {
                        if (ret->force_command != NULL) {
                                errstr = "multiple \"command\" clauses";
                                goto fail;
                        }
                        ret->force_command = opt_dequote(&opts, &errstr);
                        if (ret->force_command == NULL)
                                goto fail;
                } else if (opt_match(&opts, "principals")) {
                        if (ret->cert_principals != NULL) {
                                errstr = "multiple \"principals\" clauses";
                                goto fail;
                        }
                        ret->cert_principals = opt_dequote(&opts, &errstr);
                        if (ret->cert_principals == NULL)
                                goto fail;
                } else if (opt_match(&opts, "from")) {
                        if (ret->required_from_host_keys != NULL) {
                                errstr = "multiple \"from\" clauses";
                                goto fail;
                        }
                        ret->required_from_host_keys = opt_dequote(&opts,
                            &errstr);
                        if (ret->required_from_host_keys == NULL)
                                goto fail;
                } else if (opt_match(&opts, "expiry-time")) {
                        if ((opt = opt_dequote(&opts, &errstr)) == NULL)
                                goto fail;
                        if (parse_absolute_time(opt, &valid_before) != 0 ||
                            valid_before == 0) {
                                free(opt);
                                errstr = "invalid expires time";
                                goto fail;
                        }
                        free(opt);
                        if (ret->valid_before == 0 ||
                            valid_before < ret->valid_before)
                                ret->valid_before = valid_before;
                } else if (opt_match(&opts, "environment")) {
                        if (ret->nenv > SSH_AUTHOPT_ENV_MAX) {
                                errstr = "too many environment strings";
                                goto fail;
                        }
                        if ((opt = opt_dequote(&opts, &errstr)) == NULL)
                                goto fail;
                        /* env name must be alphanumeric and followed by '=' */
                        if ((tmp = strchr(opt, '=')) == NULL) {
                                free(opt);
                                errstr = "invalid environment string";
                                goto fail;
                        }
                        if ((cp = strdup(opt)) == NULL) {
                                free(opt);
                                goto alloc_fail;
                        }
                        l = (size_t)(tmp - opt);
                        cp[l] = '\0'; /* truncate at '=' */
                        if (!valid_env_name(cp)) {
                                free(cp);
                                free(opt);
                                errstr = "invalid environment string";
                                goto fail;
                        }
                        /* Check for duplicates; XXX O(n*log(n)) */
                        for (i = 0; i < ret->nenv; i++) {
                                if (strncmp(ret->env[i], cp, l) == 0 &&
                                    ret->env[i][l] == '=')
                                        break;
                        }
                        free(cp);
                        /* First match wins */
                        if (i >= ret->nenv) {
                                /* Append it. */
                                oarray = ret->env;
                                if ((ret->env = recallocarray(ret->env,
                                    ret->nenv, ret->nenv + 1,
                                    sizeof(*ret->env))) == NULL) {
                                        free(opt);
                                        /* put it back for cleanup */
                                        ret->env = oarray;
                                        goto alloc_fail;
                                }
                                ret->env[ret->nenv++] = opt;
                                opt = NULL; /* transferred */
                        }
                        free(opt);
                } else if (opt_match(&opts, "permitopen")) {
                        if (handle_permit(&opts, 0, &ret->permitopen,
                            &ret->npermitopen, &errstr) != 0)
                                goto fail;
                } else if (opt_match(&opts, "permitlisten")) {
                        if (handle_permit(&opts, 1, &ret->permitlisten,
                            &ret->npermitlisten, &errstr) != 0)
                                goto fail;
                } else if (opt_match(&opts, "tunnel")) {
                        if ((opt = opt_dequote(&opts, &errstr)) == NULL)
                                goto fail;
                        ret->force_tun_device = a2tun(opt, NULL);
                        free(opt);
                        if (ret->force_tun_device == SSH_TUNID_ERR) {
                                errstr = "invalid tun device";
                                goto fail;
                        }
                }
                /*
                 * Skip the comma, and move to the next option
                 * (or break out if there are no more).
                 */
                if (*opts == '\0' || *opts == ' ' || *opts == '\t')
                        break;          /* End of options. */
                /* Anything other than a comma is an unknown option */
                if (*opts != ',') {
                        errstr = "unknown key option";
                        goto fail;
                }
                opts++;
                if (*opts == '\0') {
                        errstr = "unexpected end-of-options";
                        goto fail;
                }
        }

        /* success */
        if (errstrp != NULL)
                *errstrp = NULL;
        return ret;

alloc_fail:
        errstr = "memory allocation failed";
fail:
        sshauthopt_free(ret);
        if (errstrp != NULL)
                *errstrp = errstr;
        return NULL;
}

struct sshauthopt *
sshauthopt_from_cert(struct sshkey *k)
{
        struct sshauthopt *ret;

        if (k == NULL || !sshkey_type_is_cert(k->type) || k->cert == NULL ||
            k->cert->type != SSH2_CERT_TYPE_USER)
                return NULL;

        if ((ret = sshauthopt_new()) == NULL)
                return NULL;

        /* Handle options and critical extensions separately */
        if (cert_option_list(ret, k->cert->critical,
            OPTIONS_CRITICAL, 1) == -1) {
                sshauthopt_free(ret);
                return NULL;
        }
        if (cert_option_list(ret, k->cert->extensions,
            OPTIONS_EXTENSIONS, 0) == -1) {
                sshauthopt_free(ret);
                return NULL;
        }
        /* success */
        return ret;
}

/*
 * Merges "additional" options to "primary" and returns the result.
 * NB. Some options from primary have primacy.
 */
struct sshauthopt *
sshauthopt_merge(const struct sshauthopt *primary,
    const struct sshauthopt *additional, const char **errstrp)
{
        struct sshauthopt *ret;
        const char *errstr = "internal error";
        const char *tmp;

        if (errstrp != NULL)
                *errstrp = NULL;

        if ((ret = sshauthopt_new()) == NULL)
                goto alloc_fail;

        /* cert_authority and cert_principals are cleared in result */

        /* Prefer access lists from primary. */
        /* XXX err is both set and mismatch? */
        tmp = primary->required_from_host_cert;
        if (tmp == NULL)
                tmp = additional->required_from_host_cert;
        if (tmp != NULL && (ret->required_from_host_cert = strdup(tmp)) == NULL)
                goto alloc_fail;
        tmp = primary->required_from_host_keys;
        if (tmp == NULL)
                tmp = additional->required_from_host_keys;
        if (tmp != NULL && (ret->required_from_host_keys = strdup(tmp)) == NULL)
                goto alloc_fail;

        /*
         * force_tun_device, permitopen/permitlisten and environment all
         * prefer the primary.
         */
        ret->force_tun_device = primary->force_tun_device;
        if (ret->force_tun_device == -1)
                ret->force_tun_device = additional->force_tun_device;
        if (primary->nenv > 0) {
                if (dup_strings(&ret->env, &ret->nenv,
                    primary->env, primary->nenv) != 0)
                        goto alloc_fail;
        } else if (additional->nenv) {
                if (dup_strings(&ret->env, &ret->nenv,
                    additional->env, additional->nenv) != 0)
                        goto alloc_fail;
        }
        if (primary->npermitopen > 0) {
                if (dup_strings(&ret->permitopen, &ret->npermitopen,
                    primary->permitopen, primary->npermitopen) != 0)
                        goto alloc_fail;
        } else if (additional->npermitopen > 0) {
                if (dup_strings(&ret->permitopen, &ret->npermitopen,
                    additional->permitopen, additional->npermitopen) != 0)
                        goto alloc_fail;
        }

        if (primary->npermitlisten > 0) {
                if (dup_strings(&ret->permitlisten, &ret->npermitlisten,
                    primary->permitlisten, primary->npermitlisten) != 0)
                        goto alloc_fail;
        } else if (additional->npermitlisten > 0) {
                if (dup_strings(&ret->permitlisten, &ret->npermitlisten,
                    additional->permitlisten, additional->npermitlisten) != 0)
                        goto alloc_fail;
        }

#define OPTFLAG_AND(x) ret->x = (primary->x == 1) && (additional->x == 1)
#define OPTFLAG_OR(x) ret->x = (primary->x == 1) || (additional->x == 1)
        /* Permissive flags are logical-AND (i.e. must be set in both) */
        OPTFLAG_AND(permit_port_forwarding_flag);
        OPTFLAG_AND(permit_agent_forwarding_flag);
        OPTFLAG_AND(permit_x11_forwarding_flag);
        OPTFLAG_AND(permit_pty_flag);
        OPTFLAG_AND(permit_user_rc);
        OPTFLAG_AND(no_require_user_presence);
        /* Restrictive flags are logical-OR (i.e. must be set in either) */
        OPTFLAG_OR(require_verify);
#undef OPTFLAG_AND

        /* Earliest expiry time should win */
        if (primary->valid_before != 0)
                ret->valid_before = primary->valid_before;
        if (additional->valid_before != 0 &&
            additional->valid_before < ret->valid_before)
                ret->valid_before = additional->valid_before;

        /*
         * When both multiple forced-command are specified, only
         * proceed if they are identical, otherwise fail.
         */
        if (primary->force_command != NULL &&
            additional->force_command != NULL) {
                if (strcmp(primary->force_command,
                    additional->force_command) == 0) {
                        /* ok */
                        ret->force_command = strdup(primary->force_command);
                        if (ret->force_command == NULL)
                                goto alloc_fail;
                } else {
                        errstr = "forced command options do not match";
                        goto fail;
                }
        } else if (primary->force_command != NULL) {
                if ((ret->force_command = strdup(
                    primary->force_command)) == NULL)
                        goto alloc_fail;
        } else if (additional->force_command != NULL) {
                if ((ret->force_command = strdup(
                    additional->force_command)) == NULL)
                        goto alloc_fail;
        }
        /* success */
        if (errstrp != NULL)
                *errstrp = NULL;
        return ret;

 alloc_fail:
        errstr = "memory allocation failed";
 fail:
        if (errstrp != NULL)
                *errstrp = errstr;
        sshauthopt_free(ret);
        return NULL;
}

/*
 * Copy options
 */
struct sshauthopt *
sshauthopt_copy(const struct sshauthopt *orig)
{
        struct sshauthopt *ret;

        if ((ret = sshauthopt_new()) == NULL)
                return NULL;

#define OPTSCALAR(x) ret->x = orig->x
        OPTSCALAR(permit_port_forwarding_flag);
        OPTSCALAR(permit_agent_forwarding_flag);
        OPTSCALAR(permit_x11_forwarding_flag);
        OPTSCALAR(permit_pty_flag);
        OPTSCALAR(permit_user_rc);
        OPTSCALAR(restricted);
        OPTSCALAR(cert_authority);
        OPTSCALAR(force_tun_device);
        OPTSCALAR(valid_before);
        OPTSCALAR(no_require_user_presence);
        OPTSCALAR(require_verify);
#undef OPTSCALAR
#define OPTSTRING(x) \
        do { \
                if (orig->x != NULL && (ret->x = strdup(orig->x)) == NULL) { \
                        sshauthopt_free(ret); \
                        return NULL; \
                } \
        } while (0)
        OPTSTRING(cert_principals);
        OPTSTRING(force_command);
        OPTSTRING(required_from_host_cert);
        OPTSTRING(required_from_host_keys);
#undef OPTSTRING

        if (dup_strings(&ret->env, &ret->nenv, orig->env, orig->nenv) != 0 ||
            dup_strings(&ret->permitopen, &ret->npermitopen,
            orig->permitopen, orig->npermitopen) != 0 ||
            dup_strings(&ret->permitlisten, &ret->npermitlisten,
            orig->permitlisten, orig->npermitlisten) != 0) {
                sshauthopt_free(ret);
                return NULL;
        }
        return ret;
}

static int
serialise_array(struct sshbuf *m, char **a, size_t n)
{
        struct sshbuf *b;
        size_t i;
        int r = SSH_ERR_INTERNAL_ERROR;

        if (n > INT_MAX)
                return SSH_ERR_INTERNAL_ERROR;

        if ((b = sshbuf_new()) == NULL) {
                return SSH_ERR_ALLOC_FAIL;
        }
        for (i = 0; i < n; i++) {
                if ((r = sshbuf_put_cstring(b, a[i])) != 0)
                        goto out;
        }
        if ((r = sshbuf_put_u32(m, n)) != 0 ||
            (r = sshbuf_put_stringb(m, b)) != 0)
                goto out;
        /* success */
        r = 0;
 out:
        sshbuf_free(b);
        return r;
}

static int
deserialise_array(struct sshbuf *m, char ***ap, size_t *np)
{
        char **a = NULL;
        size_t i, n = 0;
        struct sshbuf *b = NULL;
        u_int tmp;
        int r = SSH_ERR_INTERNAL_ERROR;

        if ((r = sshbuf_get_u32(m, &tmp)) != 0 ||
            (r = sshbuf_froms(m, &b)) != 0)
                goto out;
        if (tmp > INT_MAX) {
                r = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        n = tmp;
        if (n > 0 && (a = calloc(n, sizeof(*a))) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }
        for (i = 0; i < n; i++) {
                if ((r = sshbuf_get_cstring(b, &a[i], NULL)) != 0)
                        goto out;
        }
        /* success */
        r = 0;
        *ap = a;
        a = NULL;
        *np = n;
        n = 0;
 out:
        if (a != NULL) {
                for (i = 0; i < n; i++)
                        free(a[i]);
                free(a);
        }
        sshbuf_free(b);
        return r;
}

static int
serialise_nullable_string(struct sshbuf *m, const char *s)
{
        int r;

        if ((r = sshbuf_put_u8(m, s == NULL)) != 0 ||
            (r = sshbuf_put_cstring(m, s)) != 0)
                return r;
        return 0;
}

static int
deserialise_nullable_string(struct sshbuf *m, char **sp)
{
        int r;
        u_char flag;

        *sp = NULL;
        if ((r = sshbuf_get_u8(m, &flag)) != 0 ||
            (r = sshbuf_get_cstring(m, flag ? NULL : sp, NULL)) != 0)
                return r;
        return 0;
}

int
sshauthopt_serialise(const struct sshauthopt *opts, struct sshbuf *m,
    int untrusted)
{
        int r = SSH_ERR_INTERNAL_ERROR;

        /* Flag options */
        if ((r = sshbuf_put_u8(m, opts->permit_port_forwarding_flag)) != 0 ||
            (r = sshbuf_put_u8(m, opts->permit_agent_forwarding_flag)) != 0 ||
            (r = sshbuf_put_u8(m, opts->permit_x11_forwarding_flag)) != 0 ||
            (r = sshbuf_put_u8(m, opts->permit_pty_flag)) != 0 ||
            (r = sshbuf_put_u8(m, opts->permit_user_rc)) != 0 ||
            (r = sshbuf_put_u8(m, opts->restricted)) != 0 ||
            (r = sshbuf_put_u8(m, opts->cert_authority)) != 0 ||
            (r = sshbuf_put_u8(m, opts->no_require_user_presence)) != 0 ||
            (r = sshbuf_put_u8(m, opts->require_verify)) != 0)
                return r;

        /* Simple integer options */
        if ((r = sshbuf_put_u64(m, opts->valid_before)) != 0)
                return r;

        /* tunnel number can be negative to indicate "unset" */
        if ((r = sshbuf_put_u8(m, opts->force_tun_device == -1)) != 0 ||
            (r = sshbuf_put_u32(m, (opts->force_tun_device < 0) ?
            0 : (u_int)opts->force_tun_device)) != 0)
                return r;

        /* String options; these may be NULL */
        if ((r = serialise_nullable_string(m,
            untrusted ? "yes" : opts->cert_principals)) != 0 ||
            (r = serialise_nullable_string(m,
            untrusted ? "true" : opts->force_command)) != 0 ||
            (r = serialise_nullable_string(m,
            untrusted ? NULL : opts->required_from_host_cert)) != 0 ||
            (r = serialise_nullable_string(m,
            untrusted ? NULL : opts->required_from_host_keys)) != 0)
                return r;

        /* Array options */
        if ((r = serialise_array(m, opts->env,
            untrusted ? 0 : opts->nenv)) != 0 ||
            (r = serialise_array(m, opts->permitopen,
            untrusted ? 0 : opts->npermitopen)) != 0 ||
            (r = serialise_array(m, opts->permitlisten,
            untrusted ? 0 : opts->npermitlisten)) != 0)
                return r;

        /* success */
        return 0;
}

int
sshauthopt_deserialise(struct sshbuf *m, struct sshauthopt **optsp)
{
        struct sshauthopt *opts = NULL;
        int r = SSH_ERR_INTERNAL_ERROR;
        u_char f;
        u_int tmp;

        if ((opts = calloc(1, sizeof(*opts))) == NULL)
                return SSH_ERR_ALLOC_FAIL;

        /* Flag options */
#define OPT_FLAG(x) \
        do { \
                if ((r = sshbuf_get_u8(m, &f)) != 0) \
                        goto out; \
                opts->x = f; \
        } while (0)
        OPT_FLAG(permit_port_forwarding_flag);
        OPT_FLAG(permit_agent_forwarding_flag);
        OPT_FLAG(permit_x11_forwarding_flag);
        OPT_FLAG(permit_pty_flag);
        OPT_FLAG(permit_user_rc);
        OPT_FLAG(restricted);
        OPT_FLAG(cert_authority);
        OPT_FLAG(no_require_user_presence);
        OPT_FLAG(require_verify);
#undef OPT_FLAG

        /* Simple integer options */
        if ((r = sshbuf_get_u64(m, &opts->valid_before)) != 0)
                goto out;

        /* tunnel number can be negative to indicate "unset" */
        if ((r = sshbuf_get_u8(m, &f)) != 0 ||
            (r = sshbuf_get_u32(m, &tmp)) != 0)
                goto out;
        opts->force_tun_device = f ? -1 : (int)tmp;

        /* String options may be NULL */
        if ((r = deserialise_nullable_string(m, &opts->cert_principals)) != 0 ||
            (r = deserialise_nullable_string(m, &opts->force_command)) != 0 ||
            (r = deserialise_nullable_string(m,
            &opts->required_from_host_cert)) != 0 ||
            (r = deserialise_nullable_string(m,
            &opts->required_from_host_keys)) != 0)
                goto out;

        /* Array options */
        if ((r = deserialise_array(m, &opts->env, &opts->nenv)) != 0 ||
            (r = deserialise_array(m,
            &opts->permitopen, &opts->npermitopen)) != 0 ||
            (r = deserialise_array(m,
            &opts->permitlisten, &opts->npermitlisten)) != 0)
                goto out;

        /* success */
        r = 0;
        *optsp = opts;
        opts = NULL;
 out:
        sshauthopt_free(opts);
        return r;
}