upstream: Introduce a new API for handling authorized_keys options.

This API parses options to a dedicated structure rather than the old API's
approach of setting global state. It also includes support for merging
options, e.g. from authorized_keys, authorized_principals and/or
certificates.

feedback and ok markus@

OpenBSD-Commit-ID: 98badda102cd575210d7802943e93a34232c80a2

2 files changed, 897 insertions, 2 deletions

diff --git a/auth-options.c b/auth-options.c
index bed00eef0..8b93b51e5 100644
--- a/auth-options.c
+++ b/auth-options.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-options.c,v 1.74 2017/09/12 06:32:07 djm Exp $ */
+/* $OpenBSD: auth-options.c,v 1.75 2018/03/03 03:06:02 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -9,6 +9,21 @@
  * incompatible with the protocol description in the RFC file, it must be
  * called by a name other than "ssh" or "Secure Shell".
  */
+/*
+ * 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"
 
@@ -19,6 +34,8 @@
 #include <string.h>
 #include <stdio.h>
 #include <stdarg.h>
+#include <ctype.h>
+#include <limits.h>
 
 #include "openbsd-compat/sys-queue.h"
 
@@ -27,6 +44,7 @@
 #include "xmalloc.h"
 #include "match.h"
 #include "ssherr.h"
+#include "ssh2.h"
 #include "log.h"
 #include "canohost.h"
 #include "packet.h"
@@ -661,3 +679,812 @@ auth_cert_options(struct sshkey *k, struct passwd *pw, const char **reason)
         return 0;
 }
 
+/*
+ * authorized_keys options processing.
+ */
+
+/*
+ * Match flag 'opt' in *optsp, and if allow_negate is set then also match
+ * 'no-opt'. Returns -1 if option not matched, 1 if option matches or 0
+ * if negated option matches.
+ * If the option or negated option matches, then *optsp is updated to
+ * point to the first character after the option.
+ */
+static int
+opt_flag(const char *opt, int allow_negate, const char **optsp)
+{
+        size_t opt_len = strlen(opt);
+        const char *opts = *optsp;
+        int negate = 0;
+
+        if (allow_negate && strncasecmp(opts, "no-", 3) == 0) {
+                opts += 3;
+                negate = 1;
+        }
+        if (strncasecmp(opts, opt, opt_len) == 0) {
+                *optsp = opts + opt_len;
+                return negate ? 0 : 1;
+        }
+        return -1;
+}
+
+static char *
+opt_dequote(const char **sp, const char **errstrp)
+{
+        const char *s = *sp;
+        char *ret;
+        size_t i;
+
+        *errstrp = NULL;
+        if (*s != '"') {
+                *errstrp = "missing start quote";
+                return NULL;
+        }
+        s++;
+        if ((ret = malloc(strlen((s)) + 1)) == NULL) {
+                *errstrp = "memory allocation failed";
+                return NULL;
+        }
+        for (i = 0; *s != '\0' && *s != '"';) {
+                if (s[0] == '\\' && s[1] == '"')
+                        s++;
+                ret[i++] = *s++;
+        }
+        if (*s == '\0') {
+                *errstrp = "missing end quote";
+                free(ret);
+                return NULL;
+        }
+        ret[i] = '\0';
+        s++;
+        *sp = s;
+        return ret;
+}
+
+static int
+opt_match(const char **opts, const char *term)
+{
+        if (strncasecmp((*opts), term, strlen(term)) == 0 &&
+            (*opts)[strlen(term)] == '=') {
+                *opts += strlen(term) + 1;
+                return 1;
+        }
+        return 0;
+}
+
+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 ((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("%s: sshbuf_fromb failed", __func__);
+                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("Unable to parse certificate options: %s",
+                            ssh_err(r));
+                        goto out;
+                }
+                debug3("found certificate option \"%.100s\" len %zu",
+                    name, sshbuf_len(data));
+                found = 0;
+                if ((which & OPTIONS_EXTENSIONS) != 0) {
+                        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, "force-command") == 0) {
+                                if ((r = sshbuf_get_cstring(data, &command,
+                                    NULL)) != 0) {
+                                        error("Unable to parse \"%s\" "
+                                            "section: %s", name, ssh_err(r));
+                                        goto out;
+                                }
+                                if (opts->force_command != NULL) {
+                                        error("Certificate has multiple "
+                                            "force-command options");
+                                        free(command);
+                                        goto out;
+                                }
+                                opts->force_command = command;
+                                found = 1;
+                        }
+                        if (strcmp(name, "source-address") == 0) {
+                                if ((r = sshbuf_get_cstring(data, &allowed,
+                                    NULL)) != 0) {
+                                        error("Unable to parse \"%s\" "
+                                            "section: %s", name, ssh_err(r));
+                                        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);
+
+        explicit_bzero(opts, sizeof(*opts));
+        free(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;
+}
+
+struct sshauthopt *
+sshauthopt_parse(const char *opts, const char **errstrp)
+{
+        char **oarray, *opt, *cp, *tmp, *host;
+        int r;
+        struct sshauthopt *ret = NULL;
+        const char *errstr = "unknown error";
+
+        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("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, "environment")) {
+                        if (ret->nenv > INT_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;
+                        }
+                        for (cp = opt; cp < tmp; cp++) {
+                                if (!isalnum((u_char)*cp)) {
+                                        free(opt);
+                                        errstr = "invalid environment string";
+                                        goto fail;
+                                }
+                        }
+                        /* Append it. */
+                        oarray = ret->env;
+                        if ((ret->env = recallocarray(ret->env, ret->nenv,
+                            ret->nenv + 1, sizeof(*ret->env))) == NULL) {
+                                free(opt);
+                                ret->env = oarray; /* put it back for cleanup */
+                                goto alloc_fail;
+                        }
+                        ret->env[ret->nenv++] = opt;
+                } else if (opt_match(&opts, "permitopen")) {
+                        if (ret->npermitopen > INT_MAX) {
+                                errstr = "too many permitopens";
+                                goto fail;
+                        }
+                        if ((opt = opt_dequote(&opts, &errstr)) == NULL)
+                                goto fail;
+                        if ((tmp = strdup(opt)) == NULL) {
+                                free(opt);
+                                goto alloc_fail;
+                        }
+                        cp = tmp;
+                        /* validate syntax of permitopen before recording it. */
+                        host = hpdelim(&cp);
+                        if (host == NULL || strlen(host) >= NI_MAXHOST) {
+                                free(tmp);
+                                free(opt);
+                                errstr = "invalid permitopen hostname";
+                                goto fail;
+                        }
+                        /*
+                         * 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);
+                                errstr = "invalid permitopen port";
+                                goto fail;
+                        }
+                        /* XXX - add streamlocal support */
+                        free(tmp);
+                        /* Record it */
+                        oarray = ret->permitopen;
+                        if ((ret->permitopen = recallocarray(ret->permitopen,
+                            ret->npermitopen, ret->npermitopen + 1,
+                            sizeof(*ret->permitopen))) == NULL) {
+                                free(opt);
+                                ret->permitopen = oarray;
+                                goto alloc_fail;
+                        }
+                        ret->permitopen[ret->npermitopen++] = opt;
+                } 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 and environment 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;
+        }
+
+        /* Flags are logical-AND (i.e. must be set in both for permission) */
+#define OPTFLAG(x) ret->x = (primary->x == 1) && (additional->x == 1)
+        OPTFLAG(permit_port_forwarding_flag);
+        OPTFLAG(permit_agent_forwarding_flag);
+        OPTFLAG(permit_x11_forwarding_flag);
+        OPTFLAG(permit_pty_flag);
+        OPTFLAG(permit_user_rc);
+#undef OPTFLAG
+
+        /*
+         * 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);
+#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) {
+                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;
+
+        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) {
+                        sshbuf_free(b);
+                        return r;
+                }
+        }
+        if ((r = sshbuf_put_u32(m, n)) != 0 ||
+            (r = sshbuf_put_stringb(m, b)) != 0) {
+                sshbuf_free(b);
+                return r;
+        }
+        /* success */
+        return 0;
+}
+
+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:
+        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)
+                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)
+                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;
+
+#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);
+#undef OPT_FLAG
+
+        /* 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)
+                goto out;
+
+        /* success */
+        r = 0;
+        *optsp = opts;
+        opts = NULL;
+ out:
+        sshauthopt_free(opts);
+        return r;
+}
diff --git a/auth-options.h b/auth-options.h
index 547f01635..0dbfc325e 100644
--- a/auth-options.h
+++ b/auth-options.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-options.h,v 1.23 2017/05/31 10:54:00 markus Exp $ */
+/* $OpenBSD: auth-options.h,v 1.24 2018/03/03 03:06:02 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -15,6 +15,9 @@
 #ifndef AUTH_OPTIONS_H
 #define AUTH_OPTIONS_H
 
+struct passwd;
+struct sshkey;
+
 /* Linked list of custom environment strings */
 struct envstring {
         struct envstring *next;
@@ -37,4 +40,69 @@ int	auth_parse_options(struct passwd *, char *, const char *, u_long);
 void    auth_clear_options(void);
 int     auth_cert_options(struct sshkey *, struct passwd *, const char **);
 
+/* authorized_keys options handling */
+
+/*
+ * sshauthopt represents key options parsed from authorized_keys or
+ * from certificate extensions/options.
+ */
+struct sshauthopt {
+        /* Feature flags */
+        int permit_port_forwarding_flag;
+        int permit_agent_forwarding_flag;
+        int permit_x11_forwarding_flag;
+        int permit_pty_flag;
+        int permit_user_rc;
+
+        /* "restrict" keyword was invoked */
+        int restricted;
+
+        /* Certificate-related options */
+        int cert_authority;
+        char *cert_principals;
+
+        int force_tun_device;
+        char *force_command;
+
+        /* Custom environment */
+        size_t nenv;
+        char **env;
+
+        /* Permitted port forwardings */
+        size_t npermitopen;
+        char **permitopen;
+
+        /*
+         * Permitted host/addresses (comma-separated)
+         * Caller must check source address matches both lists (if present).
+         */
+        char *required_from_host_cert;
+        char *required_from_host_keys;
+};
+
+struct sshauthopt *sshauthopt_new(void);
+struct sshauthopt *sshauthopt_new_with_keys_defaults(void);
+void sshauthopt_free(struct sshauthopt *opts);
+struct sshauthopt *sshauthopt_copy(const struct sshauthopt *orig);
+int sshauthopt_serialise(const struct sshauthopt *opts, struct sshbuf *m, int);
+int sshauthopt_deserialise(struct sshbuf *m, struct sshauthopt **opts);
+
+/*
+ * Parse authorized_keys options. Returns an options structure on success
+ * or NULL on failure. Will set errstr on failure.
+ */
+struct sshauthopt *sshauthopt_parse(const char *s, const char **errstr);
+
+/*
+ * Parse certification options to a struct sshauthopt.
+ * Returns options on success or NULL on failure.
+ */
+struct sshauthopt *sshauthopt_from_cert(struct sshkey *k);
+
+/*
+ * Merge key options.
+ */
+struct sshauthopt *sshauthopt_merge(const struct sshauthopt *primary,
+    const struct sshauthopt *additional, const char **errstrp);
+
 #endif