[openssh-commits] [openssh] 03/07: upstream: Introduce a new API for handling authorized_keys options.

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Sat Mar 3 14:39:56 AEDT 2018


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djm pushed a commit to branch master
in repository openssh.

commit 90c4bec8b5f9ec4c003ae4abdf13fc7766f00c8b
Author: djm at openbsd.org <djm at openbsd.org>
Date:   Sat Mar 3 03:06:02 2018 +0000

    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
---
 auth-options.c | 829 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 auth-options.h |  70 ++++-
 2 files changed, 897 insertions(+), 2 deletions(-)

diff --git a/auth-options.c b/auth-options.c
index bed00eef..8b93b51e 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 at cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo at 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 at 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 547f0163..0dbfc325 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 at 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

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