Adding upstream version 1:9.6p1.upstream/1%9.6p1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2468 insertions, 0 deletions

diff --git a/ssh-agent.c b/ssh-agent.c
new file mode 100644
index 0000000..b6a3f48
--- /dev/null
+++ b/ssh-agent.c
@@ -0,0 +1,2468 @@
+/* $OpenBSD: ssh-agent.c,v 1.303 2023/12/18 14:48:08 djm Exp $ */
+/*
+ * Author: Tatu Ylonen <ylo@cs.hut.fi>
+ * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ *                    All rights reserved
+ * The authentication agent program.
+ *
+ * As far as I am concerned, the code I have written for this software
+ * can be used freely for any purpose.  Any derived versions of this
+ * software must be clearly marked as such, and if the derived work is
+ * incompatible with the protocol description in the RFC file, it must be
+ * called by a name other than "ssh" or "Secure Shell".
+ *
+ * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+#include <sys/resource.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+#ifdef HAVE_SYS_TIME_H
+# include <sys/time.h>
+#endif
+#ifdef HAVE_SYS_UN_H
+# include <sys/un.h>
+#endif
+#include "openbsd-compat/sys-queue.h"
+
+#ifdef WITH_OPENSSL
+#include <openssl/evp.h>
+#include "openbsd-compat/openssl-compat.h"
+#endif
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#ifdef HAVE_PATHS_H
+# include <paths.h>
+#endif
+#ifdef HAVE_POLL_H
+# include <poll.h>
+#endif
+#include <signal.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <string.h>
+#include <unistd.h>
+#ifdef HAVE_UTIL_H
+# include <util.h>
+#endif
+
+#include "xmalloc.h"
+#include "ssh.h"
+#include "ssh2.h"
+#include "sshbuf.h"
+#include "sshkey.h"
+#include "authfd.h"
+#include "log.h"
+#include "misc.h"
+#include "digest.h"
+#include "ssherr.h"
+#include "match.h"
+#include "msg.h"
+#include "pathnames.h"
+#include "ssh-pkcs11.h"
+#include "sk-api.h"
+#include "myproposal.h"
+
+#ifndef DEFAULT_ALLOWED_PROVIDERS
+# define DEFAULT_ALLOWED_PROVIDERS "/usr/lib*/*,/usr/local/lib*/*"
+#endif
+
+/* Maximum accepted message length */
+#define AGENT_MAX_LEN		(256*1024)
+/* Maximum bytes to read from client socket */
+#define AGENT_RBUF_LEN		(4096)
+/* Maximum number of recorded session IDs/hostkeys per connection */
+#define AGENT_MAX_SESSION_IDS		16
+/* Maximum size of session ID */
+#define AGENT_MAX_SID_LEN		128
+/* Maximum number of destination constraints to accept on a key */
+#define AGENT_MAX_DEST_CONSTRAINTS	1024
+/* Maximum number of associated certificate constraints to accept on a key */
+#define AGENT_MAX_EXT_CERTS		1024
+
+/* XXX store hostkey_sid in a refcounted tree */
+
+typedef enum {
+	AUTH_UNUSED = 0,
+	AUTH_SOCKET = 1,
+	AUTH_CONNECTION = 2,
+} sock_type;
+
+struct hostkey_sid {
+	struct sshkey *key;
+	struct sshbuf *sid;
+	int forwarded;
+};
+
+typedef struct socket_entry {
+	int fd;
+	sock_type type;
+	struct sshbuf *input;
+	struct sshbuf *output;
+	struct sshbuf *request;
+	size_t nsession_ids;
+	struct hostkey_sid *session_ids;
+	int session_bind_attempted;
+} SocketEntry;
+
+u_int sockets_alloc = 0;
+SocketEntry *sockets = NULL;
+
+typedef struct identity {
+	TAILQ_ENTRY(identity) next;
+	struct sshkey *key;
+	char *comment;
+	char *provider;
+	time_t death;
+	u_int confirm;
+	char *sk_provider;
+	struct dest_constraint *dest_constraints;
+	size_t ndest_constraints;
+} Identity;
+
+struct idtable {
+	int nentries;
+	TAILQ_HEAD(idqueue, identity) idlist;
+};
+
+/* private key table */
+struct idtable *idtab;
+
+int max_fd = 0;
+
+/* pid of shell == parent of agent */
+pid_t parent_pid = -1;
+time_t parent_alive_interval = 0;
+
+/* pid of process for which cleanup_socket is applicable */
+pid_t cleanup_pid = 0;
+
+/* pathname and directory for AUTH_SOCKET */
+char socket_name[PATH_MAX];
+char socket_dir[PATH_MAX];
+
+/* Pattern-list of allowed PKCS#11/Security key paths */
+static char *allowed_providers;
+
+/*
+ * Allows PKCS11 providers or SK keys that use non-internal providers to
+ * be added over a remote connection (identified by session-bind@openssh.com).
+ */
+static int remote_add_provider;
+
+/* locking */
+#define LOCK_SIZE	32
+#define LOCK_SALT_SIZE	16
+#define LOCK_ROUNDS	1
+int locked = 0;
+u_char lock_pwhash[LOCK_SIZE];
+u_char lock_salt[LOCK_SALT_SIZE];
+
+extern char *__progname;
+
+/* Default lifetime in seconds (0 == forever) */
+static int lifetime = 0;
+
+static int fingerprint_hash = SSH_FP_HASH_DEFAULT;
+
+/* Refuse signing of non-SSH messages for web-origin FIDO keys */
+static int restrict_websafe = 1;
+
+static void
+close_socket(SocketEntry *e)
+{
+	size_t i;
+
+	close(e->fd);
+	sshbuf_free(e->input);
+	sshbuf_free(e->output);
+	sshbuf_free(e->request);
+	for (i = 0; i < e->nsession_ids; i++) {
+		sshkey_free(e->session_ids[i].key);
+		sshbuf_free(e->session_ids[i].sid);
+	}
+	free(e->session_ids);
+	memset(e, '\0', sizeof(*e));
+	e->fd = -1;
+	e->type = AUTH_UNUSED;
+}
+
+static void
+idtab_init(void)
+{
+	idtab = xcalloc(1, sizeof(*idtab));
+	TAILQ_INIT(&idtab->idlist);
+	idtab->nentries = 0;
+}
+
+static void
+free_dest_constraint_hop(struct dest_constraint_hop *dch)
+{
+	u_int i;
+
+	if (dch == NULL)
+		return;
+	free(dch->user);
+	free(dch->hostname);
+	for (i = 0; i < dch->nkeys; i++)
+		sshkey_free(dch->keys[i]);
+	free(dch->keys);
+	free(dch->key_is_ca);
+}
+
+static void
+free_dest_constraints(struct dest_constraint *dcs, size_t ndcs)
+{
+	size_t i;
+
+	for (i = 0; i < ndcs; i++) {
+		free_dest_constraint_hop(&dcs[i].from);
+		free_dest_constraint_hop(&dcs[i].to);
+	}
+	free(dcs);
+}
+
+static void
+dup_dest_constraint_hop(const struct dest_constraint_hop *dch,
+    struct dest_constraint_hop *out)
+{
+	u_int i;
+	int r;
+
+	out->user = dch->user == NULL ? NULL : xstrdup(dch->user);
+	out->hostname = dch->hostname == NULL ? NULL : xstrdup(dch->hostname);
+	out->is_ca = dch->is_ca;
+	out->nkeys = dch->nkeys;
+	out->keys = out->nkeys == 0 ? NULL :
+	    xcalloc(out->nkeys, sizeof(*out->keys));
+	out->key_is_ca = out->nkeys == 0 ? NULL :
+	    xcalloc(out->nkeys, sizeof(*out->key_is_ca));
+	for (i = 0; i < dch->nkeys; i++) {
+		if (dch->keys[i] != NULL &&
+		    (r = sshkey_from_private(dch->keys[i],
+		    &(out->keys[i]))) != 0)
+			fatal_fr(r, "copy key");
+		out->key_is_ca[i] = dch->key_is_ca[i];
+	}
+}
+
+static struct dest_constraint *
+dup_dest_constraints(const struct dest_constraint *dcs, size_t ndcs)
+{
+	size_t i;
+	struct dest_constraint *ret;
+
+	if (ndcs == 0)
+		return NULL;
+	ret = xcalloc(ndcs, sizeof(*ret));
+	for (i = 0; i < ndcs; i++) {
+		dup_dest_constraint_hop(&dcs[i].from, &ret[i].from);
+		dup_dest_constraint_hop(&dcs[i].to, &ret[i].to);
+	}
+	return ret;
+}
+
+#ifdef DEBUG_CONSTRAINTS
+static void
+dump_dest_constraint_hop(const struct dest_constraint_hop *dch)
+{
+	u_int i;
+	char *fp;
+
+	debug_f("user %s hostname %s is_ca %d nkeys %u",
+	    dch->user == NULL ? "(null)" : dch->user,
+	    dch->hostname == NULL ? "(null)" : dch->hostname,
+	    dch->is_ca, dch->nkeys);
+	for (i = 0; i < dch->nkeys; i++) {
+		fp = NULL;
+		if (dch->keys[i] != NULL &&
+		    (fp = sshkey_fingerprint(dch->keys[i],
+		    SSH_FP_HASH_DEFAULT, SSH_FP_DEFAULT)) == NULL)
+			fatal_f("fingerprint failed");
+		debug_f("key %u/%u: %s%s%s key_is_ca %d", i, dch->nkeys,
+		    dch->keys[i] == NULL ? "" : sshkey_ssh_name(dch->keys[i]),
+		    dch->keys[i] == NULL ? "" : " ",
+		    dch->keys[i] == NULL ? "none" : fp,
+		    dch->key_is_ca[i]);
+		free(fp);
+	}
+}
+#endif /* DEBUG_CONSTRAINTS */
+
+static void
+dump_dest_constraints(const char *context,
+    const struct dest_constraint *dcs, size_t ndcs)
+{
+#ifdef DEBUG_CONSTRAINTS
+	size_t i;
+
+	debug_f("%s: %zu constraints", context, ndcs);
+	for (i = 0; i < ndcs; i++) {
+		debug_f("constraint %zu / %zu: from: ", i, ndcs);
+		dump_dest_constraint_hop(&dcs[i].from);
+		debug_f("constraint %zu / %zu: to: ", i, ndcs);
+		dump_dest_constraint_hop(&dcs[i].to);
+	}
+	debug_f("done for %s", context);
+#endif /* DEBUG_CONSTRAINTS */
+}
+
+static void
+free_identity(Identity *id)
+{
+	sshkey_free(id->key);
+	free(id->provider);
+	free(id->comment);
+	free(id->sk_provider);
+	free_dest_constraints(id->dest_constraints, id->ndest_constraints);
+	free(id);
+}
+
+/*
+ * Match 'key' against the key/CA list in a destination constraint hop
+ * Returns 0 on success or -1 otherwise.
+ */
+static int
+match_key_hop(const char *tag, const struct sshkey *key,
+    const struct dest_constraint_hop *dch)
+{
+	const char *reason = NULL;
+	const char *hostname = dch->hostname ? dch->hostname : "(ORIGIN)";
+	u_int i;
+	char *fp;
+
+	if (key == NULL)
+		return -1;
+	/* XXX logspam */
+	if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
+	    SSH_FP_DEFAULT)) == NULL)
+		fatal_f("fingerprint failed");
+	debug3_f("%s: entering hostname %s, requested key %s %s, %u keys avail",
+	    tag, hostname, sshkey_type(key), fp, dch->nkeys);
+	free(fp);
+	for (i = 0; i < dch->nkeys; i++) {
+		if (dch->keys[i] == NULL)
+			return -1;
+		/* XXX logspam */
+		if ((fp = sshkey_fingerprint(dch->keys[i], SSH_FP_HASH_DEFAULT,
+		    SSH_FP_DEFAULT)) == NULL)
+			fatal_f("fingerprint failed");
+		debug3_f("%s: key %u: %s%s %s", tag, i,
+		    dch->key_is_ca[i] ? "CA " : "",
+		    sshkey_type(dch->keys[i]), fp);
+		free(fp);
+		if (!sshkey_is_cert(key)) {
+			/* plain key */
+			if (dch->key_is_ca[i] ||
+			    !sshkey_equal(key, dch->keys[i]))
+				continue;
+			return 0;
+		}
+		/* certificate */
+		if (!dch->key_is_ca[i])
+			continue;
+		if (key->cert == NULL || key->cert->signature_key == NULL)
+			return -1; /* shouldn't happen */
+		if (!sshkey_equal(key->cert->signature_key, dch->keys[i]))
+			continue;
+		if (sshkey_cert_check_host(key, hostname, 1,
+		    SSH_ALLOWED_CA_SIGALGS, &reason) != 0) {
+			debug_f("cert %s / hostname %s rejected: %s",
+			    key->cert->key_id, hostname, reason);
+			continue;
+		}
+		return 0;
+	}
+	return -1;
+}
+
+/* Check destination constraints on an identity against the hostkey/user */
+static int
+permitted_by_dest_constraints(const struct sshkey *fromkey,
+    const struct sshkey *tokey, Identity *id, const char *user,
+    const char **hostnamep)
+{
+	size_t i;
+	struct dest_constraint *d;
+
+	if (hostnamep != NULL)
+		*hostnamep = NULL;
+	for (i = 0; i < id->ndest_constraints; i++) {
+		d = id->dest_constraints + i;
+		/* XXX remove logspam */
+		debug2_f("constraint %zu %s%s%s (%u keys) > %s%s%s (%u keys)",
+		    i, d->from.user ? d->from.user : "",
+		    d->from.user ? "@" : "",
+		    d->from.hostname ? d->from.hostname : "(ORIGIN)",
+		    d->from.nkeys,
+		    d->to.user ? d->to.user : "", d->to.user ? "@" : "",
+		    d->to.hostname ? d->to.hostname : "(ANY)", d->to.nkeys);
+
+		/* Match 'from' key */
+		if (fromkey == NULL) {
+			/* We are matching the first hop */
+			if (d->from.hostname != NULL || d->from.nkeys != 0)
+				continue;
+		} else if (match_key_hop("from", fromkey, &d->from) != 0)
+			continue;
+
+		/* Match 'to' key */
+		if (tokey != NULL && match_key_hop("to", tokey, &d->to) != 0)
+			continue;
+
+		/* Match user if specified */
+		if (d->to.user != NULL && user != NULL &&
+		    !match_pattern(user, d->to.user))
+			continue;
+
+		/* successfully matched this constraint */
+		if (hostnamep != NULL)
+			*hostnamep = d->to.hostname;
+		debug2_f("allowed for hostname %s",
+		    d->to.hostname == NULL ? "*" : d->to.hostname);
+		return 0;
+	}
+	/* no match */
+	debug2_f("%s identity \"%s\" not permitted for this destination",
+	    sshkey_type(id->key), id->comment);
+	return -1;
+}
+
+/*
+ * Check whether hostkeys on a SocketEntry and the optionally specified user
+ * are permitted by the destination constraints on the Identity.
+ * Returns 0 on success or -1 otherwise.
+ */
+static int
+identity_permitted(Identity *id, SocketEntry *e, char *user,
+    const char **forward_hostnamep, const char **last_hostnamep)
+{
+	size_t i;
+	const char **hp;
+	struct hostkey_sid *hks;
+	const struct sshkey *fromkey = NULL;
+	const char *test_user;
+	char *fp1, *fp2;
+
+	/* XXX remove logspam */
+	debug3_f("entering: key %s comment \"%s\", %zu socket bindings, "
+	    "%zu constraints", sshkey_type(id->key), id->comment,
+	    e->nsession_ids, id->ndest_constraints);
+	if (id->ndest_constraints == 0)
+		return 0; /* unconstrained */
+	if (e->session_bind_attempted && e->nsession_ids == 0) {
+		error_f("previous session bind failed on socket");
+		return -1;
+	}
+	if (e->nsession_ids == 0)
+		return 0; /* local use */
+	/*
+	 * Walk through the hops recorded by session_id and try to find a
+	 * constraint that satisfies each.
+	 */
+	for (i = 0; i < e->nsession_ids; i++) {
+		hks = e->session_ids + i;
+		if (hks->key == NULL)
+			fatal_f("internal error: no bound key");
+		/* XXX remove logspam */
+		fp1 = fp2 = NULL;
+		if (fromkey != NULL &&
+		    (fp1 = sshkey_fingerprint(fromkey, SSH_FP_HASH_DEFAULT,
+		    SSH_FP_DEFAULT)) == NULL)
+			fatal_f("fingerprint failed");
+		if ((fp2 = sshkey_fingerprint(hks->key, SSH_FP_HASH_DEFAULT,
+		    SSH_FP_DEFAULT)) == NULL)
+			fatal_f("fingerprint failed");
+		debug3_f("socketentry fd=%d, entry %zu %s, "
+		    "from hostkey %s %s to user %s hostkey %s %s",
+		    e->fd, i, hks->forwarded ? "FORWARD" : "AUTH",
+		    fromkey ? sshkey_type(fromkey) : "(ORIGIN)",
+		    fromkey ? fp1 : "", user ? user : "(ANY)",
+		    sshkey_type(hks->key), fp2);
+		free(fp1);
+		free(fp2);
+		/*
+		 * Record the hostnames for the initial forwarding and
+		 * the final destination.
+		 */
+		hp = NULL;
+		if (i == e->nsession_ids - 1)
+			hp = last_hostnamep;
+		else if (i == 0)
+			hp = forward_hostnamep;
+		/* Special handling for final recorded binding */
+		test_user = NULL;
+		if (i == e->nsession_ids - 1) {
+			/* Can only check user at final hop */
+			test_user = user;
+			/*
+			 * user is only presented for signature requests.
+			 * If this is the case, make sure last binding is not
+			 * for a forwarding.
+			 */
+			if (hks->forwarded && user != NULL) {
+				error_f("tried to sign on forwarding hop");
+				return -1;
+			}
+		} else if (!hks->forwarded) {
+			error_f("tried to forward though signing bind");
+			return -1;
+		}
+		if (permitted_by_dest_constraints(fromkey, hks->key, id,
+		    test_user, hp) != 0)
+			return -1;
+		fromkey = hks->key;
+	}
+	/*
+	 * Another special case: if the last bound session ID was for a
+	 * forwarding, and this function is not being called to check a sign
+	 * request (i.e. no 'user' supplied), then only permit the key if
+	 * there is a permission that would allow it to be used at another
+	 * destination. This hides keys that are allowed to be used to
+	 * authenticate *to* a host but not permitted for *use* beyond it.
+	 */
+	hks = &e->session_ids[e->nsession_ids - 1];
+	if (hks->forwarded && user == NULL &&
+	    permitted_by_dest_constraints(hks->key, NULL, id,
+	    NULL, NULL) != 0) {
+		debug3_f("key permitted at host but not after");
+		return -1;
+	}
+
+	/* success */
+	return 0;
+}
+
+static int
+socket_is_remote(SocketEntry *e)
+{
+	return e->session_bind_attempted || (e->nsession_ids != 0);
+}
+
+/* return matching private key for given public key */
+static Identity *
+lookup_identity(struct sshkey *key)
+{
+	Identity *id;
+
+	TAILQ_FOREACH(id, &idtab->idlist, next) {
+		if (sshkey_equal(key, id->key))
+			return (id);
+	}
+	return (NULL);
+}
+
+/* Check confirmation of keysign request */
+static int
+confirm_key(Identity *id, const char *extra)
+{
+	char *p;
+	int ret = -1;
+
+	p = sshkey_fingerprint(id->key, fingerprint_hash, SSH_FP_DEFAULT);
+	if (p != NULL &&
+	    ask_permission("Allow use of key %s?\nKey fingerprint %s.%s%s",
+	    id->comment, p,
+	    extra == NULL ? "" : "\n", extra == NULL ? "" : extra))
+		ret = 0;
+	free(p);
+
+	return (ret);
+}
+
+static void
+send_status(SocketEntry *e, int success)
+{
+	int r;
+
+	if ((r = sshbuf_put_u32(e->output, 1)) != 0 ||
+	    (r = sshbuf_put_u8(e->output, success ?
+	    SSH_AGENT_SUCCESS : SSH_AGENT_FAILURE)) != 0)
+		fatal_fr(r, "compose");
+}
+
+/* send list of supported public keys to 'client' */
+static void
+process_request_identities(SocketEntry *e)
+{
+	Identity *id;
+	struct sshbuf *msg, *keys;
+	int r;
+	u_int i = 0, nentries = 0;
+	char *fp;
+
+	debug2_f("entering");
+
+	if ((msg = sshbuf_new()) == NULL || (keys = sshbuf_new()) == NULL)
+		fatal_f("sshbuf_new failed");
+	TAILQ_FOREACH(id, &idtab->idlist, next) {
+		if ((fp = sshkey_fingerprint(id->key, SSH_FP_HASH_DEFAULT,
+		    SSH_FP_DEFAULT)) == NULL)
+			fatal_f("fingerprint failed");
+		debug_f("key %u / %u: %s %s", i++, idtab->nentries,
+		    sshkey_ssh_name(id->key), fp);
+		dump_dest_constraints(__func__,
+		    id->dest_constraints, id->ndest_constraints);
+		free(fp);
+		/* identity not visible, don't include in response */
+		if (identity_permitted(id, e, NULL, NULL, NULL) != 0)
+			continue;
+		if ((r = sshkey_puts_opts(id->key, keys,
+		    SSHKEY_SERIALIZE_INFO)) != 0 ||
+		    (r = sshbuf_put_cstring(keys, id->comment)) != 0) {
+			error_fr(r, "compose key/comment");
+			continue;
+		}
+		nentries++;
+	}
+	debug2_f("replying with %u allowed of %u available keys",
+	    nentries, idtab->nentries);
+	if ((r = sshbuf_put_u8(msg, SSH2_AGENT_IDENTITIES_ANSWER)) != 0 ||
+	    (r = sshbuf_put_u32(msg, nentries)) != 0 ||
+	    (r = sshbuf_putb(msg, keys)) != 0)
+		fatal_fr(r, "compose");
+	if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
+		fatal_fr(r, "enqueue");
+	sshbuf_free(msg);
+	sshbuf_free(keys);
+}
+
+
+static char *
+agent_decode_alg(struct sshkey *key, u_int flags)
+{
+	if (key->type == KEY_RSA) {
+		if (flags & SSH_AGENT_RSA_SHA2_256)
+			return "rsa-sha2-256";
+		else if (flags & SSH_AGENT_RSA_SHA2_512)
+			return "rsa-sha2-512";
+	} else if (key->type == KEY_RSA_CERT) {
+		if (flags & SSH_AGENT_RSA_SHA2_256)
+			return "rsa-sha2-256-cert-v01@openssh.com";
+		else if (flags & SSH_AGENT_RSA_SHA2_512)
+			return "rsa-sha2-512-cert-v01@openssh.com";
+	}
+	return NULL;
+}
+
+/*
+ * Attempt to parse the contents of a buffer as a SSH publickey userauth
+ * request, checking its contents for consistency and matching the embedded
+ * key against the one that is being used for signing.
+ * Note: does not modify msg buffer.
+ * Optionally extract the username, session ID and/or hostkey from the request.
+ */
+static int
+parse_userauth_request(struct sshbuf *msg, const struct sshkey *expected_key,
+    char **userp, struct sshbuf **sess_idp, struct sshkey **hostkeyp)
+{
+	struct sshbuf *b = NULL, *sess_id = NULL;
+	char *user = NULL, *service = NULL, *method = NULL, *pkalg = NULL;
+	int r;
+	u_char t, sig_follows;
+	struct sshkey *mkey = NULL, *hostkey = NULL;
+
+	if (userp != NULL)
+		*userp = NULL;
+	if (sess_idp != NULL)
+		*sess_idp = NULL;
+	if (hostkeyp != NULL)
+		*hostkeyp = NULL;
+	if ((b = sshbuf_fromb(msg)) == NULL)
+		fatal_f("sshbuf_fromb");
+
+	/* SSH userauth request */
+	if ((r = sshbuf_froms(b, &sess_id)) != 0)
+		goto out;
+	if (sshbuf_len(sess_id) == 0) {
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	if ((r = sshbuf_get_u8(b, &t)) != 0 || /* SSH2_MSG_USERAUTH_REQUEST */
+	    (r = sshbuf_get_cstring(b, &user, NULL)) != 0 || /* server user */
+	    (r = sshbuf_get_cstring(b, &service, NULL)) != 0 || /* service */
+	    (r = sshbuf_get_cstring(b, &method, NULL)) != 0 || /* method */
+	    (r = sshbuf_get_u8(b, &sig_follows)) != 0 || /* sig-follows */
+	    (r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || /* alg */
+	    (r = sshkey_froms(b, &mkey)) != 0) /* key */
+		goto out;
+	if (t != SSH2_MSG_USERAUTH_REQUEST ||
+	    sig_follows != 1 ||
+	    strcmp(service, "ssh-connection") != 0 ||
+	    !sshkey_equal(expected_key, mkey) ||
+	    sshkey_type_from_name(pkalg) != expected_key->type) {
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	if (strcmp(method, "publickey-hostbound-v00@openssh.com") == 0) {
+		if ((r = sshkey_froms(b, &hostkey)) != 0)
+			goto out;
+	} else if (strcmp(method, "publickey") != 0) {
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	if (sshbuf_len(b) != 0) {
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	/* success */
+	r = 0;
+	debug3_f("well formed userauth");
+	if (userp != NULL) {
+		*userp = user;
+		user = NULL;
+	}
+	if (sess_idp != NULL) {
+		*sess_idp = sess_id;
+		sess_id = NULL;
+	}
+	if (hostkeyp != NULL) {
+		*hostkeyp = hostkey;
+		hostkey = NULL;
+	}
+ out:
+	sshbuf_free(b);
+	sshbuf_free(sess_id);
+	free(user);
+	free(service);
+	free(method);
+	free(pkalg);
+	sshkey_free(mkey);
+	sshkey_free(hostkey);
+	return r;
+}
+
+/*
+ * Attempt to parse the contents of a buffer as a SSHSIG signature request.
+ * Note: does not modify buffer.
+ */
+static int
+parse_sshsig_request(struct sshbuf *msg)
+{
+	int r;
+	struct sshbuf *b;
+
+	if ((b = sshbuf_fromb(msg)) == NULL)
+		fatal_f("sshbuf_fromb");
+
+	if ((r = sshbuf_cmp(b, 0, "SSHSIG", 6)) != 0 ||
+	    (r = sshbuf_consume(b, 6)) != 0 ||
+	    (r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* namespace */
+	    (r = sshbuf_get_string_direct(b, NULL, NULL)) != 0 || /* reserved */
+	    (r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* hashalg */
+	    (r = sshbuf_get_string_direct(b, NULL, NULL)) != 0) /* H(msg) */
+		goto out;
+	if (sshbuf_len(b) != 0) {
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	/* success */
+	r = 0;
+ out:
+	sshbuf_free(b);
+	return r;
+}
+
+/*
+ * This function inspects a message to be signed by a FIDO key that has a
+ * web-like application string (i.e. one that does not begin with "ssh:".
+ * It checks that the message is one of those expected for SSH operations
+ * (pubkey userauth, sshsig, CA key signing) to exclude signing challenges
+ * for the web.
+ */
+static int
+check_websafe_message_contents(struct sshkey *key, struct sshbuf *data)
+{
+	if (parse_userauth_request(data, key, NULL, NULL, NULL) == 0) {
+		debug_f("signed data matches public key userauth request");
+		return 1;
+	}
+	if (parse_sshsig_request(data) == 0) {
+		debug_f("signed data matches SSHSIG signature request");
+		return 1;
+	}
+
+	/* XXX check CA signature operation */
+
+	error("web-origin key attempting to sign non-SSH message");
+	return 0;
+}
+
+static int
+buf_equal(const struct sshbuf *a, const struct sshbuf *b)
+{
+	if (sshbuf_ptr(a) == NULL || sshbuf_ptr(b) == NULL)
+		return SSH_ERR_INVALID_ARGUMENT;
+	if (sshbuf_len(a) != sshbuf_len(b))
+		return SSH_ERR_INVALID_FORMAT;
+	if (timingsafe_bcmp(sshbuf_ptr(a), sshbuf_ptr(b), sshbuf_len(a)) != 0)
+		return SSH_ERR_INVALID_FORMAT;
+	return 0;
+}
+
+/* ssh2 only */
+static void
+process_sign_request2(SocketEntry *e)
+{
+	u_char *signature = NULL;
+	size_t slen = 0;
+	u_int compat = 0, flags;
+	int r, ok = -1, retried = 0;
+	char *fp = NULL, *pin = NULL, *prompt = NULL;
+	char *user = NULL, *sig_dest = NULL;
+	const char *fwd_host = NULL, *dest_host = NULL;
+	struct sshbuf *msg = NULL, *data = NULL, *sid = NULL;
+	struct sshkey *key = NULL, *hostkey = NULL;
+	struct identity *id;
+	struct notifier_ctx *notifier = NULL;
+
+	debug_f("entering");
+
+	if ((msg = sshbuf_new()) == NULL || (data = sshbuf_new()) == NULL)
+		fatal_f("sshbuf_new failed");
+	if ((r = sshkey_froms(e->request, &key)) != 0 ||
+	    (r = sshbuf_get_stringb(e->request, data)) != 0 ||
+	    (r = sshbuf_get_u32(e->request, &flags)) != 0) {
+		error_fr(r, "parse");
+		goto send;
+	}
+
+	if ((id = lookup_identity(key)) == NULL) {
+		verbose_f("%s key not found", sshkey_type(key));
+		goto send;
+	}
+	if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
+	    SSH_FP_DEFAULT)) == NULL)
+		fatal_f("fingerprint failed");
+
+	if (id->ndest_constraints != 0) {
+		if (e->nsession_ids == 0) {
+			logit_f("refusing use of destination-constrained key "
+			    "to sign on unbound connection");
+			goto send;
+		}
+		if (parse_userauth_request(data, key, &user, &sid,
+		    &hostkey) != 0) {
+			logit_f("refusing use of destination-constrained key "
+			   "to sign an unidentified signature");
+			goto send;
+		}
+		/* XXX logspam */
+		debug_f("user=%s", user);
+		if (identity_permitted(id, e, user, &fwd_host, &dest_host) != 0)
+			goto send;
+		/* XXX display fwd_host/dest_host in askpass UI */
+		/*
+		 * Ensure that the session ID is the most recent one
+		 * registered on the socket - it should have been bound by
+		 * ssh immediately before userauth.
+		 */
+		if (buf_equal(sid,
+		    e->session_ids[e->nsession_ids - 1].sid) != 0) {
+			error_f("unexpected session ID (%zu listed) on "
+			    "signature request for target user %s with "
+			    "key %s %s", e->nsession_ids, user,
+			    sshkey_type(id->key), fp);
+			goto send;
+		}
+		/*
+		 * Ensure that the hostkey embedded in the signature matches
+		 * the one most recently bound to the socket. An exception is
+		 * made for the initial forwarding hop.
+		 */
+		if (e->nsession_ids > 1 && hostkey == NULL) {
+			error_f("refusing use of destination-constrained key: "
+			    "no hostkey recorded in signature for forwarded "
+			    "connection");
+			goto send;
+		}
+		if (hostkey != NULL && !sshkey_equal(hostkey,
+		    e->session_ids[e->nsession_ids - 1].key)) {
+			error_f("refusing use of destination-constrained key: "
+			    "mismatch between hostkey in request and most "
+			    "recently bound session");
+			goto send;
+		}
+		xasprintf(&sig_dest, "public key authentication request for "
+		    "user \"%s\" to listed host", user);
+	}
+	if (id->confirm && confirm_key(id, sig_dest) != 0) {
+		verbose_f("user refused key");
+		goto send;
+	}
+	if (sshkey_is_sk(id->key)) {
+		if (restrict_websafe &&
+		    strncmp(id->key->sk_application, "ssh:", 4) != 0 &&
+		    !check_websafe_message_contents(key, data)) {
+			/* error already logged */
+			goto send;
+		}
+		if (id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD) {
+			notifier = notify_start(0,
+			    "Confirm user presence for key %s %s%s%s",
+			    sshkey_type(id->key), fp,
+			    sig_dest == NULL ? "" : "\n",
+			    sig_dest == NULL ? "" : sig_dest);
+		}
+	}
+ retry_pin:
+	if ((r = sshkey_sign(id->key, &signature, &slen,
+	    sshbuf_ptr(data), sshbuf_len(data), agent_decode_alg(key, flags),
+	    id->sk_provider, pin, compat)) != 0) {
+		debug_fr(r, "sshkey_sign");
+		if (pin == NULL && !retried && sshkey_is_sk(id->key) &&
+		    r == SSH_ERR_KEY_WRONG_PASSPHRASE) {
+			notify_complete(notifier, NULL);
+			notifier = NULL;
+			/* XXX include sig_dest */
+			xasprintf(&prompt, "Enter PIN%sfor %s key %s: ",
+			    (id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD) ?
+			    " and confirm user presence " : " ",
+			    sshkey_type(id->key), fp);
+			pin = read_passphrase(prompt, RP_USE_ASKPASS);
+			retried = 1;
+			goto retry_pin;
+		}
+		error_fr(r, "sshkey_sign");
+		goto send;
+	}
+	/* Success */
+	ok = 0;
+	debug_f("good signature");
+ send:
+	notify_complete(notifier, "User presence confirmed");
+
+	if (ok == 0) {
+		if ((r = sshbuf_put_u8(msg, SSH2_AGENT_SIGN_RESPONSE)) != 0 ||
+		    (r = sshbuf_put_string(msg, signature, slen)) != 0)
+			fatal_fr(r, "compose");
+	} else if ((r = sshbuf_put_u8(msg, SSH_AGENT_FAILURE)) != 0)
+		fatal_fr(r, "compose failure");
+
+	if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
+		fatal_fr(r, "enqueue");
+
+	sshbuf_free(sid);
+	sshbuf_free(data);
+	sshbuf_free(msg);
+	sshkey_free(key);
+	sshkey_free(hostkey);
+	free(fp);
+	free(signature);
+	free(sig_dest);
+	free(user);
+	free(prompt);
+	if (pin != NULL)
+		freezero(pin, strlen(pin));
+}
+
+/* shared */
+static void
+process_remove_identity(SocketEntry *e)
+{
+	int r, success = 0;
+	struct sshkey *key = NULL;
+	Identity *id;
+
+	debug2_f("entering");
+	if ((r = sshkey_froms(e->request, &key)) != 0) {
+		error_fr(r, "parse key");
+		goto done;
+	}
+	if ((id = lookup_identity(key)) == NULL) {
+		debug_f("key not found");
+		goto done;
+	}
+	/* identity not visible, cannot be removed */
+	if (identity_permitted(id, e, NULL, NULL, NULL) != 0)
+		goto done; /* error already logged */
+	/* We have this key, free it. */
+	if (idtab->nentries < 1)
+		fatal_f("internal error: nentries %d", idtab->nentries);
+	TAILQ_REMOVE(&idtab->idlist, id, next);
+	free_identity(id);
+	idtab->nentries--;
+	success = 1;
+ done:
+	sshkey_free(key);
+	send_status(e, success);
+}
+
+static void
+process_remove_all_identities(SocketEntry *e)
+{
+	Identity *id;
+
+	debug2_f("entering");
+	/* Loop over all identities and clear the keys. */
+	for (id = TAILQ_FIRST(&idtab->idlist); id;
+	    id = TAILQ_FIRST(&idtab->idlist)) {
+		TAILQ_REMOVE(&idtab->idlist, id, next);
+		free_identity(id);
+	}
+
+	/* Mark that there are no identities. */
+	idtab->nentries = 0;
+
+	/* Send success. */
+	send_status(e, 1);
+}
+
+/* removes expired keys and returns number of seconds until the next expiry */
+static time_t
+reaper(void)
+{
+	time_t deadline = 0, now = monotime();
+	Identity *id, *nxt;
+
+	for (id = TAILQ_FIRST(&idtab->idlist); id; id = nxt) {
+		nxt = TAILQ_NEXT(id, next);
+		if (id->death == 0)
+			continue;
+		if (now >= id->death) {
+			debug("expiring key '%s'", id->comment);
+			TAILQ_REMOVE(&idtab->idlist, id, next);
+			free_identity(id);
+			idtab->nentries--;
+		} else
+			deadline = (deadline == 0) ? id->death :
+			    MINIMUM(deadline, id->death);
+	}
+	if (deadline == 0 || deadline <= now)
+		return 0;
+	else
+		return (deadline - now);
+}
+
+static int
+parse_dest_constraint_hop(struct sshbuf *b, struct dest_constraint_hop *dch)
+{
+	u_char key_is_ca;
+	size_t elen = 0;
+	int r;
+	struct sshkey *k = NULL;
+	char *fp;
+
+	memset(dch, '\0', sizeof(*dch));
+	if ((r = sshbuf_get_cstring(b, &dch->user, NULL)) != 0 ||
+	    (r = sshbuf_get_cstring(b, &dch->hostname, NULL)) != 0 ||
+	    (r = sshbuf_get_string_direct(b, NULL, &elen)) != 0) {
+		error_fr(r, "parse");
+		goto out;
+	}
+	if (elen != 0) {
+		error_f("unsupported extensions (len %zu)", elen);
+		r = SSH_ERR_FEATURE_UNSUPPORTED;
+		goto out;
+	}
+	if (*dch->hostname == '\0') {
+		free(dch->hostname);
+		dch->hostname = NULL;
+	}
+	if (*dch->user == '\0') {
+		free(dch->user);
+		dch->user = NULL;
+	}
+	while (sshbuf_len(b) != 0) {
+		dch->keys = xrecallocarray(dch->keys, dch->nkeys,
+		    dch->nkeys + 1, sizeof(*dch->keys));
+		dch->key_is_ca = xrecallocarray(dch->key_is_ca, dch->nkeys,
+		    dch->nkeys + 1, sizeof(*dch->key_is_ca));
+		if ((r = sshkey_froms(b, &k)) != 0 ||
+		    (r = sshbuf_get_u8(b, &key_is_ca)) != 0)
+			goto out;
+		if ((fp = sshkey_fingerprint(k, SSH_FP_HASH_DEFAULT,
+		    SSH_FP_DEFAULT)) == NULL)
+			fatal_f("fingerprint failed");
+		debug3_f("%s%s%s: adding %skey %s %s",
+		    dch->user == NULL ? "" : dch->user,
+		    dch->user == NULL ? "" : "@",
+		    dch->hostname, key_is_ca ? "CA " : "", sshkey_type(k), fp);
+		free(fp);
+		dch->keys[dch->nkeys] = k;
+		dch->key_is_ca[dch->nkeys] = key_is_ca != 0;
+		dch->nkeys++;
+		k = NULL; /* transferred */
+	}
+	/* success */
+	r = 0;
+ out:
+	sshkey_free(k);
+	return r;
+}
+
+static int
+parse_dest_constraint(struct sshbuf *m, struct dest_constraint *dc)
+{
+	struct sshbuf *b = NULL, *frombuf = NULL, *tobuf = NULL;
+	int r;
+	size_t elen = 0;
+
+	debug3_f("entering");
+
+	memset(dc, '\0', sizeof(*dc));
+	if ((r = sshbuf_froms(m, &b)) != 0 ||
+	    (r = sshbuf_froms(b, &frombuf)) != 0 ||
+	    (r = sshbuf_froms(b, &tobuf)) != 0 ||
+	    (r = sshbuf_get_string_direct(b, NULL, &elen)) != 0) {
+		error_fr(r, "parse");
+		goto out;
+	}
+	if ((r = parse_dest_constraint_hop(frombuf, &dc->from)) != 0 ||
+	    (r = parse_dest_constraint_hop(tobuf, &dc->to)) != 0)
+		goto out; /* already logged */
+	if (elen != 0) {
+		error_f("unsupported extensions (len %zu)", elen);
+		r = SSH_ERR_FEATURE_UNSUPPORTED;
+		goto out;
+	}
+	debug2_f("parsed %s (%u keys) > %s%s%s (%u keys)",
+	    dc->from.hostname ? dc->from.hostname : "(ORIGIN)", dc->from.nkeys,
+	    dc->to.user ? dc->to.user : "", dc->to.user ? "@" : "",
+	    dc->to.hostname ? dc->to.hostname : "(ANY)", dc->to.nkeys);
+	/* check consistency */
+	if ((dc->from.hostname == NULL) != (dc->from.nkeys == 0) ||
+	    dc->from.user != NULL) {
+		error_f("inconsistent \"from\" specification");
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	if (dc->to.hostname == NULL || dc->to.nkeys == 0) {
+		error_f("incomplete \"to\" specification");
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	/* success */
+	r = 0;
+ out:
+	sshbuf_free(b);
+	sshbuf_free(frombuf);
+	sshbuf_free(tobuf);
+	return r;
+}
+
+static int
+parse_key_constraint_extension(struct sshbuf *m, char **sk_providerp,
+    struct dest_constraint **dcsp, size_t *ndcsp, int *cert_onlyp,
+    struct sshkey ***certs, size_t *ncerts)
+{
+	char *ext_name = NULL;
+	int r;
+	struct sshbuf *b = NULL;
+	u_char v;
+	struct sshkey *k;
+
+	if ((r = sshbuf_get_cstring(m, &ext_name, NULL)) != 0) {
+		error_fr(r, "parse constraint extension");
+		goto out;
+	}
+	debug_f("constraint ext %s", ext_name);
+	if (strcmp(ext_name, "sk-provider@openssh.com") == 0) {
+		if (sk_providerp == NULL) {
+			error_f("%s not valid here", ext_name);
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+		if (*sk_providerp != NULL) {
+			error_f("%s already set", ext_name);
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+		if ((r = sshbuf_get_cstring(m, sk_providerp, NULL)) != 0) {
+			error_fr(r, "parse %s", ext_name);
+			goto out;
+		}
+	} else if (strcmp(ext_name,
+	    "restrict-destination-v00@openssh.com") == 0) {
+		if (*dcsp != NULL) {
+			error_f("%s already set", ext_name);
+			goto out;
+		}
+		if ((r = sshbuf_froms(m, &b)) != 0) {
+			error_fr(r, "parse %s outer", ext_name);
+			goto out;
+		}
+		while (sshbuf_len(b) != 0) {
+			if (*ndcsp >= AGENT_MAX_DEST_CONSTRAINTS) {
+				error_f("too many %s constraints", ext_name);
+				goto out;
+			}
+			*dcsp = xrecallocarray(*dcsp, *ndcsp, *ndcsp + 1,
+			    sizeof(**dcsp));
+			if ((r = parse_dest_constraint(b,
+			    *dcsp + (*ndcsp)++)) != 0)
+				goto out; /* error already logged */
+		}
+	} else if (strcmp(ext_name,
+	    "associated-certs-v00@openssh.com") == 0) {
+		if (certs == NULL || ncerts == NULL || cert_onlyp == NULL) {
+			error_f("%s not valid here", ext_name);
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+		if (*certs != NULL) {
+			error_f("%s already set", ext_name);
+			goto out;
+		}
+		if ((r = sshbuf_get_u8(m, &v)) != 0 ||
+		    (r = sshbuf_froms(m, &b)) != 0) {
+			error_fr(r, "parse %s", ext_name);
+			goto out;
+		}
+		*cert_onlyp = v != 0;
+		while (sshbuf_len(b) != 0) {
+			if (*ncerts >= AGENT_MAX_EXT_CERTS) {
+				error_f("too many %s constraints", ext_name);
+				goto out;
+			}
+			*certs = xrecallocarray(*certs, *ncerts, *ncerts + 1,
+			    sizeof(**certs));
+			if ((r = sshkey_froms(b, &k)) != 0) {
+				error_fr(r, "parse key");
+				goto out;
+			}
+			(*certs)[(*ncerts)++] = k;
+		}
+	} else {
+		error_f("unsupported constraint \"%s\"", ext_name);
+		r = SSH_ERR_FEATURE_UNSUPPORTED;
+		goto out;
+	}
+	/* success */
+	r = 0;
+ out:
+	free(ext_name);
+	sshbuf_free(b);
+	return r;
+}
+
+static int
+parse_key_constraints(struct sshbuf *m, struct sshkey *k, time_t *deathp,
+    u_int *secondsp, int *confirmp, char **sk_providerp,
+    struct dest_constraint **dcsp, size_t *ndcsp,
+    int *cert_onlyp, size_t *ncerts, struct sshkey ***certs)
+{
+	u_char ctype;
+	int r;
+	u_int seconds, maxsign = 0;
+
+	while (sshbuf_len(m)) {
+		if ((r = sshbuf_get_u8(m, &ctype)) != 0) {
+			error_fr(r, "parse constraint type");
+			goto out;
+		}
+		switch (ctype) {
+		case SSH_AGENT_CONSTRAIN_LIFETIME:
+			if (*deathp != 0) {
+				error_f("lifetime already set");
+				r = SSH_ERR_INVALID_FORMAT;
+				goto out;
+			}
+			if ((r = sshbuf_get_u32(m, &seconds)) != 0) {
+				error_fr(r, "parse lifetime constraint");
+				goto out;
+			}
+			*deathp = monotime() + seconds;
+			*secondsp = seconds;
+			break;
+		case SSH_AGENT_CONSTRAIN_CONFIRM:
+			if (*confirmp != 0) {
+				error_f("confirm already set");
+				r = SSH_ERR_INVALID_FORMAT;
+				goto out;
+			}
+			*confirmp = 1;
+			break;
+		case SSH_AGENT_CONSTRAIN_MAXSIGN:
+			if (k == NULL) {
+				error_f("maxsign not valid here");
+				r = SSH_ERR_INVALID_FORMAT;
+				goto out;
+			}
+			if (maxsign != 0) {
+				error_f("maxsign already set");
+				r = SSH_ERR_INVALID_FORMAT;
+				goto out;
+			}
+			if ((r = sshbuf_get_u32(m, &maxsign)) != 0) {
+				error_fr(r, "parse maxsign constraint");
+				goto out;
+			}
+			if ((r = sshkey_enable_maxsign(k, maxsign)) != 0) {
+				error_fr(r, "enable maxsign");
+				goto out;
+			}
+			break;
+		case SSH_AGENT_CONSTRAIN_EXTENSION:
+			if ((r = parse_key_constraint_extension(m,
+			    sk_providerp, dcsp, ndcsp,
+			    cert_onlyp, certs, ncerts)) != 0)
+				goto out; /* error already logged */
+			break;
+		default:
+			error_f("Unknown constraint %d", ctype);
+			r = SSH_ERR_FEATURE_UNSUPPORTED;
+			goto out;
+		}
+	}
+	/* success */
+	r = 0;
+ out:
+	return r;
+}
+
+static void
+process_add_identity(SocketEntry *e)
+{
+	Identity *id;
+	int success = 0, confirm = 0;
+	char *fp, *comment = NULL, *sk_provider = NULL;
+	char canonical_provider[PATH_MAX];
+	time_t death = 0;
+	u_int seconds = 0;
+	struct dest_constraint *dest_constraints = NULL;
+	size_t ndest_constraints = 0;
+	struct sshkey *k = NULL;
+	int r = SSH_ERR_INTERNAL_ERROR;
+
+	debug2_f("entering");
+	if ((r = sshkey_private_deserialize(e->request, &k)) != 0 ||
+	    k == NULL ||
+	    (r = sshbuf_get_cstring(e->request, &comment, NULL)) != 0) {
+		error_fr(r, "parse");
+		goto out;
+	}
+	if (parse_key_constraints(e->request, k, &death, &seconds, &confirm,
+	    &sk_provider, &dest_constraints, &ndest_constraints,
+	    NULL, NULL, NULL) != 0) {
+		error_f("failed to parse constraints");
+		sshbuf_reset(e->request);
+		goto out;
+	}
+	dump_dest_constraints(__func__, dest_constraints, ndest_constraints);
+
+	if (sk_provider != NULL) {
+		if (!sshkey_is_sk(k)) {
+			error("Cannot add provider: %s is not an "
+			    "authenticator-hosted key", sshkey_type(k));
+			goto out;
+		}
+		if (strcasecmp(sk_provider, "internal") == 0) {
+			debug_f("internal provider");
+		} else {
+			if (socket_is_remote(e) && !remote_add_provider) {
+				verbose("failed add of SK provider \"%.100s\": "
+				    "remote addition of providers is disabled",
+				    sk_provider);
+				goto out;
+			}
+			if (realpath(sk_provider, canonical_provider) == NULL) {
+				verbose("failed provider \"%.100s\": "
+				    "realpath: %s", sk_provider,
+				    strerror(errno));
+				goto out;
+			}
+			free(sk_provider);
+			sk_provider = xstrdup(canonical_provider);
+			if (match_pattern_list(sk_provider,
+			    allowed_providers, 0) != 1) {
+				error("Refusing add key: "
+				    "provider %s not allowed", sk_provider);
+				goto out;
+			}
+		}
+	}
+	if ((r = sshkey_shield_private(k)) != 0) {
+		error_fr(r, "shield private");
+		goto out;
+	}
+	if (lifetime && !death)
+		death = monotime() + lifetime;
+	if ((id = lookup_identity(k)) == NULL) {
+		id = xcalloc(1, sizeof(Identity));
+		TAILQ_INSERT_TAIL(&idtab->idlist, id, next);
+		/* Increment the number of identities. */
+		idtab->nentries++;
+	} else {
+		/* identity not visible, do not update */
+		if (identity_permitted(id, e, NULL, NULL, NULL) != 0)
+			goto out; /* error already logged */
+		/* key state might have been updated */
+		sshkey_free(id->key);
+		free(id->comment);
+		free(id->sk_provider);
+		free_dest_constraints(id->dest_constraints,
+		    id->ndest_constraints);
+	}
+	/* success */
+	id->key = k;
+	id->comment = comment;
+	id->death = death;
+	id->confirm = confirm;
+	id->sk_provider = sk_provider;
+	id->dest_constraints = dest_constraints;
+	id->ndest_constraints = ndest_constraints;
+
+	if ((fp = sshkey_fingerprint(k, SSH_FP_HASH_DEFAULT,
+	    SSH_FP_DEFAULT)) == NULL)
+		fatal_f("sshkey_fingerprint failed");
+	debug_f("add %s %s \"%.100s\" (life: %u) (confirm: %u) "
+	    "(provider: %s) (destination constraints: %zu)",
+	    sshkey_ssh_name(k), fp, comment, seconds, confirm,
+	    sk_provider == NULL ? "none" : sk_provider, ndest_constraints);
+	free(fp);
+	/* transferred */
+	k = NULL;
+	comment = NULL;
+	sk_provider = NULL;
+	dest_constraints = NULL;
+	ndest_constraints = 0;
+	success = 1;
+ out:
+	free(sk_provider);
+	free(comment);
+	sshkey_free(k);
+	free_dest_constraints(dest_constraints, ndest_constraints);
+	send_status(e, success);
+}
+
+/* XXX todo: encrypt sensitive data with passphrase */
+static void
+process_lock_agent(SocketEntry *e, int lock)
+{
+	int r, success = 0, delay;
+	char *passwd;
+	u_char passwdhash[LOCK_SIZE];
+	static u_int fail_count = 0;
+	size_t pwlen;
+
+	debug2_f("entering");
+	/*
+	 * This is deliberately fatal: the user has requested that we lock,
+	 * but we can't parse their request properly. The only safe thing to
+	 * do is abort.
+	 */
+	if ((r = sshbuf_get_cstring(e->request, &passwd, &pwlen)) != 0)
+		fatal_fr(r, "parse");
+	if (pwlen == 0) {
+		debug("empty password not supported");
+	} else if (locked && !lock) {
+		if (bcrypt_pbkdf(passwd, pwlen, lock_salt, sizeof(lock_salt),
+		    passwdhash, sizeof(passwdhash), LOCK_ROUNDS) < 0)
+			fatal("bcrypt_pbkdf");
+		if (timingsafe_bcmp(passwdhash, lock_pwhash, LOCK_SIZE) == 0) {
+			debug("agent unlocked");
+			locked = 0;
+			fail_count = 0;
+			explicit_bzero(lock_pwhash, sizeof(lock_pwhash));
+			success = 1;
+		} else {
+			/* delay in 0.1s increments up to 10s */
+			if (fail_count < 100)
+				fail_count++;
+			delay = 100000 * fail_count;
+			debug("unlock failed, delaying %0.1lf seconds",
+			    (double)delay/1000000);
+			usleep(delay);
+		}
+		explicit_bzero(passwdhash, sizeof(passwdhash));
+	} else if (!locked && lock) {
+		debug("agent locked");
+		locked = 1;
+		arc4random_buf(lock_salt, sizeof(lock_salt));
+		if (bcrypt_pbkdf(passwd, pwlen, lock_salt, sizeof(lock_salt),
+		    lock_pwhash, sizeof(lock_pwhash), LOCK_ROUNDS) < 0)
+			fatal("bcrypt_pbkdf");
+		success = 1;
+	}
+	freezero(passwd, pwlen);
+	send_status(e, success);
+}
+
+static void
+no_identities(SocketEntry *e)
+{
+	struct sshbuf *msg;
+	int r;
+
+	if ((msg = sshbuf_new()) == NULL)
+		fatal_f("sshbuf_new failed");
+	if ((r = sshbuf_put_u8(msg, SSH2_AGENT_IDENTITIES_ANSWER)) != 0 ||
+	    (r = sshbuf_put_u32(msg, 0)) != 0 ||
+	    (r = sshbuf_put_stringb(e->output, msg)) != 0)
+		fatal_fr(r, "compose");
+	sshbuf_free(msg);
+}
+
+/* Add an identity to idlist; takes ownership of 'key' and 'comment' */
+static void
+add_p11_identity(struct sshkey *key, char *comment, const char *provider,
+    time_t death, int confirm, struct dest_constraint *dest_constraints,
+    size_t ndest_constraints)
+{
+	Identity *id;
+
+	if (lookup_identity(key) != NULL) {
+		sshkey_free(key);
+		free(comment);
+		return;
+	}
+	id = xcalloc(1, sizeof(Identity));
+	id->key = key;
+	id->comment = comment;
+	id->provider = xstrdup(provider);
+	id->death = death;
+	id->confirm = confirm;
+	id->dest_constraints = dup_dest_constraints(dest_constraints,
+	    ndest_constraints);
+	id->ndest_constraints = ndest_constraints;
+	TAILQ_INSERT_TAIL(&idtab->idlist, id, next);
+	idtab->nentries++;
+}
+
+#ifdef ENABLE_PKCS11
+static void
+process_add_smartcard_key(SocketEntry *e)
+{
+	char *provider = NULL, *pin = NULL, canonical_provider[PATH_MAX];
+	char **comments = NULL;
+	int r, i, count = 0, success = 0, confirm = 0;
+	u_int seconds = 0;
+	time_t death = 0;
+	struct sshkey **keys = NULL, *k;
+	struct dest_constraint *dest_constraints = NULL;
+	size_t j, ndest_constraints = 0, ncerts = 0;
+	struct sshkey **certs = NULL;
+	int cert_only = 0;
+
+	debug2_f("entering");
+	if ((r = sshbuf_get_cstring(e->request, &provider, NULL)) != 0 ||
+	    (r = sshbuf_get_cstring(e->request, &pin, NULL)) != 0) {
+		error_fr(r, "parse");
+		goto send;
+	}
+	if (parse_key_constraints(e->request, NULL, &death, &seconds, &confirm,
+	    NULL, &dest_constraints, &ndest_constraints, &cert_only,
+	    &ncerts, &certs) != 0) {
+		error_f("failed to parse constraints");
+		goto send;
+	}
+	dump_dest_constraints(__func__, dest_constraints, ndest_constraints);
+	if (socket_is_remote(e) && !remote_add_provider) {
+		verbose("failed PKCS#11 add of \"%.100s\": remote addition of "
+		    "providers is disabled", provider);
+		goto send;
+	}
+	if (realpath(provider, canonical_provider) == NULL) {
+		verbose("failed PKCS#11 add of \"%.100s\": realpath: %s",
+		    provider, strerror(errno));
+		goto send;
+	}
+	if (match_pattern_list(canonical_provider, allowed_providers, 0) != 1) {
+		verbose("refusing PKCS#11 add of \"%.100s\": "
+		    "provider not allowed", canonical_provider);
+		goto send;
+	}
+	debug_f("add %.100s", canonical_provider);
+	if (lifetime && !death)
+		death = monotime() + lifetime;
+
+	count = pkcs11_add_provider(canonical_provider, pin, &keys, &comments);
+	for (i = 0; i < count; i++) {
+		if (comments[i] == NULL || comments[i][0] == '\0') {
+			free(comments[i]);
+			comments[i] = xstrdup(canonical_provider);
+		}
+		for (j = 0; j < ncerts; j++) {
+			if (!sshkey_is_cert(certs[j]))
+				continue;
+			if (!sshkey_equal_public(keys[i], certs[j]))
+				continue;
+			if (pkcs11_make_cert(keys[i], certs[j], &k) != 0)
+				continue;
+			add_p11_identity(k, xstrdup(comments[i]),
+			    canonical_provider, death, confirm,
+			    dest_constraints, ndest_constraints);
+			success = 1;
+		}
+		if (!cert_only && lookup_identity(keys[i]) == NULL) {
+			add_p11_identity(keys[i], comments[i],
+			    canonical_provider, death, confirm,
+			    dest_constraints, ndest_constraints);
+			keys[i] = NULL;		/* transferred */
+			comments[i] = NULL;	/* transferred */
+			success = 1;
+		}
+		/* XXX update constraints for existing keys */
+		sshkey_free(keys[i]);
+		free(comments[i]);
+	}
+send:
+	free(pin);
+	free(provider);
+	free(keys);
+	free(comments);
+	free_dest_constraints(dest_constraints, ndest_constraints);
+	for (j = 0; j < ncerts; j++)
+		sshkey_free(certs[j]);
+	free(certs);
+	send_status(e, success);
+}
+
+static void
+process_remove_smartcard_key(SocketEntry *e)
+{
+	char *provider = NULL, *pin = NULL, canonical_provider[PATH_MAX];
+	int r, success = 0;
+	Identity *id, *nxt;
+
+	debug2_f("entering");
+	if ((r = sshbuf_get_cstring(e->request, &provider, NULL)) != 0 ||
+	    (r = sshbuf_get_cstring(e->request, &pin, NULL)) != 0) {
+		error_fr(r, "parse");
+		goto send;
+	}
+	free(pin);
+
+	if (realpath(provider, canonical_provider) == NULL) {
+		verbose("failed PKCS#11 add of \"%.100s\": realpath: %s",
+		    provider, strerror(errno));
+		goto send;
+	}
+
+	debug_f("remove %.100s", canonical_provider);
+	for (id = TAILQ_FIRST(&idtab->idlist); id; id = nxt) {
+		nxt = TAILQ_NEXT(id, next);
+		/* Skip file--based keys */
+		if (id->provider == NULL)
+			continue;
+		if (!strcmp(canonical_provider, id->provider)) {
+			TAILQ_REMOVE(&idtab->idlist, id, next);
+			free_identity(id);
+			idtab->nentries--;
+		}
+	}
+	if (pkcs11_del_provider(canonical_provider) == 0)
+		success = 1;
+	else
+		error_f("pkcs11_del_provider failed");
+send:
+	free(provider);
+	send_status(e, success);
+}
+#endif /* ENABLE_PKCS11 */
+
+static int
+process_ext_session_bind(SocketEntry *e)
+{
+	int r, sid_match, key_match;
+	struct sshkey *key = NULL;
+	struct sshbuf *sid = NULL, *sig = NULL;
+	char *fp = NULL;
+	size_t i;
+	u_char fwd = 0;
+
+	debug2_f("entering");
+	e->session_bind_attempted = 1;
+	if ((r = sshkey_froms(e->request, &key)) != 0 ||
+	    (r = sshbuf_froms(e->request, &sid)) != 0 ||
+	    (r = sshbuf_froms(e->request, &sig)) != 0 ||
+	    (r = sshbuf_get_u8(e->request, &fwd)) != 0) {
+		error_fr(r, "parse");
+		goto out;
+	}
+	if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
+	    SSH_FP_DEFAULT)) == NULL)
+		fatal_f("fingerprint failed");
+	/* check signature with hostkey on session ID */
+	if ((r = sshkey_verify(key, sshbuf_ptr(sig), sshbuf_len(sig),
+	    sshbuf_ptr(sid), sshbuf_len(sid), NULL, 0, NULL)) != 0) {
+		error_fr(r, "sshkey_verify for %s %s", sshkey_type(key), fp);
+		goto out;
+	}
+	/* check whether sid/key already recorded */
+	for (i = 0; i < e->nsession_ids; i++) {
+		if (!e->session_ids[i].forwarded) {
+			error_f("attempt to bind session ID to socket "
+			    "previously bound for authentication attempt");
+			r = -1;
+			goto out;
+		}
+		sid_match = buf_equal(sid, e->session_ids[i].sid) == 0;
+		key_match = sshkey_equal(key, e->session_ids[i].key);
+		if (sid_match && key_match) {
+			debug_f("session ID already recorded for %s %s",
+			    sshkey_type(key), fp);
+			r = 0;
+			goto out;
+		} else if (sid_match) {
+			error_f("session ID recorded against different key "
+			    "for %s %s", sshkey_type(key), fp);
+			r = -1;
+			goto out;
+		}
+		/*
+		 * new sid with previously-seen key can happen, e.g. multiple
+		 * connections to the same host.
+		 */
+	}
+	/* record new key/sid */
+	if (e->nsession_ids >= AGENT_MAX_SESSION_IDS) {
+		error_f("too many session IDs recorded");
+		goto out;
+	}
+	e->session_ids = xrecallocarray(e->session_ids, e->nsession_ids,
+	    e->nsession_ids + 1, sizeof(*e->session_ids));
+	i = e->nsession_ids++;
+	debug_f("recorded %s %s (slot %zu of %d)", sshkey_type(key), fp, i,
+	    AGENT_MAX_SESSION_IDS);
+	e->session_ids[i].key = key;
+	e->session_ids[i].forwarded = fwd != 0;
+	key = NULL; /* transferred */
+	/* can't transfer sid; it's refcounted and scoped to request's life */
+	if ((e->session_ids[i].sid = sshbuf_new()) == NULL)
+		fatal_f("sshbuf_new");
+	if ((r = sshbuf_putb(e->session_ids[i].sid, sid)) != 0)
+		fatal_fr(r, "sshbuf_putb session ID");
+	/* success */
+	r = 0;
+ out:
+	free(fp);
+	sshkey_free(key);
+	sshbuf_free(sid);
+	sshbuf_free(sig);
+	return r == 0 ? 1 : 0;
+}
+
+static void
+process_extension(SocketEntry *e)
+{
+	int r, success = 0;
+	char *name;
+
+	debug2_f("entering");
+	if ((r = sshbuf_get_cstring(e->request, &name, NULL)) != 0) {
+		error_fr(r, "parse");
+		goto send;
+	}
+	if (strcmp(name, "session-bind@openssh.com") == 0)
+		success = process_ext_session_bind(e);
+	else
+		debug_f("unsupported extension \"%s\"", name);
+	free(name);
+send:
+	send_status(e, success);
+}
+/*
+ * dispatch incoming message.
+ * returns 1 on success, 0 for incomplete messages or -1 on error.
+ */
+static int
+process_message(u_int socknum)
+{
+	u_int msg_len;
+	u_char type;
+	const u_char *cp;
+	int r;
+	SocketEntry *e;
+
+	if (socknum >= sockets_alloc)
+		fatal_f("sock %u >= allocated %u", socknum, sockets_alloc);
+	e = &sockets[socknum];
+
+	if (sshbuf_len(e->input) < 5)
+		return 0;		/* Incomplete message header. */
+	cp = sshbuf_ptr(e->input);
+	msg_len = PEEK_U32(cp);
+	if (msg_len > AGENT_MAX_LEN) {
+		debug_f("socket %u (fd=%d) message too long %u > %u",
+		    socknum, e->fd, msg_len, AGENT_MAX_LEN);
+		return -1;
+	}
+	if (sshbuf_len(e->input) < msg_len + 4)
+		return 0;		/* Incomplete message body. */
+
+	/* move the current input to e->request */
+	sshbuf_reset(e->request);
+	if ((r = sshbuf_get_stringb(e->input, e->request)) != 0 ||
+	    (r = sshbuf_get_u8(e->request, &type)) != 0) {
+		if (r == SSH_ERR_MESSAGE_INCOMPLETE ||
+		    r == SSH_ERR_STRING_TOO_LARGE) {
+			error_fr(r, "parse");
+			return -1;
+		}
+		fatal_fr(r, "parse");
+	}
+
+	debug_f("socket %u (fd=%d) type %d", socknum, e->fd, type);
+
+	/* check whether agent is locked */
+	if (locked && type != SSH_AGENTC_UNLOCK) {
+		sshbuf_reset(e->request);
+		switch (type) {
+		case SSH2_AGENTC_REQUEST_IDENTITIES:
+			/* send empty lists */
+			no_identities(e);
+			break;
+		default:
+			/* send a fail message for all other request types */
+			send_status(e, 0);
+		}
+		return 1;
+	}
+
+	switch (type) {
+	case SSH_AGENTC_LOCK:
+	case SSH_AGENTC_UNLOCK:
+		process_lock_agent(e, type == SSH_AGENTC_LOCK);
+		break;
+	case SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES:
+		process_remove_all_identities(e); /* safe for !WITH_SSH1 */
+		break;
+	/* ssh2 */
+	case SSH2_AGENTC_SIGN_REQUEST:
+		process_sign_request2(e);
+		break;
+	case SSH2_AGENTC_REQUEST_IDENTITIES:
+		process_request_identities(e);
+		break;
+	case SSH2_AGENTC_ADD_IDENTITY:
+	case SSH2_AGENTC_ADD_ID_CONSTRAINED:
+		process_add_identity(e);
+		break;
+	case SSH2_AGENTC_REMOVE_IDENTITY:
+		process_remove_identity(e);
+		break;
+	case SSH2_AGENTC_REMOVE_ALL_IDENTITIES:
+		process_remove_all_identities(e);
+		break;
+#ifdef ENABLE_PKCS11
+	case SSH_AGENTC_ADD_SMARTCARD_KEY:
+	case SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED:
+		process_add_smartcard_key(e);
+		break;
+	case SSH_AGENTC_REMOVE_SMARTCARD_KEY:
+		process_remove_smartcard_key(e);
+		break;
+#endif /* ENABLE_PKCS11 */
+	case SSH_AGENTC_EXTENSION:
+		process_extension(e);
+		break;
+	default:
+		/* Unknown message.  Respond with failure. */
+		error("Unknown message %d", type);
+		sshbuf_reset(e->request);
+		send_status(e, 0);
+		break;
+	}
+	return 1;
+}
+
+static void
+new_socket(sock_type type, int fd)
+{
+	u_int i, old_alloc, new_alloc;
+
+	debug_f("type = %s", type == AUTH_CONNECTION ? "CONNECTION" :
+	    (type == AUTH_SOCKET ? "SOCKET" : "UNKNOWN"));
+	set_nonblock(fd);
+
+	if (fd > max_fd)
+		max_fd = fd;
+
+	for (i = 0; i < sockets_alloc; i++)
+		if (sockets[i].type == AUTH_UNUSED) {
+			sockets[i].fd = fd;
+			if ((sockets[i].input = sshbuf_new()) == NULL ||
+			    (sockets[i].output = sshbuf_new()) == NULL ||
+			    (sockets[i].request = sshbuf_new()) == NULL)
+				fatal_f("sshbuf_new failed");
+			sockets[i].type = type;
+			return;
+		}
+	old_alloc = sockets_alloc;
+	new_alloc = sockets_alloc + 10;
+	sockets = xrecallocarray(sockets, old_alloc, new_alloc,
+	    sizeof(sockets[0]));
+	for (i = old_alloc; i < new_alloc; i++)
+		sockets[i].type = AUTH_UNUSED;
+	sockets_alloc = new_alloc;
+	sockets[old_alloc].fd = fd;
+	if ((sockets[old_alloc].input = sshbuf_new()) == NULL ||
+	    (sockets[old_alloc].output = sshbuf_new()) == NULL ||
+	    (sockets[old_alloc].request = sshbuf_new()) == NULL)
+		fatal_f("sshbuf_new failed");
+	sockets[old_alloc].type = type;
+}
+
+static int
+handle_socket_read(u_int socknum)
+{
+	struct sockaddr_un sunaddr;
+	socklen_t slen;
+	uid_t euid;
+	gid_t egid;
+	int fd;
+
+	slen = sizeof(sunaddr);
+	fd = accept(sockets[socknum].fd, (struct sockaddr *)&sunaddr, &slen);
+	if (fd == -1) {
+		error("accept from AUTH_SOCKET: %s", strerror(errno));
+		return -1;
+	}
+	if (getpeereid(fd, &euid, &egid) == -1) {
+		error("getpeereid %d failed: %s", fd, strerror(errno));
+		close(fd);
+		return -1;
+	}
+	if ((euid != 0) && (getuid() != euid)) {
+		error("uid mismatch: peer euid %u != uid %u",
+		    (u_int) euid, (u_int) getuid());
+		close(fd);
+		return -1;
+	}
+	new_socket(AUTH_CONNECTION, fd);
+	return 0;
+}
+
+static int
+handle_conn_read(u_int socknum)
+{
+	char buf[AGENT_RBUF_LEN];
+	ssize_t len;
+	int r;
+
+	if ((len = read(sockets[socknum].fd, buf, sizeof(buf))) <= 0) {
+		if (len == -1) {
+			if (errno == EAGAIN || errno == EINTR)
+				return 0;
+			error_f("read error on socket %u (fd %d): %s",
+			    socknum, sockets[socknum].fd, strerror(errno));
+		}
+		return -1;
+	}
+	if ((r = sshbuf_put(sockets[socknum].input, buf, len)) != 0)
+		fatal_fr(r, "compose");
+	explicit_bzero(buf, sizeof(buf));
+	for (;;) {
+		if ((r = process_message(socknum)) == -1)
+			return -1;
+		else if (r == 0)
+			break;
+	}
+	return 0;
+}
+
+static int
+handle_conn_write(u_int socknum)
+{
+	ssize_t len;
+	int r;
+
+	if (sshbuf_len(sockets[socknum].output) == 0)
+		return 0; /* shouldn't happen */
+	if ((len = write(sockets[socknum].fd,
+	    sshbuf_ptr(sockets[socknum].output),
+	    sshbuf_len(sockets[socknum].output))) <= 0) {
+		if (len == -1) {
+			if (errno == EAGAIN || errno == EINTR)
+				return 0;
+			error_f("read error on socket %u (fd %d): %s",
+			    socknum, sockets[socknum].fd, strerror(errno));
+		}
+		return -1;
+	}
+	if ((r = sshbuf_consume(sockets[socknum].output, len)) != 0)
+		fatal_fr(r, "consume");
+	return 0;
+}
+
+static void
+after_poll(struct pollfd *pfd, size_t npfd, u_int maxfds)
+{
+	size_t i;
+	u_int socknum, activefds = npfd;
+
+	for (i = 0; i < npfd; i++) {
+		if (pfd[i].revents == 0)
+			continue;
+		/* Find sockets entry */
+		for (socknum = 0; socknum < sockets_alloc; socknum++) {
+			if (sockets[socknum].type != AUTH_SOCKET &&
+			    sockets[socknum].type != AUTH_CONNECTION)
+				continue;
+			if (pfd[i].fd == sockets[socknum].fd)
+				break;
+		}
+		if (socknum >= sockets_alloc) {
+			error_f("no socket for fd %d", pfd[i].fd);
+			continue;
+		}
+		/* Process events */
+		switch (sockets[socknum].type) {
+		case AUTH_SOCKET:
+			if ((pfd[i].revents & (POLLIN|POLLERR)) == 0)
+				break;
+			if (npfd > maxfds) {
+				debug3("out of fds (active %u >= limit %u); "
+				    "skipping accept", activefds, maxfds);
+				break;
+			}
+			if (handle_socket_read(socknum) == 0)
+				activefds++;
+			break;
+		case AUTH_CONNECTION:
+			if ((pfd[i].revents & (POLLIN|POLLHUP|POLLERR)) != 0 &&
+			    handle_conn_read(socknum) != 0)
+				goto close_sock;
+			if ((pfd[i].revents & (POLLOUT|POLLHUP)) != 0 &&
+			    handle_conn_write(socknum) != 0) {
+ close_sock:
+				if (activefds == 0)
+					fatal("activefds == 0 at close_sock");
+				close_socket(&sockets[socknum]);
+				activefds--;
+				break;
+			}
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+static int
+prepare_poll(struct pollfd **pfdp, size_t *npfdp, int *timeoutp, u_int maxfds)
+{
+	struct pollfd *pfd = *pfdp;
+	size_t i, j, npfd = 0;
+	time_t deadline;
+	int r;
+
+	/* Count active sockets */
+	for (i = 0; i < sockets_alloc; i++) {
+		switch (sockets[i].type) {
+		case AUTH_SOCKET:
+		case AUTH_CONNECTION:
+			npfd++;
+			break;
+		case AUTH_UNUSED:
+			break;
+		default:
+			fatal("Unknown socket type %d", sockets[i].type);
+			break;
+		}
+	}
+	if (npfd != *npfdp &&
+	    (pfd = recallocarray(pfd, *npfdp, npfd, sizeof(*pfd))) == NULL)
+		fatal_f("recallocarray failed");
+	*pfdp = pfd;
+	*npfdp = npfd;
+
+	for (i = j = 0; i < sockets_alloc; i++) {
+		switch (sockets[i].type) {
+		case AUTH_SOCKET:
+			if (npfd > maxfds) {
+				debug3("out of fds (active %zu >= limit %u); "
+				    "skipping arming listener", npfd, maxfds);
+				break;
+			}
+			pfd[j].fd = sockets[i].fd;
+			pfd[j].revents = 0;
+			pfd[j].events = POLLIN;
+			j++;
+			break;
+		case AUTH_CONNECTION:
+			pfd[j].fd = sockets[i].fd;
+			pfd[j].revents = 0;
+			/*
+			 * Only prepare to read if we can handle a full-size
+			 * input read buffer and enqueue a max size reply..
+			 */
+			if ((r = sshbuf_check_reserve(sockets[i].input,
+			    AGENT_RBUF_LEN)) == 0 &&
+			    (r = sshbuf_check_reserve(sockets[i].output,
+			    AGENT_MAX_LEN)) == 0)
+				pfd[j].events = POLLIN;
+			else if (r != SSH_ERR_NO_BUFFER_SPACE)
+				fatal_fr(r, "reserve");
+			if (sshbuf_len(sockets[i].output) > 0)
+				pfd[j].events |= POLLOUT;
+			j++;
+			break;
+		default:
+			break;
+		}
+	}
+	deadline = reaper();
+	if (parent_alive_interval != 0)
+		deadline = (deadline == 0) ? parent_alive_interval :
+		    MINIMUM(deadline, parent_alive_interval);
+	if (deadline == 0) {
+		*timeoutp = -1; /* INFTIM */
+	} else {
+		if (deadline > INT_MAX / 1000)
+			*timeoutp = INT_MAX / 1000;
+		else
+			*timeoutp = deadline * 1000;
+	}
+	return (1);
+}
+
+static void
+cleanup_socket(void)
+{
+	if (cleanup_pid != 0 && getpid() != cleanup_pid)
+		return;
+	debug_f("cleanup");
+	if (socket_name[0])
+		unlink(socket_name);
+	if (socket_dir[0])
+		rmdir(socket_dir);
+}
+
+void
+cleanup_exit(int i)
+{
+	cleanup_socket();
+	_exit(i);
+}
+
+static void
+cleanup_handler(int sig)
+{
+	cleanup_socket();
+#ifdef ENABLE_PKCS11
+	pkcs11_terminate();
+#endif
+	_exit(2);
+}
+
+static void
+check_parent_exists(void)
+{
+	/*
+	 * If our parent has exited then getppid() will return (pid_t)1,
+	 * so testing for that should be safe.
+	 */
+	if (parent_pid != -1 && getppid() != parent_pid) {
+		/* printf("Parent has died - Authentication agent exiting.\n"); */
+		cleanup_socket();
+		_exit(2);
+	}
+}
+
+static void
+usage(void)
+{
+	fprintf(stderr,
+	    "usage: ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]\n"
+	    "                 [-O option] [-P allowed_providers] [-t life]\n"
+	    "       ssh-agent [-a bind_address] [-E fingerprint_hash] [-O option]\n"
+	    "                 [-P allowed_providers] [-t life] command [arg ...]\n"
+	    "       ssh-agent [-c | -s] -k\n");
+	exit(1);
+}
+
+int
+main(int ac, char **av)
+{
+	int c_flag = 0, d_flag = 0, D_flag = 0, k_flag = 0, s_flag = 0;
+	int sock, ch, result, saved_errno;
+	char *shell, *format, *pidstr, *agentsocket = NULL;
+#ifdef HAVE_SETRLIMIT
+	struct rlimit rlim;
+#endif
+	extern int optind;
+	extern char *optarg;
+	pid_t pid;
+	char pidstrbuf[1 + 3 * sizeof pid];
+	size_t len;
+	mode_t prev_mask;
+	int timeout = -1; /* INFTIM */
+	struct pollfd *pfd = NULL;
+	size_t npfd = 0;
+	u_int maxfds;
+
+	/* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
+	sanitise_stdfd();
+
+	/* drop */
+	(void)setegid(getgid());
+	(void)setgid(getgid());
+
+	platform_disable_tracing(0);	/* strict=no */
+
+#ifdef RLIMIT_NOFILE
+	if (getrlimit(RLIMIT_NOFILE, &rlim) == -1)
+		fatal("%s: getrlimit: %s", __progname, strerror(errno));
+#endif
+
+	__progname = ssh_get_progname(av[0]);
+	seed_rng();
+
+	while ((ch = getopt(ac, av, "cDdksE:a:O:P:t:")) != -1) {
+		switch (ch) {
+		case 'E':
+			fingerprint_hash = ssh_digest_alg_by_name(optarg);
+			if (fingerprint_hash == -1)
+				fatal("Invalid hash algorithm \"%s\"", optarg);
+			break;
+		case 'c':
+			if (s_flag)
+				usage();
+			c_flag++;
+			break;
+		case 'k':
+			k_flag++;
+			break;
+		case 'O':
+			if (strcmp(optarg, "no-restrict-websafe") == 0)
+				restrict_websafe = 0;
+			else if (strcmp(optarg, "allow-remote-pkcs11") == 0)
+				remote_add_provider = 1;
+			else
+				fatal("Unknown -O option");
+			break;
+		case 'P':
+			if (allowed_providers != NULL)
+				fatal("-P option already specified");
+			allowed_providers = xstrdup(optarg);
+			break;
+		case 's':
+			if (c_flag)
+				usage();
+			s_flag++;
+			break;
+		case 'd':
+			if (d_flag || D_flag)
+				usage();
+			d_flag++;
+			break;
+		case 'D':
+			if (d_flag || D_flag)
+				usage();
+			D_flag++;
+			break;
+		case 'a':
+			agentsocket = optarg;
+			break;
+		case 't':
+			if ((lifetime = convtime(optarg)) == -1) {
+				fprintf(stderr, "Invalid lifetime\n");
+				usage();
+			}
+			break;
+		default:
+			usage();
+		}
+	}
+	ac -= optind;
+	av += optind;
+
+	if (ac > 0 && (c_flag || k_flag || s_flag || d_flag || D_flag))
+		usage();
+
+	if (allowed_providers == NULL)
+		allowed_providers = xstrdup(DEFAULT_ALLOWED_PROVIDERS);
+
+	if (ac == 0 && !c_flag && !s_flag) {
+		shell = getenv("SHELL");
+		if (shell != NULL && (len = strlen(shell)) > 2 &&
+		    strncmp(shell + len - 3, "csh", 3) == 0)
+			c_flag = 1;
+	}
+	if (k_flag) {
+		const char *errstr = NULL;
+
+		pidstr = getenv(SSH_AGENTPID_ENV_NAME);
+		if (pidstr == NULL) {
+			fprintf(stderr, "%s not set, cannot kill agent\n",
+			    SSH_AGENTPID_ENV_NAME);
+			exit(1);
+		}
+		pid = (int)strtonum(pidstr, 2, INT_MAX, &errstr);
+		if (errstr) {
+			fprintf(stderr,
+			    "%s=\"%s\", which is not a good PID: %s\n",
+			    SSH_AGENTPID_ENV_NAME, pidstr, errstr);
+			exit(1);
+		}
+		if (kill(pid, SIGTERM) == -1) {
+			perror("kill");
+			exit(1);
+		}
+		format = c_flag ? "unsetenv %s;\n" : "unset %s;\n";
+		printf(format, SSH_AUTHSOCKET_ENV_NAME);
+		printf(format, SSH_AGENTPID_ENV_NAME);
+		printf("echo Agent pid %ld killed;\n", (long)pid);
+		exit(0);
+	}
+
+	/*
+	 * Minimum file descriptors:
+	 * stdio (3) + listener (1) + syslog (1 maybe) + connection (1) +
+	 * a few spare for libc / stack protectors / sanitisers, etc.
+	 */
+#define SSH_AGENT_MIN_FDS (3+1+1+1+4)
+	if (rlim.rlim_cur < SSH_AGENT_MIN_FDS)
+		fatal("%s: file descriptor rlimit %lld too low (minimum %u)",
+		    __progname, (long long)rlim.rlim_cur, SSH_AGENT_MIN_FDS);
+	maxfds = rlim.rlim_cur - SSH_AGENT_MIN_FDS;
+
+	parent_pid = getpid();
+
+	if (agentsocket == NULL) {
+		/* Create private directory for agent socket */
+		mktemp_proto(socket_dir, sizeof(socket_dir));
+		if (mkdtemp(socket_dir) == NULL) {
+			perror("mkdtemp: private socket dir");
+			exit(1);
+		}
+		snprintf(socket_name, sizeof socket_name, "%s/agent.%ld", socket_dir,
+		    (long)parent_pid);
+	} else {
+		/* Try to use specified agent socket */
+		socket_dir[0] = '\0';
+		strlcpy(socket_name, agentsocket, sizeof socket_name);
+	}
+
+	/*
+	 * Create socket early so it will exist before command gets run from
+	 * the parent.
+	 */
+	prev_mask = umask(0177);
+	sock = unix_listener(socket_name, SSH_LISTEN_BACKLOG, 0);
+	if (sock < 0) {
+		/* XXX - unix_listener() calls error() not perror() */
+		*socket_name = '\0'; /* Don't unlink any existing file */
+		cleanup_exit(1);
+	}
+	umask(prev_mask);
+
+	/*
+	 * Fork, and have the parent execute the command, if any, or present
+	 * the socket data.  The child continues as the authentication agent.
+	 */
+	if (D_flag || d_flag) {
+		log_init(__progname,
+		    d_flag ? SYSLOG_LEVEL_DEBUG3 : SYSLOG_LEVEL_INFO,
+		    SYSLOG_FACILITY_AUTH, 1);
+		format = c_flag ? "setenv %s %s;\n" : "%s=%s; export %s;\n";
+		printf(format, SSH_AUTHSOCKET_ENV_NAME, socket_name,
+		    SSH_AUTHSOCKET_ENV_NAME);
+		printf("echo Agent pid %ld;\n", (long)parent_pid);
+		fflush(stdout);
+		goto skip;
+	}
+	pid = fork();
+	if (pid == -1) {
+		perror("fork");
+		cleanup_exit(1);
+	}
+	if (pid != 0) {		/* Parent - execute the given command. */
+		close(sock);
+		snprintf(pidstrbuf, sizeof pidstrbuf, "%ld", (long)pid);
+		if (ac == 0) {
+			format = c_flag ? "setenv %s %s;\n" : "%s=%s; export %s;\n";
+			printf(format, SSH_AUTHSOCKET_ENV_NAME, socket_name,
+			    SSH_AUTHSOCKET_ENV_NAME);
+			printf(format, SSH_AGENTPID_ENV_NAME, pidstrbuf,
+			    SSH_AGENTPID_ENV_NAME);
+			printf("echo Agent pid %ld;\n", (long)pid);
+			exit(0);
+		}
+		if (setenv(SSH_AUTHSOCKET_ENV_NAME, socket_name, 1) == -1 ||
+		    setenv(SSH_AGENTPID_ENV_NAME, pidstrbuf, 1) == -1) {
+			perror("setenv");
+			exit(1);
+		}
+		execvp(av[0], av);
+		perror(av[0]);
+		exit(1);
+	}
+	/* child */
+	log_init(__progname, SYSLOG_LEVEL_INFO, SYSLOG_FACILITY_AUTH, 0);
+
+	if (setsid() == -1) {
+		error("setsid: %s", strerror(errno));
+		cleanup_exit(1);
+	}
+
+	(void)chdir("/");
+	if (stdfd_devnull(1, 1, 1) == -1)
+		error_f("stdfd_devnull failed");
+
+#ifdef HAVE_SETRLIMIT
+	/* deny core dumps, since memory contains unencrypted private keys */
+	rlim.rlim_cur = rlim.rlim_max = 0;
+	if (setrlimit(RLIMIT_CORE, &rlim) == -1) {
+		error("setrlimit RLIMIT_CORE: %s", strerror(errno));
+		cleanup_exit(1);
+	}
+#endif
+
+skip:
+
+	cleanup_pid = getpid();
+
+#ifdef ENABLE_PKCS11
+	pkcs11_init(0);
+#endif
+	new_socket(AUTH_SOCKET, sock);
+	if (ac > 0)
+		parent_alive_interval = 10;
+	idtab_init();
+	ssh_signal(SIGPIPE, SIG_IGN);
+	ssh_signal(SIGINT, (d_flag | D_flag) ? cleanup_handler : SIG_IGN);
+	ssh_signal(SIGHUP, cleanup_handler);
+	ssh_signal(SIGTERM, cleanup_handler);
+
+	if (pledge("stdio rpath cpath unix id proc exec", NULL) == -1)
+		fatal("%s: pledge: %s", __progname, strerror(errno));
+	platform_pledge_agent();
+
+	while (1) {
+		prepare_poll(&pfd, &npfd, &timeout, maxfds);
+		result = poll(pfd, npfd, timeout);
+		saved_errno = errno;
+		if (parent_alive_interval != 0)
+			check_parent_exists();
+		(void) reaper();	/* remove expired keys */
+		if (result == -1) {
+			if (saved_errno == EINTR)
+				continue;
+			fatal("poll: %s", strerror(saved_errno));
+		} else if (result > 0)
+			after_poll(pfd, npfd, maxfds);
+	}
+	/* NOTREACHED */
+}