openssh/ssh-agent.c

/* $OpenBSD: ssh-agent.c,v 1.221 2017/04/30 23:29:10 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/param.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/socket.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
#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 "rsa.h"
#include "sshbuf.h"
#include "sshkey.h"
#include "authfd.h"
#include "compat.h"
#include "log.h"
#include "misc.h"
#include "digest.h"
#include "ssherr.h"
#include "match.h"

#ifdef ENABLE_PKCS11
#include "ssh-pkcs11.h"
#endif

#ifndef DEFAULT_PKCS11_WHITELIST
# define DEFAULT_PKCS11_WHITELIST "/usr/lib*/*,/usr/local/lib*/*"
#endif

typedef enum {
	AUTH_UNUSED,
	AUTH_SOCKET,
	AUTH_CONNECTION
} sock_type;

typedef struct {
	int fd;
	sock_type type;
	struct sshbuf *input;
	struct sshbuf *output;
	struct sshbuf *request;
} 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;
} 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];

/* PKCS#11 path whitelist */
static char *pkcs11_whitelist;

/* 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 long lifetime = 0;

static int fingerprint_hash = SSH_FP_HASH_DEFAULT;

static void
close_socket(SocketEntry *e)
{
	close(e->fd);
	e->fd = -1;
	e->type = AUTH_UNUSED;
	sshbuf_free(e->input);
	sshbuf_free(e->output);
	sshbuf_free(e->request);
}

static void
idtab_init(void)
{
	idtab = xcalloc(1, sizeof(*idtab));
	TAILQ_INIT(&idtab->idlist);
	idtab->nentries = 0;
}

static void
free_identity(Identity *id)
{
	sshkey_free(id->key);
	free(id->provider);
	free(id->comment);
	free(id);
}

/* 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)
{
	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.",
	    id->comment, p))
		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("%s: buffer error: %s", __func__, ssh_err(r));
}

/* send list of supported public keys to 'client' */
static void
process_request_identities(SocketEntry *e)
{
	Identity *id;
	struct sshbuf *msg;
	int r;

	if ((msg = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	if ((r = sshbuf_put_u8(msg, SSH2_AGENT_IDENTITIES_ANSWER)) != 0 ||
	    (r = sshbuf_put_u32(msg, idtab->nentries)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));
	TAILQ_FOREACH(id, &idtab->idlist, next) {
		if ((r = sshkey_puts(id->key, msg)) != 0 ||
		    (r = sshbuf_put_cstring(msg, id->comment)) != 0) {
			error("%s: put key/comment: %s", __func__,
			    ssh_err(r));
			continue;
		}
	}
	if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));
	sshbuf_free(msg);
}


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";
	}
	return NULL;
}

/* ssh2 only */
static void
process_sign_request2(SocketEntry *e)
{
	const u_char *data;
	u_char *signature = NULL;
	size_t dlen, slen = 0;
	u_int compat = 0, flags;
	int r, ok = -1;
	struct sshbuf *msg;
	struct sshkey *key = NULL;
	struct identity *id;

	if ((msg = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	if ((r = sshkey_froms(e->request, &key)) != 0 ||
	    (r = sshbuf_get_string_direct(e->request, &data, &dlen)) != 0 ||
	    (r = sshbuf_get_u32(e->request, &flags)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));
	if (flags & SSH_AGENT_OLD_SIGNATURE)
		compat = SSH_BUG_SIGBLOB;
	if ((id = lookup_identity(key)) == NULL) {
		verbose("%s: %s key not found", __func__, sshkey_type(key));
		goto send;
	}
	if (id->confirm && confirm_key(id) != 0) {
		verbose("%s: user refused key", __func__);
		goto send;
	}
	if ((r = sshkey_sign(id->key, &signature, &slen,
	    data, dlen, agent_decode_alg(key, flags), compat)) != 0) {
		error("%s: sshkey_sign: %s", __func__, ssh_err(r));
		goto send;
	}
	/* Success */
	ok = 0;
 send:
	sshkey_free(key);
	if (ok == 0) {
		if ((r = sshbuf_put_u8(msg, SSH2_AGENT_SIGN_RESPONSE)) != 0 ||
		    (r = sshbuf_put_string(msg, signature, slen)) != 0)
			fatal("%s: buffer error: %s", __func__, ssh_err(r));
	} else if ((r = sshbuf_put_u8(msg, SSH_AGENT_FAILURE)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));

	if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));

	sshbuf_free(msg);
	free(signature);
}

/* shared */
static void
process_remove_identity(SocketEntry *e)
{
	int r, success = 0;
	struct sshkey *key = NULL;
	Identity *id;

	if ((r = sshkey_froms(e->request, &key)) != 0) {
		error("%s: get key: %s", __func__, ssh_err(r));
		goto done;
	}
	if ((id = lookup_identity(key)) == NULL) {
		debug("%s: key not found", __func__);
		goto done;
	}
	/* We have this key, free it. */
	if (idtab->nentries < 1)
		fatal("%s: internal error: nentries %d",
		    __func__, idtab->nentries);
	TAILQ_REMOVE(&idtab->idlist, id, next);
	free_identity(id);
	idtab->nentries--;
	sshkey_free(key);
	success = 1;
 done:
	send_status(e, success);
}

static void
process_remove_all_identities(SocketEntry *e)
{
	Identity *id;

	/* 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 void
process_add_identity(SocketEntry *e)
{
	Identity *id;
	int success = 0, confirm = 0;
	u_int seconds;
	char *comment = NULL;
	time_t death = 0;
	struct sshkey *k = NULL;
	u_char ctype;
	int r = SSH_ERR_INTERNAL_ERROR;

	if ((r = sshkey_private_deserialize(e->request, &k)) != 0 ||
	    k == NULL ||
	    (r = sshbuf_get_cstring(e->request, &comment, NULL)) != 0) {
		error("%s: decode private key: %s", __func__, ssh_err(r));
		goto err;
	}

	while (sshbuf_len(e->request)) {
		if ((r = sshbuf_get_u8(e->request, &ctype)) != 0) {
			error("%s: buffer error: %s", __func__, ssh_err(r));
			goto err;
		}
		switch (ctype) {
		case SSH_AGENT_CONSTRAIN_LIFETIME:
			if ((r = sshbuf_get_u32(e->request, &seconds)) != 0) {
				error("%s: bad lifetime constraint: %s",
				    __func__, ssh_err(r));
				goto err;
			}
			death = monotime() + seconds;
			break;
		case SSH_AGENT_CONSTRAIN_CONFIRM:
			confirm = 1;
			break;
		default:
			error("%s: Unknown constraint %d", __func__, ctype);
 err:
			sshbuf_reset(e->request);
			free(comment);
			sshkey_free(k);
			goto send;
		}
	}

	success = 1;
	if (lifetime && !death)
		death = monotime() + lifetime;
	if ((id = lookup_identity(k)) == NULL) {
		id = xcalloc(1, sizeof(Identity));
		id->key = k;
		TAILQ_INSERT_TAIL(&idtab->idlist, id, next);
		/* Increment the number of identities. */
		idtab->nentries++;
	} else {
		sshkey_free(k);
		free(id->comment);
	}
	id->comment = comment;
	id->death = death;
	id->confirm = confirm;
send:
	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;

	if ((r = sshbuf_get_cstring(e->request, &passwd, &pwlen)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));
	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;
	}
	explicit_bzero(passwd, pwlen);
	free(passwd);
	send_status(e, success);
}

static void
no_identities(SocketEntry *e)
{
	struct sshbuf *msg;
	int r;

	if ((msg = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	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("%s: buffer error: %s", __func__, ssh_err(r));
	sshbuf_free(msg);
}

#ifdef ENABLE_PKCS11
static void
process_add_smartcard_key(SocketEntry *e)
{
	char *provider = NULL, *pin, canonical_provider[PATH_MAX];
	int r, i, count = 0, success = 0, confirm = 0;
	u_int seconds;
	time_t death = 0;
	u_char type;
	struct sshkey **keys = NULL, *k;
	Identity *id;

	if ((r = sshbuf_get_cstring(e->request, &provider, NULL)) != 0 ||
	    (r = sshbuf_get_cstring(e->request, &pin, NULL)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));

	while (sshbuf_len(e->request)) {
		if ((r = sshbuf_get_u8(e->request, &type)) != 0)
			fatal("%s: buffer error: %s", __func__, ssh_err(r));
		switch (type) {
		case SSH_AGENT_CONSTRAIN_LIFETIME:
			if ((r = sshbuf_get_u32(e->request, &seconds)) != 0)
				fatal("%s: buffer error: %s",
				    __func__, ssh_err(r));
			death = monotime() + seconds;
			break;
		case SSH_AGENT_CONSTRAIN_CONFIRM:
			confirm = 1;
			break;
		default:
			error("%s: Unknown constraint type %d", __func__, type);
			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, pkcs11_whitelist, 0) != 1) {
		verbose("refusing PKCS#11 add of \"%.100s\": "
		    "provider not whitelisted", canonical_provider);
		goto send;
	}
	debug("%s: add %.100s", __func__, canonical_provider);
	if (lifetime && !death)
		death = monotime() + lifetime;

	count = pkcs11_add_provider(canonical_provider, pin, &keys);
	for (i = 0; i < count; i++) {
		k = keys[i];
		if (lookup_identity(k) == NULL) {
			id = xcalloc(1, sizeof(Identity));
			id->key = k;
			id->provider = xstrdup(canonical_provider);
			id->comment = xstrdup(canonical_provider); /* XXX */
			id->death = death;
			id->confirm = confirm;
			TAILQ_INSERT_TAIL(&idtab->idlist, id, next);
			idtab->nentries++;
			success = 1;
		} else {
			sshkey_free(k);
		}
		keys[i] = NULL;
	}
send:
	free(pin);
	free(provider);
	free(keys);
	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;

	if ((r = sshbuf_get_cstring(e->request, &provider, NULL)) != 0 ||
	    (r = sshbuf_get_cstring(e->request, &pin, NULL)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));
	free(pin);

	if (realpath(provider, canonical_provider) == NULL) {
		verbose("failed PKCS#11 add of \"%.100s\": realpath: %s",
		    provider, strerror(errno));
		goto send;
	}

	debug("%s: remove %.100s", __func__, 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("%s: pkcs11_del_provider failed", __func__);
send:
	free(provider);
	send_status(e, success);
}
#endif /* ENABLE_PKCS11 */

/* dispatch incoming messages */

static void
process_message(SocketEntry *e)
{
	u_int msg_len;
	u_char type;
	const u_char *cp;
	int r;

	if (sshbuf_len(e->input) < 5)
		return;		/* Incomplete message. */
	cp = sshbuf_ptr(e->input);
	msg_len = PEEK_U32(cp);
	if (msg_len > 256 * 1024) {
		close_socket(e);
		return;
	}
	if (sshbuf_len(e->input) < msg_len + 4)
		return;

	/* 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)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));

	/* check wheter 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;
	}

	debug("type %d", type);
	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 */
	default:
		/* Unknown message.  Respond with failure. */
		error("Unknown message %d", type);
		sshbuf_reset(e->request);
		send_status(e, 0);
		break;
	}
}

static void
new_socket(sock_type type, int fd)
{
	u_int i, old_alloc, new_alloc;

	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)
				fatal("%s: sshbuf_new failed", __func__);
			if ((sockets[i].output = sshbuf_new()) == NULL)
				fatal("%s: sshbuf_new failed", __func__);
			if ((sockets[i].request = sshbuf_new()) == NULL)
				fatal("%s: sshbuf_new failed", __func__);
			sockets[i].type = type;
			return;
		}
	old_alloc = sockets_alloc;
	new_alloc = sockets_alloc + 10;
	sockets = xreallocarray(sockets, 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)
		fatal("%s: sshbuf_new failed", __func__);
	if ((sockets[old_alloc].output = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	if ((sockets[old_alloc].request = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	sockets[old_alloc].type = type;
}

static int
prepare_select(fd_set **fdrp, fd_set **fdwp, int *fdl, u_int *nallocp,
    struct timeval **tvpp)
{
	u_int i, sz;
	int n = 0;
	static struct timeval tv;
	time_t deadline;

	for (i = 0; i < sockets_alloc; i++) {
		switch (sockets[i].type) {
		case AUTH_SOCKET:
		case AUTH_CONNECTION:
			n = MAXIMUM(n, sockets[i].fd);
			break;
		case AUTH_UNUSED:
			break;
		default:
			fatal("Unknown socket type %d", sockets[i].type);
			break;
		}
	}

	sz = howmany(n+1, NFDBITS) * sizeof(fd_mask);
	if (*fdrp == NULL || sz > *nallocp) {
		free(*fdrp);
		free(*fdwp);
		*fdrp = xmalloc(sz);
		*fdwp = xmalloc(sz);
		*nallocp = sz;
	}
	if (n < *fdl)
		debug("XXX shrink: %d < %d", n, *fdl);
	*fdl = n;
	memset(*fdrp, 0, sz);
	memset(*fdwp, 0, sz);

	for (i = 0; i < sockets_alloc; i++) {
		switch (sockets[i].type) {
		case AUTH_SOCKET:
		case AUTH_CONNECTION:
			FD_SET(sockets[i].fd, *fdrp);
			if (sshbuf_len(sockets[i].output) > 0)
				FD_SET(sockets[i].fd, *fdwp);
			break;
		default:
			break;
		}
	}
	deadline = reaper();
	if (parent_alive_interval != 0)
		deadline = (deadline == 0) ? parent_alive_interval :
		    MINIMUM(deadline, parent_alive_interval);
	if (deadline == 0) {
		*tvpp = NULL;
	} else {
		tv.tv_sec = deadline;
		tv.tv_usec = 0;
		*tvpp = &tv;
	}
	return (1);
}

static void
after_select(fd_set *readset, fd_set *writeset)
{
	struct sockaddr_un sunaddr;
	socklen_t slen;
	char buf[1024];
	int len, sock, r;
	u_int i, orig_alloc;
	uid_t euid;
	gid_t egid;

	for (i = 0, orig_alloc = sockets_alloc; i < orig_alloc; i++)
		switch (sockets[i].type) {
		case AUTH_UNUSED:
			break;
		case AUTH_SOCKET:
			if (FD_ISSET(sockets[i].fd, readset)) {
				slen = sizeof(sunaddr);
				sock = accept(sockets[i].fd,
				    (struct sockaddr *)&sunaddr, &slen);
				if (sock < 0) {
					error("accept from AUTH_SOCKET: %s",
					    strerror(errno));
					break;
				}
				if (getpeereid(sock, &euid, &egid) < 0) {
					error("getpeereid %d failed: %s",
					    sock, strerror(errno));
					close(sock);
					break;
				}
				if ((euid != 0) && (getuid() != euid)) {
					error("uid mismatch: "
					    "peer euid %u != uid %u",
					    (u_int) euid, (u_int) getuid());
					close(sock);
					break;
				}
				new_socket(AUTH_CONNECTION, sock);
			}
			break;
		case AUTH_CONNECTION:
			if (sshbuf_len(sockets[i].output) > 0 &&
			    FD_ISSET(sockets[i].fd, writeset)) {
				len = write(sockets[i].fd,
				    sshbuf_ptr(sockets[i].output),
				    sshbuf_len(sockets[i].output));
				if (len == -1 && (errno == EAGAIN ||
				    errno == EWOULDBLOCK ||
				    errno == EINTR))
					continue;
				if (len <= 0) {
					close_socket(&sockets[i]);
					break;
				}
				if ((r = sshbuf_consume(sockets[i].output,
				    len)) != 0)
					fatal("%s: buffer error: %s",
					    __func__, ssh_err(r));
			}
			if (FD_ISSET(sockets[i].fd, readset)) {
				len = read(sockets[i].fd, buf, sizeof(buf));
				if (len == -1 && (errno == EAGAIN ||
				    errno == EWOULDBLOCK ||
				    errno == EINTR))
					continue;
				if (len <= 0) {
					close_socket(&sockets[i]);
					break;
				}
				if ((r = sshbuf_put(sockets[i].input,
				    buf, len)) != 0)
					fatal("%s: buffer error: %s",
					    __func__, ssh_err(r));
				explicit_bzero(buf, sizeof(buf));
				process_message(&sockets[i]);
			}
			break;
		default:
			fatal("Unknown type %d", sockets[i].type);
		}
}

static void
cleanup_socket(void)
{
	if (cleanup_pid != 0 && getpid() != cleanup_pid)
		return;
	debug("%s: cleanup", __func__);
	if (socket_name[0])
		unlink(socket_name);
	if (socket_dir[0])
		rmdir(socket_dir);
}

void
cleanup_exit(int i)
{
	cleanup_socket();
	_exit(i);
}

/*ARGSUSED*/
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"
	    "                 [-P pkcs11_whitelist] [-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, fd, ch, result, saved_errno;
	u_int nalloc;
	char *shell, *format, *pidstr, *agentsocket = NULL;
	fd_set *readsetp = NULL, *writesetp = NULL;
#ifdef HAVE_SETRLIMIT
	struct rlimit rlim;
#endif
	extern int optind;
	extern char *optarg;
	pid_t pid;
	char pidstrbuf[1 + 3 * sizeof pid];
	struct timeval *tvp = NULL;
	size_t len;
	mode_t prev_mask;

	ssh_malloc_init();	/* must be called before any mallocs */
	/* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
	sanitise_stdfd();

	/* drop */
	setegid(getgid());
	setgid(getgid());

	platform_disable_tracing(0);	/* strict=no */

#ifdef WITH_OPENSSL
	OpenSSL_add_all_algorithms();
#endif

	__progname = ssh_get_progname(av[0]);
	seed_rng();

	while ((ch = getopt(ac, av, "cDdksE:a: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 'P':
			if (pkcs11_whitelist != NULL)
				fatal("-P option already specified");
			pkcs11_whitelist = 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 (pkcs11_whitelist == NULL)
		pkcs11_whitelist = xstrdup(DEFAULT_PKCS11_WHITELIST);

	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);
	}
	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 ((fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
		/* XXX might close listen socket */
		(void)dup2(fd, STDIN_FILENO);
		(void)dup2(fd, STDOUT_FILENO);
		(void)dup2(fd, STDERR_FILENO);
		if (fd > 2)
			close(fd);
	}

#ifdef HAVE_SETRLIMIT
	/* deny core dumps, since memory contains unencrypted private keys */
	rlim.rlim_cur = rlim.rlim_max = 0;
	if (setrlimit(RLIMIT_CORE, &rlim) < 0) {
		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();
	signal(SIGPIPE, SIG_IGN);
	signal(SIGINT, (d_flag | D_flag) ? cleanup_handler : SIG_IGN);
	signal(SIGHUP, cleanup_handler);
	signal(SIGTERM, cleanup_handler);
	nalloc = 0;

	if (pledge("stdio rpath cpath unix id proc exec", NULL) == -1)
		fatal("%s: pledge: %s", __progname, strerror(errno));
	platform_pledge_agent();

	while (1) {
		prepare_select(&readsetp, &writesetp, &max_fd, &nalloc, &tvp);
		result = select(max_fd + 1, readsetp, writesetp, NULL, tvp);
		saved_errno = errno;
		if (parent_alive_interval != 0)
			check_parent_exists();
		(void) reaper();	/* remove expired keys */
		if (result < 0) {
			if (saved_errno == EINTR)
				continue;
			fatal("select: %s", strerror(saved_errno));
		} else if (result > 0)
			after_select(readsetp, writesetp);
	}
	/* NOTREACHED */
}