authfd.c - third_party/openssh-portable - Git at Google

 /* $OpenBSD: authfd.c,v 1.111 2018/07/09 21:59:10 markus Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
  * Functions for connecting the local authentication agent.
  *
  * 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".
  *
  * SSH2 implementation,
  * Copyright (c) 2000 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/un.h>
 #include <sys/socket.h>

 #include <fcntl.h>
 #include <stdlib.h>
 #include <signal.h>
 #include <stdarg.h>
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>

 #include "xmalloc.h"
 #include "ssh.h"
 #include "sshbuf.h"
 #include "sshkey.h"
 #include "authfd.h"
 #include "cipher.h"
 #include "compat.h"
 #include "log.h"
 #include "atomicio.h"
 #include "misc.h"
 #include "ssherr.h"

 #define MAX_AGENT_IDENTITIES	2048		/* Max keys in agent reply */
 #define MAX_AGENT_REPLY_LEN	(256 * 1024) 	/* Max bytes in agent reply */

 /* macro to check for "agent failure" message */
 #define agent_failed(x) \
     ((x == SSH_AGENT_FAILURE) || \
     (x == SSH_COM_AGENT2_FAILURE) || \
     (x == SSH2_AGENT_FAILURE))

 /* Convert success/failure response from agent to a err.h status */
 static int
 decode_reply(u_char type)
 {
 	if (agent_failed(type))
 		return SSH_ERR_AGENT_FAILURE;
 	else if (type == SSH_AGENT_SUCCESS)
 		return 0;
 	else
 		return SSH_ERR_INVALID_FORMAT;
 }

 /* Returns the number of the authentication fd, or -1 if there is none. */
 int
 ssh_get_authentication_socket(int *fdp)
 {
 	const char *authsocket;
 	int sock, oerrno;
 	struct sockaddr_un sunaddr;

 	if (fdp != NULL)
 		*fdp = -1;

 	authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME);
 	if (!authsocket)
 		return SSH_ERR_AGENT_NOT_PRESENT;

 	memset(&sunaddr, 0, sizeof(sunaddr));
 	sunaddr.sun_family = AF_UNIX;
 	strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path));

 	if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
 		return SSH_ERR_SYSTEM_ERROR;

 	/* close on exec */
 	if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 ||
 	    connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) < 0) {
 		oerrno = errno;
 		close(sock);
 		errno = oerrno;
 		return SSH_ERR_SYSTEM_ERROR;
 	}
 	if (fdp != NULL)
 		*fdp = sock;
 	else
 		close(sock);
 	return 0;
 }

 /* Communicate with agent: send request and read reply */
 static int
 ssh_request_reply(int sock, struct sshbuf *request, struct sshbuf *reply)
 {
 	int r;
 	size_t l, len;
 	char buf[1024];

 	/* Get the length of the message, and format it in the buffer. */
 	len = sshbuf_len(request);
 	POKE_U32(buf, len);

 	/* Send the length and then the packet to the agent. */
 	if (atomicio(vwrite, sock, buf, 4) != 4 ||
 	    atomicio(vwrite, sock, sshbuf_mutable_ptr(request),
 	    sshbuf_len(request)) != sshbuf_len(request))
 		return SSH_ERR_AGENT_COMMUNICATION;
 	/*
 	 * Wait for response from the agent.  First read the length of the
 	 * response packet.
 	 */
 	if (atomicio(read, sock, buf, 4) != 4)
 	    return SSH_ERR_AGENT_COMMUNICATION;

 	/* Extract the length, and check it for sanity. */
 	len = PEEK_U32(buf);
 	if (len > MAX_AGENT_REPLY_LEN)
 		return SSH_ERR_INVALID_FORMAT;

 	/* Read the rest of the response in to the buffer. */
 	sshbuf_reset(reply);
 	while (len > 0) {
 		l = len;
 		if (l > sizeof(buf))
 			l = sizeof(buf);
 		if (atomicio(read, sock, buf, l) != l)
 			return SSH_ERR_AGENT_COMMUNICATION;
 		if ((r = sshbuf_put(reply, buf, l)) != 0)
 			return r;
 		len -= l;
 	}
 	return 0;
 }

 /*
  * Closes the agent socket if it should be closed (depends on how it was
  * obtained).  The argument must have been returned by
  * ssh_get_authentication_socket().
  */
 void
 ssh_close_authentication_socket(int sock)
 {
 	if (getenv(SSH_AUTHSOCKET_ENV_NAME))
 		close(sock);
 }

 /* Lock/unlock agent */
 int
 ssh_lock_agent(int sock, int lock, const char *password)
 {
 	int r;
 	u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK;
 	struct sshbuf *msg;

 	if ((msg = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;
 	if ((r = sshbuf_put_u8(msg, type)) != 0 ||
 	    (r = sshbuf_put_cstring(msg, password)) != 0)
 		goto out;
 	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
 		goto out;
 	if ((r = sshbuf_get_u8(msg, &type)) != 0)
 		goto out;
 	r = decode_reply(type);
  out:
 	sshbuf_free(msg);
 	return r;
 }


 static int
 deserialise_identity2(struct sshbuf *ids, struct sshkey **keyp, char **commentp)
 {
 	int r;
 	char *comment = NULL;
 	const u_char *blob;
 	size_t blen;

 	if ((r = sshbuf_get_string_direct(ids, &blob, &blen)) != 0 ||
 	    (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0)
 		goto out;
 	if ((r = sshkey_from_blob(blob, blen, keyp)) != 0)
 		goto out;
 	if (commentp != NULL) {
 		*commentp = comment;
 		comment = NULL;
 	}
 	r = 0;
  out:
 	free(comment);
 	return r;
 }

 /*
  * Fetch list of identities held by the agent.
  */
 int
 ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp)
 {
 	u_char type;
 	u_int32_t num, i;
 	struct sshbuf *msg;
 	struct ssh_identitylist *idl = NULL;
 	int r;

 	/*
 	 * Send a message to the agent requesting for a list of the
 	 * identities it can represent.
 	 */
 	if ((msg = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;
 	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_REQUEST_IDENTITIES)) != 0)
 		goto out;

 	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
 		goto out;

 	/* Get message type, and verify that we got a proper answer. */
 	if ((r = sshbuf_get_u8(msg, &type)) != 0)
 		goto out;
 	if (agent_failed(type)) {
 		r = SSH_ERR_AGENT_FAILURE;
 		goto out;
 	} else if (type != SSH2_AGENT_IDENTITIES_ANSWER) {
 		r = SSH_ERR_INVALID_FORMAT;
 		goto out;
 	}

 	/* Get the number of entries in the response and check it for sanity. */
 	if ((r = sshbuf_get_u32(msg, &num)) != 0)
 		goto out;
 	if (num > MAX_AGENT_IDENTITIES) {
 		r = SSH_ERR_INVALID_FORMAT;
 		goto out;
 	}
 	if (num == 0) {
 		r = SSH_ERR_AGENT_NO_IDENTITIES;
 		goto out;
 	}

 	/* Deserialise the response into a list of keys/comments */
 	if ((idl = calloc(1, sizeof(*idl))) == NULL ||
 	    (idl->keys = calloc(num, sizeof(*idl->keys))) == NULL ||
 	    (idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) {
 		r = SSH_ERR_ALLOC_FAIL;
 		goto out;
 	}
 	for (i = 0; i < num;) {
 		if ((r = deserialise_identity2(msg, &(idl->keys[i]),
 		    &(idl->comments[i]))) != 0) {
 			if (r == SSH_ERR_KEY_TYPE_UNKNOWN) {
 				/* Gracefully skip unknown key types */
 				num--;
 				continue;
 			} else
 				goto out;
 		}
 		i++;
 	}
 	idl->nkeys = num;
 	*idlp = idl;
 	idl = NULL;
 	r = 0;
  out:
 	sshbuf_free(msg);
 	if (idl != NULL)
 		ssh_free_identitylist(idl);
 	return r;
 }

 void
 ssh_free_identitylist(struct ssh_identitylist *idl)
 {
 	size_t i;

 	if (idl == NULL)
 		return;
 	for (i = 0; i < idl->nkeys; i++) {
 		if (idl->keys != NULL)
 			sshkey_free(idl->keys[i]);
 		if (idl->comments != NULL)
 			free(idl->comments[i]);
 	}
 	free(idl);
 }

 /*
  * Sends a challenge (typically from a server via ssh(1)) to the agent,
  * and waits for a response from the agent.
  * Returns true (non-zero) if the agent gave the correct answer, zero
  * otherwise.
  */


 /* encode signature algorithm in flag bits, so we can keep the msg format */
 static u_int
 agent_encode_alg(const struct sshkey *key, const char *alg)
 {
 	if (alg != NULL && key->type == KEY_RSA) {
 		if (strcmp(alg, "rsa-sha2-256") == 0)
 			return SSH_AGENT_RSA_SHA2_256;
 		else if (strcmp(alg, "rsa-sha2-512") == 0)
 			return SSH_AGENT_RSA_SHA2_512;
 	}
 	return 0;
 }

 /* ask agent to sign data, returns err.h code on error, 0 on success */
 int
 ssh_agent_sign(int sock, const struct sshkey *key,
     u_char **sigp, size_t *lenp,
     const u_char *data, size_t datalen, const char *alg, u_int compat)
 {
 	struct sshbuf *msg;
 	u_char *sig = NULL, type = 0;
 	size_t len = 0;
 	u_int flags = 0;
 	int r = SSH_ERR_INTERNAL_ERROR;

 	*sigp = NULL;
 	*lenp = 0;

 	if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE)
 		return SSH_ERR_INVALID_ARGUMENT;
 	if ((msg = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;
 	flags |= agent_encode_alg(key, alg);
 	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 ||
 	    (r = sshkey_puts(key, msg)) != 0 ||
 	    (r = sshbuf_put_string(msg, data, datalen)) != 0 ||
 	    (r = sshbuf_put_u32(msg, flags)) != 0)
 		goto out;
 	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
 		goto out;
 	if ((r = sshbuf_get_u8(msg, &type)) != 0)
 		goto out;
 	if (agent_failed(type)) {
 		r = SSH_ERR_AGENT_FAILURE;
 		goto out;
 	} else if (type != SSH2_AGENT_SIGN_RESPONSE) {
 		r = SSH_ERR_INVALID_FORMAT;
 		goto out;
 	}
 	if ((r = sshbuf_get_string(msg, &sig, &len)) != 0)
 		goto out;
 	/* Check what we actually got back from the agent. */
 	if ((r = sshkey_check_sigtype(sig, len, alg)) != 0)
 		goto out;
 	/* success */
 	*sigp = sig;
 	*lenp = len;
 	sig = NULL;
 	len = 0;
 	r = 0;
  out:
 	freezero(sig, len);
 	sshbuf_free(msg);
 	return r;
 }

 /* Encode key for a message to the agent. */


 static int
 encode_constraints(struct sshbuf *m, u_int life, u_int confirm, u_int maxsign)
 {
 	int r;

 	if (life != 0) {
 		if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 ||
 		    (r = sshbuf_put_u32(m, life)) != 0)
 			goto out;
 	}
 	if (confirm != 0) {
 		if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0)
 			goto out;
 	}
 	if (maxsign != 0) {
 		if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_MAXSIGN)) != 0 ||
 		    (r = sshbuf_put_u32(m, maxsign)) != 0)
 			goto out;
 	}
 	r = 0;
  out:
 	return r;
 }

 /*
  * Adds an identity to the authentication server.
  * This call is intended only for use by ssh-add(1) and like applications.
  */
 int
 ssh_add_identity_constrained(int sock, const struct sshkey *key,
     const char *comment, u_int life, u_int confirm, u_int maxsign)
 {
 	struct sshbuf *msg;
 	int r, constrained = (life || confirm || maxsign);
 	u_char type;

 	if ((msg = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;

 	switch (key->type) {
 #ifdef WITH_OPENSSL
 	case KEY_RSA:
 	case KEY_RSA_CERT:
 	case KEY_DSA:
 	case KEY_DSA_CERT:
 	case KEY_ECDSA:
 	case KEY_ECDSA_CERT:
 #endif
 	case KEY_ED25519:
 	case KEY_ED25519_CERT:
 	case KEY_XMSS:
 	case KEY_XMSS_CERT:
 		type = constrained ?
 		    SSH2_AGENTC_ADD_ID_CONSTRAINED :
 		    SSH2_AGENTC_ADD_IDENTITY;
 		if ((r = sshbuf_put_u8(msg, type)) != 0 ||
 		    (r = sshkey_private_serialize_maxsign(key, msg, maxsign,
 		    NULL)) != 0 ||
 		    (r = sshbuf_put_cstring(msg, comment)) != 0)
 			goto out;
 		break;
 	default:
 		r = SSH_ERR_INVALID_ARGUMENT;
 		goto out;
 	}
 	if (constrained &&
 	    (r = encode_constraints(msg, life, confirm, maxsign)) != 0)
 		goto out;
 	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
 		goto out;
 	if ((r = sshbuf_get_u8(msg, &type)) != 0)
 		goto out;
 	r = decode_reply(type);
  out:
 	sshbuf_free(msg);
 	return r;
 }

 /*
  * Removes an identity from the authentication server.
  * This call is intended only for use by ssh-add(1) and like applications.
  */
 int
 ssh_remove_identity(int sock, struct sshkey *key)
 {
 	struct sshbuf *msg;
 	int r;
 	u_char type, *blob = NULL;
 	size_t blen;

 	if ((msg = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;

 	if (key->type != KEY_UNSPEC) {
 		if ((r = sshkey_to_blob(key, &blob, &blen)) != 0)
 			goto out;
 		if ((r = sshbuf_put_u8(msg,
 		    SSH2_AGENTC_REMOVE_IDENTITY)) != 0 ||
 		    (r = sshbuf_put_string(msg, blob, blen)) != 0)
 			goto out;
 	} else {
 		r = SSH_ERR_INVALID_ARGUMENT;
 		goto out;
 	}
 	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
 		goto out;
 	if ((r = sshbuf_get_u8(msg, &type)) != 0)
 		goto out;
 	r = decode_reply(type);
  out:
 	if (blob != NULL) {
 		explicit_bzero(blob, blen);
 		free(blob);
 	}
 	sshbuf_free(msg);
 	return r;
 }

 /*
  * Add/remove an token-based identity from the authentication server.
  * This call is intended only for use by ssh-add(1) and like applications.
  */
 int
 ssh_update_card(int sock, int add, const char *reader_id, const char *pin,
     u_int life, u_int confirm)
 {
 	struct sshbuf *msg;
 	int r, constrained = (life || confirm);
 	u_char type;

 	if (add) {
 		type = constrained ?
 		    SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED :
 		    SSH_AGENTC_ADD_SMARTCARD_KEY;
 	} else
 		type = SSH_AGENTC_REMOVE_SMARTCARD_KEY;

 	if ((msg = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;
 	if ((r = sshbuf_put_u8(msg, type)) != 0 ||
 	    (r = sshbuf_put_cstring(msg, reader_id)) != 0 ||
 	    (r = sshbuf_put_cstring(msg, pin)) != 0)
 		goto out;
 	if (constrained &&
 	    (r = encode_constraints(msg, life, confirm, 0)) != 0)
 		goto out;
 	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
 		goto out;
 	if ((r = sshbuf_get_u8(msg, &type)) != 0)
 		goto out;
 	r = decode_reply(type);
  out:
 	sshbuf_free(msg);
 	return r;
 }

 /*
  * Removes all identities from the agent.
  * This call is intended only for use by ssh-add(1) and like applications.
  *
  * This supports the SSH protocol 1 message to because, when clearing all
  * keys from an agent, we generally want to clear both protocol v1 and v2
  * keys.
  */
 int
 ssh_remove_all_identities(int sock, int version)
 {
 	struct sshbuf *msg;
 	u_char type = (version == 1) ?
 	    SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES :
 	    SSH2_AGENTC_REMOVE_ALL_IDENTITIES;
 	int r;

 	if ((msg = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;
 	if ((r = sshbuf_put_u8(msg, type)) != 0)
 		goto out;
 	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
 		goto out;
 	if ((r = sshbuf_get_u8(msg, &type)) != 0)
 		goto out;
 	r = decode_reply(type);
  out:
 	sshbuf_free(msg);
 	return r;
 }
	/* $OpenBSD: authfd.c,v 1.111 2018/07/09 21:59:10 markus Exp $ */
	/*
	* Author: Tatu Ylonen <ylo@cs.hut.fi>
	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	* All rights reserved
	* Functions for connecting the local authentication agent.
	*
	* 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".
	*
	* SSH2 implementation,
	* Copyright (c) 2000 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/un.h>
	#include <sys/socket.h>

	#include <fcntl.h>
	#include <stdlib.h>
	#include <signal.h>
	#include <stdarg.h>
	#include <string.h>
	#include <unistd.h>
	#include <errno.h>

	#include "xmalloc.h"
	#include "ssh.h"
	#include "sshbuf.h"
	#include "sshkey.h"
	#include "authfd.h"
	#include "cipher.h"
	#include "compat.h"
	#include "log.h"
	#include "atomicio.h"
	#include "misc.h"
	#include "ssherr.h"

	#define MAX_AGENT_IDENTITIES 2048 /* Max keys in agent reply */
	#define MAX_AGENT_REPLY_LEN (256 * 1024) /* Max bytes in agent reply */

	/* macro to check for "agent failure" message */
	#define agent_failed(x) \
	((x == SSH_AGENT_FAILURE) \|\| \
	(x == SSH_COM_AGENT2_FAILURE) \|\| \
	(x == SSH2_AGENT_FAILURE))

	/* Convert success/failure response from agent to a err.h status */
	static int
	decode_reply(u_char type)
	{
	if (agent_failed(type))
	return SSH_ERR_AGENT_FAILURE;
	else if (type == SSH_AGENT_SUCCESS)
	return 0;
	else
	return SSH_ERR_INVALID_FORMAT;
	}

	/* Returns the number of the authentication fd, or -1 if there is none. */
	int
	ssh_get_authentication_socket(int *fdp)
	{
	const char *authsocket;
	int sock, oerrno;
	struct sockaddr_un sunaddr;

	if (fdp != NULL)
	*fdp = -1;

	authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME);
	if (!authsocket)
	return SSH_ERR_AGENT_NOT_PRESENT;

	memset(&sunaddr, 0, sizeof(sunaddr));
	sunaddr.sun_family = AF_UNIX;
	strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path));

	if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
	return SSH_ERR_SYSTEM_ERROR;

	/* close on exec */
	if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 \|\|
	connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) < 0) {
	oerrno = errno;
	close(sock);
	errno = oerrno;
	return SSH_ERR_SYSTEM_ERROR;
	}
	if (fdp != NULL)
	*fdp = sock;
	else
	close(sock);
	return 0;
	}

	/* Communicate with agent: send request and read reply */
	static int
	ssh_request_reply(int sock, struct sshbuf request, struct sshbuf reply)
	{
	int r;
	size_t l, len;
	char buf[1024];

	/* Get the length of the message, and format it in the buffer. */
	len = sshbuf_len(request);
	POKE_U32(buf, len);

	/* Send the length and then the packet to the agent. */
	if (atomicio(vwrite, sock, buf, 4) != 4 \|\|
	atomicio(vwrite, sock, sshbuf_mutable_ptr(request),
	sshbuf_len(request)) != sshbuf_len(request))
	return SSH_ERR_AGENT_COMMUNICATION;
	/*
	* Wait for response from the agent. First read the length of the
	* response packet.
	*/
	if (atomicio(read, sock, buf, 4) != 4)
	return SSH_ERR_AGENT_COMMUNICATION;

	/* Extract the length, and check it for sanity. */
	len = PEEK_U32(buf);
	if (len > MAX_AGENT_REPLY_LEN)
	return SSH_ERR_INVALID_FORMAT;

	/* Read the rest of the response in to the buffer. */
	sshbuf_reset(reply);
	while (len > 0) {
	l = len;
	if (l > sizeof(buf))
	l = sizeof(buf);
	if (atomicio(read, sock, buf, l) != l)
	return SSH_ERR_AGENT_COMMUNICATION;
	if ((r = sshbuf_put(reply, buf, l)) != 0)
	return r;
	len -= l;
	}
	return 0;
	}

	/*
	* Closes the agent socket if it should be closed (depends on how it was
	* obtained). The argument must have been returned by
	* ssh_get_authentication_socket().
	*/
	void
	ssh_close_authentication_socket(int sock)
	{
	if (getenv(SSH_AUTHSOCKET_ENV_NAME))
	close(sock);
	}

	/* Lock/unlock agent */
	int
	ssh_lock_agent(int sock, int lock, const char *password)
	{
	int r;
	u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK;
	struct sshbuf *msg;

	if ((msg = sshbuf_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;
	if ((r = sshbuf_put_u8(msg, type)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, password)) != 0)
	goto out;
	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
	goto out;
	if ((r = sshbuf_get_u8(msg, &type)) != 0)
	goto out;
	r = decode_reply(type);
	out:
	sshbuf_free(msg);
	return r;
	}


	static int
	deserialise_identity2(struct sshbuf ids, struct sshkey keyp, char *commentp)
	{
	int r;
	char *comment = NULL;
	const u_char *blob;
	size_t blen;

	if ((r = sshbuf_get_string_direct(ids, &blob, &blen)) != 0 \|\|
	(r = sshbuf_get_cstring(ids, &comment, NULL)) != 0)
	goto out;
	if ((r = sshkey_from_blob(blob, blen, keyp)) != 0)
	goto out;
	if (commentp != NULL) {
	*commentp = comment;
	comment = NULL;
	}
	r = 0;
	out:
	free(comment);
	return r;
	}

	/*
	* Fetch list of identities held by the agent.
	*/
	int
	ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp)
	{
	u_char type;
	u_int32_t num, i;
	struct sshbuf *msg;
	struct ssh_identitylist *idl = NULL;
	int r;

	/*
	* Send a message to the agent requesting for a list of the
	* identities it can represent.
	*/
	if ((msg = sshbuf_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;
	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_REQUEST_IDENTITIES)) != 0)
	goto out;

	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
	goto out;

	/* Get message type, and verify that we got a proper answer. */
	if ((r = sshbuf_get_u8(msg, &type)) != 0)
	goto out;
	if (agent_failed(type)) {
	r = SSH_ERR_AGENT_FAILURE;
	goto out;
	} else if (type != SSH2_AGENT_IDENTITIES_ANSWER) {
	r = SSH_ERR_INVALID_FORMAT;
	goto out;
	}

	/* Get the number of entries in the response and check it for sanity. */
	if ((r = sshbuf_get_u32(msg, &num)) != 0)
	goto out;
	if (num > MAX_AGENT_IDENTITIES) {
	r = SSH_ERR_INVALID_FORMAT;
	goto out;
	}
	if (num == 0) {
	r = SSH_ERR_AGENT_NO_IDENTITIES;
	goto out;
	}

	/* Deserialise the response into a list of keys/comments */
	if ((idl = calloc(1, sizeof(*idl))) == NULL \|\|
	(idl->keys = calloc(num, sizeof(*idl->keys))) == NULL \|\|
	(idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) {
	r = SSH_ERR_ALLOC_FAIL;
	goto out;
	}
	for (i = 0; i < num;) {
	if ((r = deserialise_identity2(msg, &(idl->keys[i]),
	&(idl->comments[i]))) != 0) {
	if (r == SSH_ERR_KEY_TYPE_UNKNOWN) {
	/* Gracefully skip unknown key types */
	num--;
	continue;
	} else
	goto out;
	}
	i++;
	}
	idl->nkeys = num;
	*idlp = idl;
	idl = NULL;
	r = 0;
	out:
	sshbuf_free(msg);
	if (idl != NULL)
	ssh_free_identitylist(idl);
	return r;
	}

	void
	ssh_free_identitylist(struct ssh_identitylist *idl)
	{
	size_t i;

	if (idl == NULL)
	return;
	for (i = 0; i < idl->nkeys; i++) {
	if (idl->keys != NULL)
	sshkey_free(idl->keys[i]);
	if (idl->comments != NULL)
	free(idl->comments[i]);
	}
	free(idl);
	}

	/*
	* Sends a challenge (typically from a server via ssh(1)) to the agent,
	* and waits for a response from the agent.
	* Returns true (non-zero) if the agent gave the correct answer, zero
	* otherwise.
	*/


	/* encode signature algorithm in flag bits, so we can keep the msg format */
	static u_int
	agent_encode_alg(const struct sshkey key, const char alg)
	{
	if (alg != NULL && key->type == KEY_RSA) {
	if (strcmp(alg, "rsa-sha2-256") == 0)
	return SSH_AGENT_RSA_SHA2_256;
	else if (strcmp(alg, "rsa-sha2-512") == 0)
	return SSH_AGENT_RSA_SHA2_512;
	}
	return 0;
	}

	/* ask agent to sign data, returns err.h code on error, 0 on success */
	int
	ssh_agent_sign(int sock, const struct sshkey *key,
	u_char *sigp, size_t lenp,
	const u_char data, size_t datalen, const char alg, u_int compat)
	{
	struct sshbuf *msg;
	u_char *sig = NULL, type = 0;
	size_t len = 0;
	u_int flags = 0;
	int r = SSH_ERR_INTERNAL_ERROR;

	*sigp = NULL;
	*lenp = 0;

	if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE)
	return SSH_ERR_INVALID_ARGUMENT;
	if ((msg = sshbuf_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;
	flags \|= agent_encode_alg(key, alg);
	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 \|\|
	(r = sshkey_puts(key, msg)) != 0 \|\|
	(r = sshbuf_put_string(msg, data, datalen)) != 0 \|\|
	(r = sshbuf_put_u32(msg, flags)) != 0)
	goto out;
	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
	goto out;
	if ((r = sshbuf_get_u8(msg, &type)) != 0)
	goto out;
	if (agent_failed(type)) {
	r = SSH_ERR_AGENT_FAILURE;
	goto out;
	} else if (type != SSH2_AGENT_SIGN_RESPONSE) {
	r = SSH_ERR_INVALID_FORMAT;
	goto out;
	}
	if ((r = sshbuf_get_string(msg, &sig, &len)) != 0)
	goto out;
	/* Check what we actually got back from the agent. */
	if ((r = sshkey_check_sigtype(sig, len, alg)) != 0)
	goto out;
	/* success */
	*sigp = sig;
	*lenp = len;
	sig = NULL;
	len = 0;
	r = 0;
	out:
	freezero(sig, len);
	sshbuf_free(msg);
	return r;
	}

	/* Encode key for a message to the agent. */


	static int
	encode_constraints(struct sshbuf *m, u_int life, u_int confirm, u_int maxsign)
	{
	int r;

	if (life != 0) {
	if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 \|\|
	(r = sshbuf_put_u32(m, life)) != 0)
	goto out;
	}
	if (confirm != 0) {
	if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0)
	goto out;
	}
	if (maxsign != 0) {
	if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_MAXSIGN)) != 0 \|\|
	(r = sshbuf_put_u32(m, maxsign)) != 0)
	goto out;
	}
	r = 0;
	out:
	return r;
	}

	/*
	* Adds an identity to the authentication server.
	* This call is intended only for use by ssh-add(1) and like applications.
	*/
	int
	ssh_add_identity_constrained(int sock, const struct sshkey *key,
	const char *comment, u_int life, u_int confirm, u_int maxsign)
	{
	struct sshbuf *msg;
	int r, constrained = (life \|\| confirm \|\| maxsign);
	u_char type;

	if ((msg = sshbuf_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;

	switch (key->type) {
	#ifdef WITH_OPENSSL
	case KEY_RSA:
	case KEY_RSA_CERT:
	case KEY_DSA:
	case KEY_DSA_CERT:
	case KEY_ECDSA:
	case KEY_ECDSA_CERT:
	#endif
	case KEY_ED25519:
	case KEY_ED25519_CERT:
	case KEY_XMSS:
	case KEY_XMSS_CERT:
	type = constrained ?
	SSH2_AGENTC_ADD_ID_CONSTRAINED :
	SSH2_AGENTC_ADD_IDENTITY;
	if ((r = sshbuf_put_u8(msg, type)) != 0 \|\|
	(r = sshkey_private_serialize_maxsign(key, msg, maxsign,
	NULL)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, comment)) != 0)
	goto out;
	break;
	default:
	r = SSH_ERR_INVALID_ARGUMENT;
	goto out;
	}
	if (constrained &&
	(r = encode_constraints(msg, life, confirm, maxsign)) != 0)
	goto out;
	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
	goto out;
	if ((r = sshbuf_get_u8(msg, &type)) != 0)
	goto out;
	r = decode_reply(type);
	out:
	sshbuf_free(msg);
	return r;
	}

	/*
	* Removes an identity from the authentication server.
	* This call is intended only for use by ssh-add(1) and like applications.
	*/
	int
	ssh_remove_identity(int sock, struct sshkey *key)
	{
	struct sshbuf *msg;
	int r;
	u_char type, *blob = NULL;
	size_t blen;

	if ((msg = sshbuf_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;

	if (key->type != KEY_UNSPEC) {
	if ((r = sshkey_to_blob(key, &blob, &blen)) != 0)
	goto out;
	if ((r = sshbuf_put_u8(msg,
	SSH2_AGENTC_REMOVE_IDENTITY)) != 0 \|\|
	(r = sshbuf_put_string(msg, blob, blen)) != 0)
	goto out;
	} else {
	r = SSH_ERR_INVALID_ARGUMENT;
	goto out;
	}
	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
	goto out;
	if ((r = sshbuf_get_u8(msg, &type)) != 0)
	goto out;
	r = decode_reply(type);
	out:
	if (blob != NULL) {
	explicit_bzero(blob, blen);
	free(blob);
	}
	sshbuf_free(msg);
	return r;
	}

	/*
	* Add/remove an token-based identity from the authentication server.
	* This call is intended only for use by ssh-add(1) and like applications.
	*/
	int
	ssh_update_card(int sock, int add, const char reader_id, const char pin,
	u_int life, u_int confirm)
	{
	struct sshbuf *msg;
	int r, constrained = (life \|\| confirm);
	u_char type;

	if (add) {
	type = constrained ?
	SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED :
	SSH_AGENTC_ADD_SMARTCARD_KEY;
	} else
	type = SSH_AGENTC_REMOVE_SMARTCARD_KEY;

	if ((msg = sshbuf_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;
	if ((r = sshbuf_put_u8(msg, type)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, reader_id)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, pin)) != 0)
	goto out;
	if (constrained &&
	(r = encode_constraints(msg, life, confirm, 0)) != 0)
	goto out;
	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
	goto out;
	if ((r = sshbuf_get_u8(msg, &type)) != 0)
	goto out;
	r = decode_reply(type);
	out:
	sshbuf_free(msg);
	return r;
	}

	/*
	* Removes all identities from the agent.
	* This call is intended only for use by ssh-add(1) and like applications.
	*
	* This supports the SSH protocol 1 message to because, when clearing all
	* keys from an agent, we generally want to clear both protocol v1 and v2
	* keys.
	*/
	int
	ssh_remove_all_identities(int sock, int version)
	{
	struct sshbuf *msg;
	u_char type = (version == 1) ?
	SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES :
	SSH2_AGENTC_REMOVE_ALL_IDENTITIES;
	int r;

	if ((msg = sshbuf_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;
	if ((r = sshbuf_put_u8(msg, type)) != 0)
	goto out;
	if ((r = ssh_request_reply(sock, msg, msg)) != 0)
	goto out;
	if ((r = sshbuf_get_u8(msg, &type)) != 0)
	goto out;
	r = decode_reply(type);
	out:
	sshbuf_free(msg);
	return r;
	}