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openssh/ssh-agent.c
djm@openbsd.org a6d7677c4a upstream: Use hostkey parsed from hostbound userauth request 
Require host-bound userauth requests for forwarded SSH connections.

The hostkey parsed from the host-bound userauth request is now checked
against the most recently bound session ID / hostkey on the agent socket
and the signature refused if they do not match.

ok markus@

OpenBSD-Commit-ID: d69877c9a3bd8d1189a5dbdeceefa432044dae02
2021-12-20 09:28:07 +11:00

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/* $OpenBSD: ssh-agent.c,v 1.283 2021/12/19 22:13:55 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>
#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 "compat.h"
#include "log.h"
#include "misc.h"
#include "digest.h"
#include "ssherr.h"
#include "match.h"
#include "msg.h"
#include "ssherr.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
/* 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;
} 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;
/* 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
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;
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, dch->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, dch->hostname, 1,
SSH_ALLOWED_CA_SIGALGS, &reason) != 0) {
debug_f("cert %s / hostname %s rejected: %s",
key->cert->key_id, dch->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->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
* authenicate *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;
}
/* 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 nentries = 0;
debug2_f("entering");
if ((msg = sshbuf_new()) == NULL || (keys = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
TAILQ_FOREACH(id, &idtab->idlist, next) {
/* 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;
char *fp = NULL, *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 (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);
}
}
/* XXX support PIN required FIDO keys */
if ((r = sshkey_sign(id->key, &signature, &slen,
sshbuf_ptr(data), sshbuf_len(data), agent_decode_alg(key, flags),
id->sk_provider, NULL, compat)) != 0) {
error_fr(r, "sshkey_sign");
goto send;
}
/* Success */
ok = 0;
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);
}
/* 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)
{
char *ext_name = NULL;
int r;
struct sshbuf *b = NULL;
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 {
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)
{
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)) != 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) != 0) {
error_f("failed to parse constraints");
sshbuf_reset(e->request);
goto out;
}
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 (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);
}
#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;
Identity *id;
struct dest_constraint *dest_constraints = NULL;
size_t ndest_constraints = 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) != 0) {
error_f("failed to parse constraints");
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++) {
k = keys[i];
if (lookup_identity(k) == NULL) {
id = xcalloc(1, sizeof(Identity));
id->key = k;
keys[i] = NULL; /* transferred */
id->provider = xstrdup(canonical_provider);
if (*comments[i] != '\0') {
id->comment = comments[i];
comments[i] = NULL; /* transferred */
} else {
id->comment = xstrdup(canonical_provider);
}
id->death = death;
id->confirm = confirm;
id->dest_constraints = dest_constraints;
id->ndest_constraints = ndest_constraints;
dest_constraints = NULL; /* transferred */
ndest_constraints = 0;
TAILQ_INSERT_TAIL(&idtab->idlist, id, next);
idtab->nentries++;
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);
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");
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:
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);
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);
}
/*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 allowed_providers] [-t life]\n"
" ssh-agent [-a bind_address] [-E fingerprint_hash] [-P allowed_providers]\n"
" [-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 */
setegid(getgid());
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
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 */
}
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