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ssh-agent.c
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/* $OpenBSD: ssh-agent.c,v 1.310 2025/02/18 08:02:48 djm Exp $ */
/*
* Author: Tatu Ylonen <[email protected]>
* Copyright (c) 1995 Tatu Ylonen <[email protected]>, Espoo, Finland
* All rights reserved
* The authentication agent program.
*
* As far as I am concerned, the code I have written for this software
* can be used freely for any purpose. Any derived versions of this
* software must be clearly marked as such, and if the derived work is
* incompatible with the protocol description in the RFC file, it must be
* called by a name other than "ssh" or "Secure Shell".
*
* Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "includes.h"
#include <sys/types.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/wait.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif
#ifdef HAVE_SYS_UN_H
# include <sys/un.h>
#endif
#include "openbsd-compat/sys-queue.h"
#ifdef WITH_OPENSSL
#include <openssl/evp.h>
#include "openbsd-compat/openssl-compat.h"
#endif
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#ifdef HAVE_PATHS_H
# include <paths.h>
#endif
#ifdef HAVE_POLL_H
# include <poll.h>
#endif
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#ifdef HAVE_UTIL_H
# include <util.h>
#endif
#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "sshbuf.h"
#include "sshkey.h"
#include "authfd.h"
#include "log.h"
#include "misc.h"
#include "digest.h"
#include "ssherr.h"
#include "match.h"
#include "msg.h"
#include "pathnames.h"
#include "ssh-pkcs11.h"
#include "sk-api.h"
#include "myproposal.h"
#ifndef DEFAULT_ALLOWED_PROVIDERS
# define DEFAULT_ALLOWED_PROVIDERS "/usr/lib*/*,/usr/local/lib*/*"
#endif
#ifndef DEFAULT_WEBSAFE_ALLOWLIST
# define DEFAULT_WEBSAFE_ALLOWLIST "ssh:*"
#endif
/* Maximum accepted message length */
#define AGENT_MAX_LEN (256*1024)
/* Maximum bytes to read from client socket */
#define AGENT_RBUF_LEN (4096)
/* Maximum number of recorded session IDs/hostkeys per connection */
#define AGENT_MAX_SESSION_IDS 16
/* Maximum size of session ID */
#define AGENT_MAX_SID_LEN 128
/* Maximum number of destination constraints to accept on a key */
#define AGENT_MAX_DEST_CONSTRAINTS 1024
/* Maximum number of associated certificate constraints to accept on a key */
#define AGENT_MAX_EXT_CERTS 1024
/* XXX store hostkey_sid in a refcounted tree */
typedef enum {
AUTH_UNUSED = 0,
AUTH_SOCKET = 1,
AUTH_CONNECTION = 2,
} sock_type;
struct hostkey_sid {
struct sshkey *key;
struct sshbuf *sid;
int forwarded;
};
typedef struct socket_entry {
int fd;
sock_type type;
struct sshbuf *input;
struct sshbuf *output;
struct sshbuf *request;
size_t nsession_ids;
struct hostkey_sid *session_ids;
int session_bind_attempted;
} SocketEntry;
u_int sockets_alloc = 0;
SocketEntry *sockets = NULL;
typedef struct identity {
TAILQ_ENTRY(identity) next;
struct sshkey *key;
char *comment;
char *provider;
time_t death;
u_int confirm;
char *sk_provider;
struct dest_constraint *dest_constraints;
size_t ndest_constraints;
} Identity;
struct idtable {
int nentries;
TAILQ_HEAD(idqueue, identity) idlist;
};
/* private key table */
struct idtable *idtab;
int max_fd = 0;
/* pid of shell == parent of agent */
pid_t parent_pid = -1;
time_t parent_alive_interval = 0;
static sig_atomic_t signalled_exit;
static sig_atomic_t signalled_keydrop;
/* pid of process for which cleanup_socket is applicable */
pid_t cleanup_pid = 0;
/* pathname and directory for AUTH_SOCKET */
char socket_name[PATH_MAX];
char socket_dir[PATH_MAX];
/* Pattern-list of allowed PKCS#11/Security key paths */
static char *allowed_providers;
/*
* Allows PKCS11 providers or SK keys that use non-internal providers to
* be added over a remote connection (identified by [email protected]).
*/
static int remote_add_provider;
/* locking */
#define LOCK_SIZE 32
#define LOCK_SALT_SIZE 16
#define LOCK_ROUNDS 1
int locked = 0;
u_char lock_pwhash[LOCK_SIZE];
u_char lock_salt[LOCK_SALT_SIZE];
extern char *__progname;
/* Default lifetime in seconds (0 == forever) */
static int lifetime = 0;
static int fingerprint_hash = SSH_FP_HASH_DEFAULT;
/* Refuse signing of non-SSH messages for web-origin FIDO keys */
static int restrict_websafe = 1;
static char *websafe_allowlist;
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);
}
#ifdef ENABLE_PKCS11
static void
dup_dest_constraint_hop(const struct dest_constraint_hop *dch,
struct dest_constraint_hop *out)
{
u_int i;
int r;
out->user = dch->user == NULL ? NULL : xstrdup(dch->user);
out->hostname = dch->hostname == NULL ? NULL : xstrdup(dch->hostname);
out->is_ca = dch->is_ca;
out->nkeys = dch->nkeys;
out->keys = out->nkeys == 0 ? NULL :
xcalloc(out->nkeys, sizeof(*out->keys));
out->key_is_ca = out->nkeys == 0 ? NULL :
xcalloc(out->nkeys, sizeof(*out->key_is_ca));
for (i = 0; i < dch->nkeys; i++) {
if (dch->keys[i] != NULL &&
(r = sshkey_from_private(dch->keys[i],
&(out->keys[i]))) != 0)
fatal_fr(r, "copy key");
out->key_is_ca[i] = dch->key_is_ca[i];
}
}
static struct dest_constraint *
dup_dest_constraints(const struct dest_constraint *dcs, size_t ndcs)
{
size_t i;
struct dest_constraint *ret;
if (ndcs == 0)
return NULL;
ret = xcalloc(ndcs, sizeof(*ret));
for (i = 0; i < ndcs; i++) {
dup_dest_constraint_hop(&dcs[i].from, &ret[i].from);
dup_dest_constraint_hop(&dcs[i].to, &ret[i].to);
}
return ret;
}
#endif /* ENABLE_PKCS11 */
#ifdef DEBUG_CONSTRAINTS
static void
dump_dest_constraint_hop(const struct dest_constraint_hop *dch)
{
u_int i;
char *fp;
debug_f("user %s hostname %s is_ca %d nkeys %u",
dch->user == NULL ? "(null)" : dch->user,
dch->hostname == NULL ? "(null)" : dch->hostname,
dch->is_ca, dch->nkeys);
for (i = 0; i < dch->nkeys; i++) {
fp = NULL;
if (dch->keys[i] != NULL &&
(fp = sshkey_fingerprint(dch->keys[i],
SSH_FP_HASH_DEFAULT, SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
debug_f("key %u/%u: %s%s%s key_is_ca %d", i, dch->nkeys,
dch->keys[i] == NULL ? "" : sshkey_ssh_name(dch->keys[i]),
dch->keys[i] == NULL ? "" : " ",
dch->keys[i] == NULL ? "none" : fp,
dch->key_is_ca[i]);
free(fp);
}
}
#endif /* DEBUG_CONSTRAINTS */
static void
dump_dest_constraints(const char *context,
const struct dest_constraint *dcs, size_t ndcs)
{
#ifdef DEBUG_CONSTRAINTS
size_t i;
debug_f("%s: %zu constraints", context, ndcs);
for (i = 0; i < ndcs; i++) {
debug_f("constraint %zu / %zu: from: ", i, ndcs);
dump_dest_constraint_hop(&dcs[i].from);
debug_f("constraint %zu / %zu: to: ", i, ndcs);
dump_dest_constraint_hop(&dcs[i].to);
}
debug_f("done for %s", context);
#endif /* DEBUG_CONSTRAINTS */
}
static void
free_identity(Identity *id)
{
sshkey_free(id->key);
free(id->provider);
free(id->comment);
free(id->sk_provider);
free_dest_constraints(id->dest_constraints, id->ndest_constraints);
free(id);
}
/*
* Match 'key' against the key/CA list in a destination constraint hop
* Returns 0 on success or -1 otherwise.
*/
static int
match_key_hop(const char *tag, const struct sshkey *key,
const struct dest_constraint_hop *dch)
{
const char *reason = NULL;
const char *hostname = dch->hostname ? dch->hostname : "(ORIGIN)";
u_int i;
char *fp;
if (key == NULL)
return -1;
/* XXX logspam */
if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
debug3_f("%s: entering hostname %s, requested key %s %s, %u keys avail",
tag, hostname, sshkey_type(key), fp, dch->nkeys);
free(fp);
for (i = 0; i < dch->nkeys; i++) {
if (dch->keys[i] == NULL)
return -1;
/* XXX logspam */
if ((fp = sshkey_fingerprint(dch->keys[i], SSH_FP_HASH_DEFAULT,
SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
debug3_f("%s: key %u: %s%s %s", tag, i,
dch->key_is_ca[i] ? "CA " : "",
sshkey_type(dch->keys[i]), fp);
free(fp);
if (!sshkey_is_cert(key)) {
/* plain key */
if (dch->key_is_ca[i] ||
!sshkey_equal(key, dch->keys[i]))
continue;
return 0;
}
/* certificate */
if (!dch->key_is_ca[i])
continue;
if (key->cert == NULL || key->cert->signature_key == NULL)
return -1; /* shouldn't happen */
if (!sshkey_equal(key->cert->signature_key, dch->keys[i]))
continue;
if (sshkey_cert_check_host(key, hostname, 1,
SSH_ALLOWED_CA_SIGALGS, &reason) != 0) {
debug_f("cert %s / hostname %s rejected: %s",
key->cert->key_id, hostname, reason);
continue;
}
return 0;
}
return -1;
}
/* Check destination constraints on an identity against the hostkey/user */
static int
permitted_by_dest_constraints(const struct sshkey *fromkey,
const struct sshkey *tokey, Identity *id, const char *user,
const char **hostnamep)
{
size_t i;
struct dest_constraint *d;
if (hostnamep != NULL)
*hostnamep = NULL;
for (i = 0; i < id->ndest_constraints; i++) {
d = id->dest_constraints + i;
/* XXX remove logspam */
debug2_f("constraint %zu %s%s%s (%u keys) > %s%s%s (%u keys)",
i, d->from.user ? d->from.user : "",
d->from.user ? "@" : "",
d->from.hostname ? d->from.hostname : "(ORIGIN)",
d->from.nkeys,
d->to.user ? d->to.user : "", d->to.user ? "@" : "",
d->to.hostname ? d->to.hostname : "(ANY)", d->to.nkeys);
/* Match 'from' key */
if (fromkey == NULL) {
/* We are matching the first hop */
if (d->from.hostname != NULL || d->from.nkeys != 0)
continue;
} else if (match_key_hop("from", fromkey, &d->from) != 0)
continue;
/* Match 'to' key */
if (tokey != NULL && match_key_hop("to", tokey, &d->to) != 0)
continue;
/* Match user if specified */
if (d->to.user != NULL && user != NULL &&
!match_pattern(user, d->to.user))
continue;
/* successfully matched this constraint */
if (hostnamep != NULL)
*hostnamep = d->to.hostname;
debug2_f("allowed for hostname %s",
d->to.hostname == NULL ? "*" : d->to.hostname);
return 0;
}
/* no match */
debug2_f("%s identity \"%s\" not permitted for this destination",
sshkey_type(id->key), id->comment);
return -1;
}
/*
* Check whether hostkeys on a SocketEntry and the optionally specified user
* are permitted by the destination constraints on the Identity.
* Returns 0 on success or -1 otherwise.
*/
static int
identity_permitted(Identity *id, SocketEntry *e, char *user,
const char **forward_hostnamep, const char **last_hostnamep)
{
size_t i;
const char **hp;
struct hostkey_sid *hks;
const struct sshkey *fromkey = NULL;
const char *test_user;
char *fp1, *fp2;
/* XXX remove logspam */
debug3_f("entering: key %s comment \"%s\", %zu socket bindings, "
"%zu constraints", sshkey_type(id->key), id->comment,
e->nsession_ids, id->ndest_constraints);
if (id->ndest_constraints == 0)
return 0; /* unconstrained */
if (e->session_bind_attempted && e->nsession_ids == 0) {
error_f("previous session bind failed on socket");
return -1;
}
if (e->nsession_ids == 0)
return 0; /* local use */
/*
* Walk through the hops recorded by session_id and try to find a
* constraint that satisfies each.
*/
for (i = 0; i < e->nsession_ids; i++) {
hks = e->session_ids + i;
if (hks->key == NULL)
fatal_f("internal error: no bound key");
/* XXX remove logspam */
fp1 = fp2 = NULL;
if (fromkey != NULL &&
(fp1 = sshkey_fingerprint(fromkey, SSH_FP_HASH_DEFAULT,
SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
if ((fp2 = sshkey_fingerprint(hks->key, SSH_FP_HASH_DEFAULT,
SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
debug3_f("socketentry fd=%d, entry %zu %s, "
"from hostkey %s %s to user %s hostkey %s %s",
e->fd, i, hks->forwarded ? "FORWARD" : "AUTH",
fromkey ? sshkey_type(fromkey) : "(ORIGIN)",
fromkey ? fp1 : "", user ? user : "(ANY)",
sshkey_type(hks->key), fp2);
free(fp1);
free(fp2);
/*
* Record the hostnames for the initial forwarding and
* the final destination.
*/
hp = NULL;
if (i == e->nsession_ids - 1)
hp = last_hostnamep;
else if (i == 0)
hp = forward_hostnamep;
/* Special handling for final recorded binding */
test_user = NULL;
if (i == e->nsession_ids - 1) {
/* Can only check user at final hop */
test_user = user;
/*
* user is only presented for signature requests.
* If this is the case, make sure last binding is not
* for a forwarding.
*/
if (hks->forwarded && user != NULL) {
error_f("tried to sign on forwarding hop");
return -1;
}
} else if (!hks->forwarded) {
error_f("tried to forward though signing bind");
return -1;
}
if (permitted_by_dest_constraints(fromkey, hks->key, id,
test_user, hp) != 0)
return -1;
fromkey = hks->key;
}
/*
* Another special case: if the last bound session ID was for a
* forwarding, and this function is not being called to check a sign
* request (i.e. no 'user' supplied), then only permit the key if
* there is a permission that would allow it to be used at another
* destination. This hides keys that are allowed to be used to
* authenticate *to* a host but not permitted for *use* beyond it.
*/
hks = &e->session_ids[e->nsession_ids - 1];
if (hks->forwarded && user == NULL &&
permitted_by_dest_constraints(hks->key, NULL, id,
NULL, NULL) != 0) {
debug3_f("key permitted at host but not after");
return -1;
}
/* success */
return 0;
}
static int
socket_is_remote(SocketEntry *e)
{
return e->session_bind_attempted || (e->nsession_ids != 0);
}
/* return matching private key for given public key */
static Identity *
lookup_identity(struct sshkey *key)
{
Identity *id;
TAILQ_FOREACH(id, &idtab->idlist, next) {
if (sshkey_equal(key, id->key))
return (id);
}
return (NULL);
}
/* Check confirmation of keysign request */
static int
confirm_key(Identity *id, const char *extra)
{
char *p;
int ret = -1;
p = sshkey_fingerprint(id->key, fingerprint_hash, SSH_FP_DEFAULT);
if (p != NULL &&
ask_permission("Allow use of key %s?\nKey fingerprint %s.%s%s",
id->comment, p,
extra == NULL ? "" : "\n", extra == NULL ? "" : extra))
ret = 0;
free(p);
return (ret);
}
static void
send_status(SocketEntry *e, int success)
{
int r;
if ((r = sshbuf_put_u32(e->output, 1)) != 0 ||
(r = sshbuf_put_u8(e->output, success ?
SSH_AGENT_SUCCESS : SSH_AGENT_FAILURE)) != 0)
fatal_fr(r, "compose");
}
/* send list of supported public keys to 'client' */
static void
process_request_identities(SocketEntry *e)
{
Identity *id;
struct sshbuf *msg, *keys;
int r;
u_int i = 0, nentries = 0;
char *fp;
debug2_f("entering");
if ((msg = sshbuf_new()) == NULL || (keys = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
TAILQ_FOREACH(id, &idtab->idlist, next) {
if ((fp = sshkey_fingerprint(id->key, SSH_FP_HASH_DEFAULT,
SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
debug_f("key %u / %u: %s %s", i++, idtab->nentries,
sshkey_ssh_name(id->key), fp);
dump_dest_constraints(__func__,
id->dest_constraints, id->ndest_constraints);
free(fp);
/* identity not visible, don't include in response */
if (identity_permitted(id, e, NULL, NULL, NULL) != 0)
continue;
if ((r = sshkey_puts_opts(id->key, keys,
SSHKEY_SERIALIZE_INFO)) != 0 ||
(r = sshbuf_put_cstring(keys, id->comment)) != 0) {
error_fr(r, "compose key/comment");
continue;
}
nentries++;
}
debug2_f("replying with %u allowed of %u available keys",
nentries, idtab->nentries);
if ((r = sshbuf_put_u8(msg, SSH2_AGENT_IDENTITIES_ANSWER)) != 0 ||
(r = sshbuf_put_u32(msg, nentries)) != 0 ||
(r = sshbuf_putb(msg, keys)) != 0)
fatal_fr(r, "compose");
if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
fatal_fr(r, "enqueue");
sshbuf_free(msg);
sshbuf_free(keys);
}
static char *
agent_decode_alg(struct sshkey *key, u_int flags)
{
if (key->type == KEY_RSA) {
if (flags & SSH_AGENT_RSA_SHA2_256)
return "rsa-sha2-256";
else if (flags & SSH_AGENT_RSA_SHA2_512)
return "rsa-sha2-512";
} else if (key->type == KEY_RSA_CERT) {
if (flags & SSH_AGENT_RSA_SHA2_256)
return "[email protected]";
else if (flags & SSH_AGENT_RSA_SHA2_512)
return "[email protected]";
}
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 ((r = sshkey_froms(b, &hostkey)) != 0)
goto out;
} else if (strcmp(method, "publickey") != 0) {
r = SSH_ERR_INVALID_FORMAT;
goto out;
}
if (sshbuf_len(b) != 0) {
r = SSH_ERR_INVALID_FORMAT;
goto out;
}
/* success */
r = 0;
debug3_f("well formed userauth");
if (userp != NULL) {
*userp = user;
user = NULL;
}
if (sess_idp != NULL) {
*sess_idp = sess_id;
sess_id = NULL;
}
if (hostkeyp != NULL) {
*hostkeyp = hostkey;
hostkey = NULL;
}
out:
sshbuf_free(b);
sshbuf_free(sess_id);
free(user);
free(service);
free(method);
free(pkalg);
sshkey_free(mkey);
sshkey_free(hostkey);
return r;
}
/*
* Attempt to parse the contents of a buffer as a SSHSIG signature request.
* Note: does not modify buffer.
*/
static int
parse_sshsig_request(struct sshbuf *msg)
{
int r;
struct sshbuf *b;
if ((b = sshbuf_fromb(msg)) == NULL)
fatal_f("sshbuf_fromb");
if ((r = sshbuf_cmp(b, 0, "SSHSIG", 6)) != 0 ||
(r = sshbuf_consume(b, 6)) != 0 ||
(r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* namespace */
(r = sshbuf_get_string_direct(b, NULL, NULL)) != 0 || /* reserved */
(r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* hashalg */
(r = sshbuf_get_string_direct(b, NULL, NULL)) != 0) /* H(msg) */
goto out;
if (sshbuf_len(b) != 0) {
r = SSH_ERR_INVALID_FORMAT;
goto out;
}
/* success */
r = 0;
out:
sshbuf_free(b);
return r;
}
/*
* This function inspects a message to be signed by a FIDO key that has a
* web-like application string (i.e. one that does not begin with "ssh:".
* It checks that the message is one of those expected for SSH operations
* (pubkey userauth, sshsig, CA key signing) to exclude signing challenges
* for the web.
*/
static int
check_websafe_message_contents(struct sshkey *key, struct sshbuf *data)
{
if (parse_userauth_request(data, key, NULL, NULL, NULL) == 0) {
debug_f("signed data matches public key userauth request");
return 1;
}
if (parse_sshsig_request(data) == 0) {
debug_f("signed data matches SSHSIG signature request");
return 1;
}
/* XXX check CA signature operation */
error("web-origin key attempting to sign non-SSH message");
return 0;
}
static int
buf_equal(const struct sshbuf *a, const struct sshbuf *b)
{
if (sshbuf_ptr(a) == NULL || sshbuf_ptr(b) == NULL)
return SSH_ERR_INVALID_ARGUMENT;
if (sshbuf_len(a) != sshbuf_len(b))
return SSH_ERR_INVALID_FORMAT;
if (timingsafe_bcmp(sshbuf_ptr(a), sshbuf_ptr(b), sshbuf_len(a)) != 0)
return SSH_ERR_INVALID_FORMAT;
return 0;
}
/* ssh2 only */
static void
process_sign_request2(SocketEntry *e)
{
u_char *signature = NULL;
size_t slen = 0;
u_int compat = 0, flags;
int r, ok = -1, retried = 0;
char *fp = NULL, *pin = NULL, *prompt = NULL;
char *user = NULL, *sig_dest = NULL;
const char *fwd_host = NULL, *dest_host = NULL;
struct sshbuf *msg = NULL, *data = NULL, *sid = NULL;
struct sshkey *key = NULL, *hostkey = NULL;
struct identity *id;
struct notifier_ctx *notifier = NULL;
debug_f("entering");
if ((msg = sshbuf_new()) == NULL || (data = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
if ((r = sshkey_froms(e->request, &key)) != 0 ||
(r = sshbuf_get_stringb(e->request, data)) != 0 ||
(r = sshbuf_get_u32(e->request, &flags)) != 0) {
error_fr(r, "parse");
goto send;
}
if ((id = lookup_identity(key)) == NULL) {
verbose_f("%s key not found", sshkey_type(key));
goto send;
}
if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
if (id->ndest_constraints != 0) {
if (e->nsession_ids == 0) {
logit_f("refusing use of destination-constrained key "
"to sign on unbound connection");
goto send;
}
if (parse_userauth_request(data, key, &user, &sid,
&hostkey) != 0) {
logit_f("refusing use of destination-constrained key "
"to sign an unidentified signature");
goto send;
}
/* XXX logspam */
debug_f("user=%s", user);
if (identity_permitted(id, e, user, &fwd_host, &dest_host) != 0)
goto send;
/* XXX display fwd_host/dest_host in askpass UI */
/*
* Ensure that the session ID is the most recent one
* registered on the socket - it should have been bound by
* ssh immediately before userauth.
*/
if (buf_equal(sid,
e->session_ids[e->nsession_ids - 1].sid) != 0) {
error_f("unexpected session ID (%zu listed) on "
"signature request for target user %s with "
"key %s %s", e->nsession_ids, user,
sshkey_type(id->key), fp);
goto send;
}
/*
* Ensure that the hostkey embedded in the signature matches
* the one most recently bound to the socket. An exception is
* made for the initial forwarding hop.
*/
if (e->nsession_ids > 1 && hostkey == NULL) {
error_f("refusing use of destination-constrained key: "
"no hostkey recorded in signature for forwarded "
"connection");
goto send;
}
if (hostkey != NULL && !sshkey_equal(hostkey,
e->session_ids[e->nsession_ids - 1].key)) {
error_f("refusing use of destination-constrained key: "
"mismatch between hostkey in request and most "
"recently bound session");
goto send;
}
xasprintf(&sig_dest, "public key authentication request for "
"user \"%s\" to listed host", user);
}
if (id->confirm && confirm_key(id, sig_dest) != 0) {
verbose_f("user refused key");
goto send;
}
if (sshkey_is_sk(id->key)) {
if (restrict_websafe &&
match_pattern_list(id->key->sk_application,
websafe_allowlist, 0) != 1 &&
!check_websafe_message_contents(key, data)) {
/* error already logged */
goto send;
}
if (id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD) {
notifier = notify_start(0,
"Confirm user presence for key %s %s%s%s",
sshkey_type(id->key), fp,
sig_dest == NULL ? "" : "\n",
sig_dest == NULL ? "" : sig_dest);
}
}
retry_pin:
if ((r = sshkey_sign(id->key, &signature, &slen,
sshbuf_ptr(data), sshbuf_len(data), agent_decode_alg(key, flags),
id->sk_provider, pin, compat)) != 0) {
debug_fr(r, "sshkey_sign");
if (pin == NULL && !retried && sshkey_is_sk(id->key) &&
r == SSH_ERR_KEY_WRONG_PASSPHRASE) {
notify_complete(notifier, NULL);
notifier = NULL;
/* XXX include sig_dest */
xasprintf(&prompt, "Enter PIN%sfor %s key %s: ",
(id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD) ?
" and confirm user presence " : " ",
sshkey_type(id->key), fp);
pin = read_passphrase(prompt, RP_USE_ASKPASS);
retried = 1;
goto retry_pin;
}
error_fr(r, "sshkey_sign");
goto send;
}
/* Success */
ok = 0;
debug_f("good signature");
send:
notify_complete(notifier, "User presence confirmed");
if (ok == 0) {
if ((r = sshbuf_put_u8(msg, SSH2_AGENT_SIGN_RESPONSE)) != 0 ||
(r = sshbuf_put_string(msg, signature, slen)) != 0)
fatal_fr(r, "compose");
} else if ((r = sshbuf_put_u8(msg, SSH_AGENT_FAILURE)) != 0)
fatal_fr(r, "compose failure");
if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
fatal_fr(r, "enqueue");
sshbuf_free(sid);
sshbuf_free(data);
sshbuf_free(msg);
sshkey_free(key);
sshkey_free(hostkey);
free(fp);
free(signature);
free(sig_dest);
free(user);
free(prompt);
if (pin != NULL)
freezero(pin, strlen(pin));
}
/* shared */
static void
process_remove_identity(SocketEntry *e)
{