/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, struct sshkey *host_key)
{
int flags = 0;
char *fp;
fp = sshkey_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
debug("Server host key: %s %s", sshkey_type(host_key), fp);
xfree(fp);
/* XXX certs are not yet supported for DNS */
if (!sshkey_is_cert(host_key) && options.verify_host_key_dns &&
verify_host_key_dns(host, hostaddr, host_key, &flags) == 0) {
if (flags & DNS_VERIFY_FOUND) {
if (options.verify_host_key_dns == 1 &&
flags & DNS_VERIFY_MATCH &&
flags & DNS_VERIFY_SECURE)
return 0;
if (flags & DNS_VERIFY_MATCH) {
matching_host_key_dns = 1;
} else {
warn_changed_key(host_key);
error("Update the SSHFP RR in DNS with the new "
"host key to get rid of this message.");
}
}
}
return check_host_key(host, hostaddr, options.port, host_key, RDRW,
options.user_hostfiles, options.num_user_hostfiles,
options.system_hostfiles, options.num_system_hostfiles);
}
/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
{
int flags = 0;
char *fp;
Key *plain = NULL;
fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
debug("Server host key: %s %s", key_type(host_key), fp);
free(fp);
if (options.verify_host_key_dns) {
/*
* XXX certs are not yet supported for DNS, so downgrade
* them and try the plain key.
*/
plain = key_from_private(host_key);
if (key_is_cert(plain))
key_drop_cert(plain);
if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
if (flags & DNS_VERIFY_FOUND) {
if (options.verify_host_key_dns == 1 &&
flags & DNS_VERIFY_MATCH &&
flags & DNS_VERIFY_SECURE) {
key_free(plain);
return 0;
}
if (flags & DNS_VERIFY_MATCH) {
matching_host_key_dns = 1;
} else {
warn_changed_key(plain);
error("Update the SSHFP RR in DNS "
"with the new host key to get rid "
"of this message.");
}
}
}
key_free(plain);
}
return check_host_key(host, hostaddr, options.port, host_key, RDRW,
options.user_hostfiles, options.num_user_hostfiles,
options.system_hostfiles, options.num_system_hostfiles);
}
static int
check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
Key *host_key, int readonly,
char **user_hostfiles, u_int num_user_hostfiles,
char **system_hostfiles, u_int num_system_hostfiles)
{
HostStatus host_status;
HostStatus ip_status;
Key *raw_key = NULL;
char *ip = NULL, *host = NULL;
char hostline[1000], *hostp, *fp, *ra;
char msg[1024];
const char *type;
const struct hostkey_entry *host_found, *ip_found;
int len, cancelled_forwarding = 0;
int local = sockaddr_is_local(hostaddr);
int r, want_cert = key_is_cert(host_key), host_ip_differ = 0;
int hostkey_trusted = 0; /* Known or explicitly accepted by user */
struct hostkeys *host_hostkeys, *ip_hostkeys;
u_int i;
/*
* Force accepting of the host key for loopback/localhost. The
* problem is that if the home directory is NFS-mounted to multiple
* machines, localhost will refer to a different machine in each of
* them, and the user will get bogus HOST_CHANGED warnings. This
* essentially disables host authentication for localhost; however,
* this is probably not a real problem.
*/
if (options.no_host_authentication_for_localhost == 1 && local &&
options.host_key_alias == NULL) {
debug("Forcing accepting of host key for "
"loopback/localhost.");
return 0;
}
/*
* Prepare the hostname and address strings used for hostkey lookup.
* In some cases, these will have a port number appended.
*/
get_hostfile_hostname_ipaddr(hostname, hostaddr, port, &host, &ip);
/*
* Turn off check_host_ip if the connection is to localhost, via proxy
* command or if we don't have a hostname to compare with
*/
if (options.check_host_ip && (local ||
strcmp(hostname, ip) == 0 || options.proxy_command != NULL))
options.check_host_ip = 0;
host_hostkeys = init_hostkeys();
for (i = 0; i < num_user_hostfiles; i++)
load_hostkeys(host_hostkeys, host, user_hostfiles[i]);
for (i = 0; i < num_system_hostfiles; i++)
load_hostkeys(host_hostkeys, host, system_hostfiles[i]);
ip_hostkeys = NULL;
if (!want_cert && options.check_host_ip) {
ip_hostkeys = init_hostkeys();
for (i = 0; i < num_user_hostfiles; i++)
load_hostkeys(ip_hostkeys, ip, user_hostfiles[i]);
for (i = 0; i < num_system_hostfiles; i++)
load_hostkeys(ip_hostkeys, ip, system_hostfiles[i]);
}
retry:
/* Reload these as they may have changed on cert->key downgrade */
want_cert = key_is_cert(host_key);
type = key_type(host_key);
/*
* Check if the host key is present in the user's list of known
* hosts or in the systemwide list.
*/
host_status = check_key_in_hostkeys(host_hostkeys, host_key,
&host_found);
/*
* Also perform check for the ip address, skip the check if we are
* localhost, looking for a certificate, or the hostname was an ip
* address to begin with.
*/
if (!want_cert && ip_hostkeys != NULL) {
ip_status = check_key_in_hostkeys(ip_hostkeys, host_key,
&ip_found);
if (host_status == HOST_CHANGED &&
(ip_status != HOST_CHANGED ||
(ip_found != NULL &&
!key_equal(ip_found->key, host_found->key))))
host_ip_differ = 1;
} else
ip_status = host_status;
switch (host_status) {
case HOST_OK:
/* The host is known and the key matches. */
debug("Host '%.200s' is known and matches the %s host %s.",
host, type, want_cert ? "certificate" : "key");
debug("Found %s in %s:%lu", want_cert ? "CA key" : "key",
host_found->file, host_found->line);
if (want_cert && !check_host_cert(hostname, host_key))
goto fail;
if (options.check_host_ip && ip_status == HOST_NEW) {
if (readonly || want_cert)
logit("%s host key for IP address "
"'%.128s' not in list of known hosts.",
type, ip);
else if (!add_host_to_hostfile(user_hostfiles[0], ip,
host_key, options.hash_known_hosts))
logit("Failed to add the %s host key for IP "
"address '%.128s' to the list of known "
"hosts (%.500s).", type, ip,
user_hostfiles[0]);
else
logit("Warning: Permanently added the %s host "
"key for IP address '%.128s' to the list "
"of known hosts.", type, ip);
} else if (options.visual_host_key) {
fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT);
ra = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_RANDOMART);
if (fp == NULL || ra == NULL)
fatal("%s: sshkey_fingerprint fail", __func__);
logit("Host key fingerprint is %s\n%s\n", fp, ra);
free(ra);
free(fp);
}
hostkey_trusted = 1;
break;
case HOST_NEW:
if (options.host_key_alias == NULL && port != 0 &&
port != SSH_DEFAULT_PORT) {
debug("checking without port identifier");
if (check_host_key(hostname, hostaddr, 0, host_key,
ROQUIET, user_hostfiles, num_user_hostfiles,
system_hostfiles, num_system_hostfiles) == 0) {
debug("found matching key w/out port");
break;
}
}
if (readonly || want_cert)
goto fail;
/* The host is new. */
if (options.strict_host_key_checking == 1) {
/*
* User has requested strict host key checking. We
* will not add the host key automatically. The only
* alternative left is to abort.
*/
error("No %s host key is known for %.200s and you "
"have requested strict checking.", type, host);
goto fail;
} else if (options.strict_host_key_checking == 2) {
char msg1[1024], msg2[1024];
if (show_other_keys(host_hostkeys, host_key))
snprintf(msg1, sizeof(msg1),
"\nbut keys of different type are already"
" known for this host.");
else
snprintf(msg1, sizeof(msg1), ".");
/* The default */
fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT);
ra = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_RANDOMART);
if (fp == NULL || ra == NULL)
fatal("%s: sshkey_fingerprint fail", __func__);
msg2[0] = '\0';
if (options.verify_host_key_dns) {
if (matching_host_key_dns)
snprintf(msg2, sizeof(msg2),
"Matching host key fingerprint"
" found in DNS.\n");
else
snprintf(msg2, sizeof(msg2),
"No matching host key fingerprint"
" found in DNS.\n");
}
snprintf(msg, sizeof(msg),
"The authenticity of host '%.200s (%s)' can't be "
"established%s\n"
"%s key fingerprint is %s.%s%s\n%s"
"Are you sure you want to continue connecting "
"(yes/no)? ",
host, ip, msg1, type, fp,
options.visual_host_key ? "\n" : "",
options.visual_host_key ? ra : "",
msg2);
free(ra);
free(fp);
if (!confirm(msg))
goto fail;
hostkey_trusted = 1; /* user explicitly confirmed */
}
/*
* If not in strict mode, add the key automatically to the
* local known_hosts file.
*/
if (options.check_host_ip && ip_status == HOST_NEW) {
snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
hostp = hostline;
if (options.hash_known_hosts) {
/* Add hash of host and IP separately */
r = add_host_to_hostfile(user_hostfiles[0],
host, host_key, options.hash_known_hosts) &&
add_host_to_hostfile(user_hostfiles[0], ip,
host_key, options.hash_known_hosts);
} else {
/* Add unhashed "host,ip" */
r = add_host_to_hostfile(user_hostfiles[0],
hostline, host_key,
options.hash_known_hosts);
}
} else {
r = add_host_to_hostfile(user_hostfiles[0], host,
host_key, options.hash_known_hosts);
hostp = host;
}
if (!r)
logit("Failed to add the host to the list of known "
"hosts (%.500s).", user_hostfiles[0]);
else
logit("Warning: Permanently added '%.200s' (%s) to the "
"list of known hosts.", hostp, type);
break;
case HOST_REVOKED:
error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
error("@ WARNING: REVOKED HOST KEY DETECTED! @");
error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
error("The %s host key for %s is marked as revoked.", type, host);
error("This could mean that a stolen key is being used to");
error("impersonate this host.");
/*
* If strict host key checking is in use, the user will have
* to edit the key manually and we can only abort.
*/
if (options.strict_host_key_checking) {
error("%s host key for %.200s was revoked and you have "
"requested strict checking.", type, host);
goto fail;
}
goto continue_unsafe;
case HOST_CHANGED:
if (want_cert) {
/*
* This is only a debug() since it is valid to have
* CAs with wildcard DNS matches that don't match
* all hosts that one might visit.
*/
debug("Host certificate authority does not "
"match %s in %s:%lu", CA_MARKER,
host_found->file, host_found->line);
goto fail;
}
if (readonly == ROQUIET)
goto fail;
if (options.check_host_ip && host_ip_differ) {
char *key_msg;
if (ip_status == HOST_NEW)
key_msg = "is unknown";
else if (ip_status == HOST_OK)
key_msg = "is unchanged";
else
key_msg = "has a different value";
error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
error("The %s host key for %s has changed,", type, host);
error("and the key for the corresponding IP address %s", ip);
error("%s. This could either mean that", key_msg);
error("DNS SPOOFING is happening or the IP address for the host");
error("and its host key have changed at the same time.");
if (ip_status != HOST_NEW)
error("Offending key for IP in %s:%lu",
ip_found->file, ip_found->line);
}
/* The host key has changed. */
warn_changed_key(host_key);
error("Add correct host key in %.100s to get rid of this message.",
user_hostfiles[0]);
error("Offending %s key in %s:%lu", key_type(host_found->key),
host_found->file, host_found->line);
/*
* If strict host key checking is in use, the user will have
* to edit the key manually and we can only abort.
*/
if (options.strict_host_key_checking) {
error("%s host key for %.200s has changed and you have "
"requested strict checking.", type, host);
goto fail;
}
continue_unsafe:
/*
* If strict host key checking has not been requested, allow
* the connection but without MITM-able authentication or
* forwarding.
*/
if (options.password_authentication) {
error("Password authentication is disabled to avoid "
"man-in-the-middle attacks.");
options.password_authentication = 0;
cancelled_forwarding = 1;
}
if (options.kbd_interactive_authentication) {
error("Keyboard-interactive authentication is disabled"
" to avoid man-in-the-middle attacks.");
options.kbd_interactive_authentication = 0;
options.challenge_response_authentication = 0;
cancelled_forwarding = 1;
}
if (options.challenge_response_authentication) {
error("Challenge/response authentication is disabled"
" to avoid man-in-the-middle attacks.");
options.challenge_response_authentication = 0;
cancelled_forwarding = 1;
}
if (options.forward_agent) {
error("Agent forwarding is disabled to avoid "
"man-in-the-middle attacks.");
options.forward_agent = 0;
cancelled_forwarding = 1;
}
if (options.forward_x11) {
error("X11 forwarding is disabled to avoid "
"man-in-the-middle attacks.");
options.forward_x11 = 0;
cancelled_forwarding = 1;
}
if (options.num_local_forwards > 0 ||
options.num_remote_forwards > 0) {
error("Port forwarding is disabled to avoid "
"man-in-the-middle attacks.");
options.num_local_forwards =
options.num_remote_forwards = 0;
cancelled_forwarding = 1;
}
if (options.tun_open != SSH_TUNMODE_NO) {
error("Tunnel forwarding is disabled to avoid "
"man-in-the-middle attacks.");
options.tun_open = SSH_TUNMODE_NO;
cancelled_forwarding = 1;
}
if (options.exit_on_forward_failure && cancelled_forwarding)
fatal("Error: forwarding disabled due to host key "
"check failure");
/*
* XXX Should permit the user to change to use the new id.
* This could be done by converting the host key to an
* identifying sentence, tell that the host identifies itself
* by that sentence, and ask the user if he/she wishes to
* accept the authentication.
*/
break;
case HOST_FOUND:
fatal("internal error");
break;
}
if (options.check_host_ip && host_status != HOST_CHANGED &&
ip_status == HOST_CHANGED) {
snprintf(msg, sizeof(msg),
"Warning: the %s host key for '%.200s' "
"differs from the key for the IP address '%.128s'"
"\nOffending key for IP in %s:%lu",
type, host, ip, ip_found->file, ip_found->line);
if (host_status == HOST_OK) {
len = strlen(msg);
snprintf(msg + len, sizeof(msg) - len,
"\nMatching host key in %s:%lu",
host_found->file, host_found->line);
}
if (options.strict_host_key_checking == 1) {
logit("%s", msg);
error("Exiting, you have requested strict checking.");
goto fail;
} else if (options.strict_host_key_checking == 2) {
strlcat(msg, "\nAre you sure you want "
"to continue connecting (yes/no)? ", sizeof(msg));
if (!confirm(msg))
goto fail;
} else {
logit("%s", msg);
}
}
if (!hostkey_trusted && options.update_hostkeys) {
debug("%s: hostkey not known or explicitly trusted: "
"disabling UpdateHostkeys", __func__);
options.update_hostkeys = 0;
}
free(ip);
free(host);
if (host_hostkeys != NULL)
free_hostkeys(host_hostkeys);
if (ip_hostkeys != NULL)
free_hostkeys(ip_hostkeys);
return 0;
fail:
if (want_cert && host_status != HOST_REVOKED) {
/*
* No matching certificate. Downgrade cert to raw key and
* search normally.
*/
debug("No matching CA found. Retry with plain key");
raw_key = key_from_private(host_key);
if (key_drop_cert(raw_key) != 0)
fatal("Couldn't drop certificate");
host_key = raw_key;
goto retry;
}
if (raw_key != NULL)
key_free(raw_key);
free(ip);
free(host);
if (host_hostkeys != NULL)
free_hostkeys(host_hostkeys);
if (ip_hostkeys != NULL)
free_hostkeys(ip_hostkeys);
return -1;
}
/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
{
int r = -1, flags = 0;
char *fp = NULL;
struct sshkey *plain = NULL;
if ((fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error("%s: fingerprint host key: %s", __func__, ssh_err(r));
r = -1;
goto out;
}
debug("Server host key: %s %s",
compat20 ? sshkey_ssh_name(host_key) : sshkey_type(host_key), fp);
if (sshkey_equal(previous_host_key, host_key)) {
debug2("%s: server host key %s %s matches cached key",
__func__, sshkey_type(host_key), fp);
r = 0;
goto out;
}
/* Check in RevokedHostKeys file if specified */
if (options.revoked_host_keys != NULL) {
r = sshkey_check_revoked(host_key, options.revoked_host_keys);
switch (r) {
case 0:
break; /* not revoked */
case SSH_ERR_KEY_REVOKED:
error("Host key %s %s revoked by file %s",
sshkey_type(host_key), fp,
options.revoked_host_keys);
r = -1;
goto out;
default:
error("Error checking host key %s %s in "
"revoked keys file %s: %s", sshkey_type(host_key),
fp, options.revoked_host_keys, ssh_err(r));
r = -1;
goto out;
}
}
if (options.verify_host_key_dns) {
/*
* XXX certs are not yet supported for DNS, so downgrade
* them and try the plain key.
*/
if ((r = sshkey_from_private(host_key, &plain)) != 0)
goto out;
if (sshkey_is_cert(plain))
sshkey_drop_cert(plain);
if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
if (flags & DNS_VERIFY_FOUND) {
if (options.verify_host_key_dns == 1 &&
flags & DNS_VERIFY_MATCH &&
flags & DNS_VERIFY_SECURE) {
r = 0;
goto out;
}
if (flags & DNS_VERIFY_MATCH) {
matching_host_key_dns = 1;
} else {
warn_changed_key(plain);
error("Update the SSHFP RR in DNS "
"with the new host key to get rid "
"of this message.");
}
}
}
}
r = check_host_key(host, hostaddr, options.port, host_key, RDRW,
options.user_hostfiles, options.num_user_hostfiles,
options.system_hostfiles, options.num_system_hostfiles);
out:
sshkey_free(plain);
free(fp);
if (r == 0 && host_key != NULL) {
key_free(previous_host_key);
previous_host_key = key_from_private(host_key);
}
return r;
}
/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, struct sshkey *host_key)
{
u_int i;
int r = -1, flags = 0;
char valid[64], *fp = NULL, *cafp = NULL;
struct sshkey *plain = NULL;
if ((fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error("%s: fingerprint host key: %s", __func__, ssh_err(r));
r = -1;
goto out;
}
if (sshkey_is_cert(host_key)) {
if ((cafp = sshkey_fingerprint(host_key->cert->signature_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error("%s: fingerprint CA key: %s",
__func__, ssh_err(r));
r = -1;
goto out;
}
sshkey_format_cert_validity(host_key->cert,
valid, sizeof(valid));
debug("Server host certificate: %s %s, serial %llu "
"ID \"%s\" CA %s %s valid %s",
sshkey_ssh_name(host_key), fp,
(unsigned long long)host_key->cert->serial,
host_key->cert->key_id,
sshkey_ssh_name(host_key->cert->signature_key), cafp,
valid);
for (i = 0; i < host_key->cert->nprincipals; i++) {
debug2("Server host certificate hostname: %s",
host_key->cert->principals[i]);
}
} else {
debug("Server host key: %s %s", sshkey_ssh_name(host_key), fp);
}
if (sshkey_equal(previous_host_key, host_key)) {
debug2("%s: server host key %s %s matches cached key",
__func__, sshkey_type(host_key), fp);
r = 0;
goto out;
}
/* Check in RevokedHostKeys file if specified */
if (options.revoked_host_keys != NULL) {
r = sshkey_check_revoked(host_key, options.revoked_host_keys);
switch (r) {
case 0:
break; /* not revoked */
case SSH_ERR_KEY_REVOKED:
error("Host key %s %s revoked by file %s",
sshkey_type(host_key), fp,
options.revoked_host_keys);
r = -1;
goto out;
default:
error("Error checking host key %s %s in "
"revoked keys file %s: %s", sshkey_type(host_key),
fp, options.revoked_host_keys, ssh_err(r));
r = -1;
goto out;
}
}
if (options.verify_host_key_dns) {
/*
* XXX certs are not yet supported for DNS, so downgrade
* them and try the plain key.
*/
if ((r = sshkey_from_private(host_key, &plain)) != 0)
goto out;
if (sshkey_is_cert(plain))
sshkey_drop_cert(plain);
if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
if (flags & DNS_VERIFY_FOUND) {
if (options.verify_host_key_dns == 1 &&
flags & DNS_VERIFY_MATCH &&
flags & DNS_VERIFY_SECURE) {
r = 0;
goto out;
}
if (flags & DNS_VERIFY_MATCH) {
matching_host_key_dns = 1;
} else {
warn_changed_key(plain);
error("Update the SSHFP RR in DNS "
"with the new host key to get rid "
"of this message.");
}
}
}
}
r = check_host_key(host, hostaddr, options.port, host_key, RDRW,
options.user_hostfiles, options.num_user_hostfiles,
options.system_hostfiles, options.num_system_hostfiles);
out:
sshkey_free(plain);
free(fp);
free(cafp);
if (r == 0 && host_key != NULL) {
sshkey_free(previous_host_key);
r = sshkey_from_private(host_key, &previous_host_key);
}
return r;
}