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upstream: Add a sshd_config PubkeyAuthOptions directive 

This directive has a single valid option "no-touch-required" that
causes sshd to skip checking whether user presence was tested before
a security key signature was made (usually by the user touching the
key).

ok markus@

OpenBSD-Commit-ID: 46e434a49802d4ed82bc0aa38cb985c198c407de
This commit is contained in:
djm@openbsd.org 2019-11-25 00:52:46 +00:00 committed by Damien Miller
parent b7e74ea072
commit 0fddf2967a
5 changed files with 119 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
auth2-pubkey.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: auth2-pubkey.c,v 1.95 2019/11/25 00:51:37 djm Exp $ */
/* $OpenBSD: auth2-pubkey.c,v 1.96 2019/11/25 00:52:46 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
@ -68,6 +68,7 @@
#include "ssherr.h"
#include "channels.h" /* XXX for session.h */
#include "session.h" /* XXX for child_set_env(); refactor? */
#include "sk-api.h"
/* import */
extern ServerOptions options;
@ -96,7 +97,7 @@ userauth_pubkey(struct ssh *ssh)
u_char *pkblob = NULL, *sig = NULL, have_sig;
size_t blen, slen;
int r, pktype;
int authenticated = 0;
int req_presence = 0, authenticated = 0;
struct sshauthopt *authopts = NULL;
struct sshkey_sig_details *sig_details = NULL;
@ -217,10 +218,25 @@ userauth_pubkey(struct ssh *ssh)
ssh->compat, &sig_details)) == 0) {
authenticated = 1;
}
if (sig_details != NULL) {
if (authenticated == 1 && sig_details != NULL) {
auth2_record_info(authctxt, "signature count = %u",
sig_details->sk_counter);
debug("%s: sk_counter = %u, sk_flags = 0x%02x",
__func__, sig_details->sk_counter,
sig_details->sk_flags);
req_presence = (options.pubkey_auth_options &
PUBKEYAUTH_TOUCH_REQUIRED);
if (req_presence && (sig_details->sk_flags &
SSH_SK_USER_PRESENCE_REQD) == 0) {
error("public key %s signature for %s%s from "
"%.128s port %d rejected: user presence "
"(key touch) requirement not met ", key_s,
authctxt->valid ? "" : "invalid user ",
authctxt->user, ssh_remote_ipaddr(ssh),
ssh_remote_port(ssh));
authenticated = 0;
goto done;
}
}
auth2_record_key(authctxt, authenticated, key);
} else {

63
monitor.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: monitor.c,v 1.202 2019/11/25 00:51:37 djm Exp $ */
/* $OpenBSD: monitor.c,v 1.203 2019/11/25 00:52:46 djm Exp $ */
/*
* Copyright 2002 Niels Provos <provos@citi.umich.edu>
* Copyright 2002 Markus Friedl <markus@openbsd.org>
@ -95,6 +95,7 @@
#include "authfd.h"
#include "match.h"
#include "ssherr.h"
#include "sk-api.h"
#ifdef GSSAPI
static Gssctxt *gsscontext = NULL;
@ -542,7 +543,7 @@ monitor_read(struct ssh *ssh, struct monitor *pmonitor, struct mon_table *ent,
/* allowed key state */
static int
monitor_allowed_key(u_char *blob, u_int bloblen)
monitor_allowed_key(const u_char *blob, u_int bloblen)
{
/* make sure key is allowed */
if (key_blob == NULL || key_bloblen != bloblen ||
@ -1247,7 +1248,7 @@ mm_answer_keyallowed(struct ssh *ssh, int sock, struct sshbuf *m)
}
static int
monitor_valid_userblob(u_char *data, u_int datalen)
monitor_valid_userblob(const u_char *data, u_int datalen)
{
struct sshbuf *b;
const u_char *p;
@ -1256,10 +1257,8 @@ monitor_valid_userblob(u_char *data, u_int datalen)
u_char type;
int r, fail = 0;
if ((b = sshbuf_new()) == NULL)
fatal("%s: sshbuf_new", __func__);
if ((r = sshbuf_put(b, data, datalen)) != 0)
fatal("%s: buffer error: %s", __func__, ssh_err(r));
if ((b = sshbuf_from(data, datalen)) == NULL)
fatal("%s: sshbuf_from", __func__);
if (datafellows & SSH_OLD_SESSIONID) {
p = sshbuf_ptr(b);
@ -1314,8 +1313,8 @@ monitor_valid_userblob(u_char *data, u_int datalen)
}
static int
monitor_valid_hostbasedblob(u_char *data, u_int datalen, char *cuser,
char *chost)
monitor_valid_hostbasedblob(const u_char *data, u_int datalen,
const char *cuser, const char *chost)
{
struct sshbuf *b;
const u_char *p;
@ -1324,10 +1323,9 @@ monitor_valid_hostbasedblob(u_char *data, u_int datalen, char *cuser,
int r, fail = 0;
u_char type;
if ((b = sshbuf_new()) == NULL)
if ((b = sshbuf_from(data, datalen)) == NULL)
fatal("%s: sshbuf_new", __func__);
if ((r = sshbuf_put(b, data, datalen)) != 0 ||
(r = sshbuf_get_string_direct(b, &p, &len)) != 0)
if ((r = sshbuf_get_string_direct(b, &p, &len)) != 0)
fatal("%s: buffer error: %s", __func__, ssh_err(r));
if ((session_id2 == NULL) ||
@ -1387,15 +1385,15 @@ int
mm_answer_keyverify(struct ssh *ssh, int sock, struct sshbuf *m)
{
struct sshkey *key;
u_char *signature, *data, *blob;
char *sigalg;
const u_char *signature, *data, *blob;
char *sigalg = NULL, *fp = NULL;
size_t signaturelen, datalen, bloblen;
int r, ret, valid_data = 0, encoded_ret;
int r, ret, req_presence = 0, valid_data = 0, encoded_ret;
struct sshkey_sig_details *sig_details = NULL;
if ((r = sshbuf_get_string(m, &blob, &bloblen)) != 0 ||
(r = sshbuf_get_string(m, &signature, &signaturelen)) != 0 ||
(r = sshbuf_get_string(m, &data, &datalen)) != 0 ||
if ((r = sshbuf_get_string_direct(m, &blob, &bloblen)) != 0 ||
(r = sshbuf_get_string_direct(m, &signature, &signaturelen)) != 0 ||
(r = sshbuf_get_string_direct(m, &data, &datalen)) != 0 ||
(r = sshbuf_get_cstring(m, &sigalg, NULL)) != 0)
fatal("%s: buffer error: %s", __func__, ssh_err(r));
@ -1430,23 +1428,36 @@ mm_answer_keyverify(struct ssh *ssh, int sock, struct sshbuf *m)
if (!valid_data)
fatal("%s: bad signature data blob", __func__);
if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
SSH_FP_DEFAULT)) == NULL)
fatal("%s: sshkey_fingerprint failed", __func__);
ret = sshkey_verify(key, signature, signaturelen, data, datalen,
sigalg, ssh->compat, &sig_details);
debug3("%s: %s %p signature %s%s%s", __func__, auth_method, key,
(ret == 0) ? "verified" : "unverified",
(ret != 0) ? ": " : "", (ret != 0) ? ssh_err(ret) : "");
auth2_record_key(authctxt, ret == 0, key);
free(blob);
free(signature);
free(data);
free(sigalg);
if (ret == 0 && key_blobtype == MM_USERKEY && sig_details != NULL) {
req_presence = (options.pubkey_auth_options &
PUBKEYAUTH_TOUCH_REQUIRED);
if (req_presence &&
(sig_details->sk_flags & SSH_SK_USER_PRESENCE_REQD) == 0) {
error("public key %s %s signature for %s%s from %.128s "
"port %d rejected: user presence (key touch) "
"requirement not met ", sshkey_type(key), fp,
authctxt->valid ? "" : "invalid user ",
authctxt->user, ssh_remote_ipaddr(ssh),
ssh_remote_port(ssh));
ret = SSH_ERR_SIGNATURE_INVALID;
}
}
auth2_record_key(authctxt, ret == 0, key);
if (key_blobtype == MM_USERKEY)
auth_activate_options(ssh, key_opts);
monitor_reset_key_state();
sshkey_free(key);
sshbuf_reset(m);
/* encode ret != 0 as positive integer, since we're sending u32 */
@ -1462,6 +1473,10 @@ mm_answer_keyverify(struct ssh *ssh, int sock, struct sshbuf *m)
sshkey_sig_details_free(sig_details);
mm_request_send(sock, MONITOR_ANS_KEYVERIFY, m);
free(sigalg);
free(fp);
sshkey_free(key);
return ret == 0;
}

33
servconf.c
View File

@ -1,5 +1,5 @@
/* $OpenBSD: servconf.c,v 1.353 2019/10/31 21:17:49 djm Exp $ */
/* $OpenBSD: servconf.c,v 1.354 2019/11/25 00:52:46 djm Exp $ */
/*
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
@ -118,6 +118,7 @@ initialize_server_options(ServerOptions *options)
options->hostbased_key_types = NULL;
options->hostkeyalgorithms = NULL;
options->pubkey_authentication = -1;
options->pubkey_auth_options = -1;
options->pubkey_key_types = NULL;
options->kerberos_authentication = -1;
options->kerberos_or_local_passwd = -1;
@ -341,6 +342,8 @@ fill_default_server_options(ServerOptions *options)
options->hostbased_uses_name_from_packet_only = 0;
if (options->pubkey_authentication == -1)
options->pubkey_authentication = 1;
if (options->pubkey_auth_options == -1)
options->pubkey_auth_options = 0;
if (options->kerberos_authentication == -1)
options->kerberos_authentication = 0;
if (options->kerberos_or_local_passwd == -1)
@ -509,7 +512,7 @@ typedef enum {
sAuthenticationMethods, sHostKeyAgent, sPermitUserRC,
sStreamLocalBindMask, sStreamLocalBindUnlink,
sAllowStreamLocalForwarding, sFingerprintHash, sDisableForwarding,
sExposeAuthInfo, sRDomain,
sExposeAuthInfo, sRDomain, sPubkeyAuthOptions,
sDeprecated, sIgnore, sUnsupported
} ServerOpCodes;
@ -551,6 +554,7 @@ static struct {
{ "rsaauthentication", sDeprecated, SSHCFG_ALL },
{ "pubkeyauthentication", sPubkeyAuthentication, SSHCFG_ALL },
{ "pubkeyacceptedkeytypes", sPubkeyAcceptedKeyTypes, SSHCFG_ALL },
{ "pubkeyauthoptions", sPubkeyAuthOptions, SSHCFG_ALL },
{ "dsaauthentication", sPubkeyAuthentication, SSHCFG_GLOBAL }, /* alias */
#ifdef KRB5
{ "kerberosauthentication", sKerberosAuthentication, SSHCFG_ALL },
@ -1468,6 +1472,24 @@ process_server_config_line(ServerOptions *options, char *line,
charptr = &options->pubkey_key_types;
goto parse_keytypes;
case sPubkeyAuthOptions:
intptr = &options->pubkey_auth_options;
value = 0;
while ((arg = strdelim(&cp)) && *arg != '\0') {
if (strcasecmp(arg, "none") == 0)
continue;
if (strcasecmp(arg, "touch-required") == 0)
value |= PUBKEYAUTH_TOUCH_REQUIRED;
else {
fatal("%s line %d: unsupported "
"PubkeyAuthOptions option %s",
filename, linenum, arg);
}
}
if (*activep && *intptr == -1)
*intptr = value;
break;
case sKerberosAuthentication:
intptr = &options->kerberos_authentication;
goto parse_flag;
@ -2290,6 +2312,7 @@ copy_set_server_options(ServerOptions *dst, ServerOptions *src, int preauth)
M_CP_INTOPT(password_authentication);
M_CP_INTOPT(gss_authentication);
M_CP_INTOPT(pubkey_authentication);
M_CP_INTOPT(pubkey_auth_options);
M_CP_INTOPT(kerberos_authentication);
M_CP_INTOPT(hostbased_authentication);
M_CP_INTOPT(hostbased_uses_name_from_packet_only);
@ -2711,4 +2734,10 @@ dump_config(ServerOptions *o)
o->permit_user_env_whitelist);
}
printf("pubkeyauthoptions");
if (o->pubkey_auth_options == 0)
printf(" none");
if (o->pubkey_auth_options & PUBKEYAUTH_TOUCH_REQUIRED)
printf(" touch-required");
printf("\n");
}

6
servconf.h
View File

@ -1,4 +1,4 @@
/* $OpenBSD: servconf.h,v 1.140 2019/04/18 18:56:16 dtucker Exp $ */
/* $OpenBSD: servconf.h,v 1.141 2019/11/25 00:52:46 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -42,6 +42,9 @@
/* Magic name for internal sftp-server */
#define INTERNAL_SFTP_NAME "internal-sftp"
/* PubkeyAuthOptions flags */
#define PUBKEYAUTH_TOUCH_REQUIRED 1
struct ssh;
struct fwd_perm_list;
@ -114,6 +117,7 @@ typedef struct {
char *ca_sign_algorithms; /* Allowed CA signature algorithms */
int pubkey_authentication; /* If true, permit ssh2 pubkey authentication. */
char *pubkey_key_types; /* Key types allowed for public key */
int pubkey_auth_options; /* -1 or mask of PUBKEYAUTH_* flags */
int kerberos_authentication; /* If true, permit Kerberos
* authentication. */
int kerberos_or_local_passwd; /* If true, permit kerberos

27
sshd_config.5
View File

@ -33,8 +33,8 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $OpenBSD: sshd_config.5,v 1.292 2019/11/18 04:55:02 djm Exp $
.Dd $Mdocdate: November 18 2019 $
.\" $OpenBSD: sshd_config.5,v 1.293 2019/11/25 00:52:46 djm Exp $
.Dd $Mdocdate: November 25 2019 $
.Dt SSHD_CONFIG 5
.Os
.Sh NAME
@ -1444,6 +1444,29 @@ ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
.Pp
The list of available key types may also be obtained using
.Qq ssh -Q key .
.It Cm PubkeyAuthOptions
Sets one or more public key authentication options.
Two option keywords are currently supported:
.Cm none (the default; indicating no additional options are enabled)
and
.Cm touch-required .
.Pp
The
.Cm touch-required
option causes public key authentication using a security key algorithm
(i.e.
.Cm ecdsa-sk
or
.Cm ed25519-sk )
to always require the signature to attest that a physically present user
explicitly confirmed the authentication (usually by touching the security key).
By default,
.Xr sshd 8
requires key touch unless overridden with an authorized_keys option.
The
.Cm touch-required
flag disables this override.
This option has no effect for other, non-security key public key types.
.It Cm PubkeyAuthentication
Specifies whether public key authentication is allowed.
The default is