This release fixes a number of security bugs and has minor new features and bug fixes. Security fixes, from the release notes (https://www.openssh.com/txt/release-9.3): This release contains fixes for a security problem and a memory safety problem. The memory safety problem is not believed to be exploitable, but we report most network-reachable memory faults as security bugs. * ssh-add(1): when adding smartcard keys to ssh-agent(1) with the per-hop destination constraints (ssh-add -h ...) added in OpenSSH 8.9, a logic error prevented the constraints from being communicated to the agent. This resulted in the keys being added without constraints. The common cases of non-smartcard keys and keys without destination constraints are unaffected. This problem was reported by Luci Stanescu. * ssh(1): Portable OpenSSH provides an implementation of the getrrsetbyname(3) function if the standard library does not provide it, for use by the VerifyHostKeyDNS feature. A specifically crafted DNS response could cause this function to perform an out-of-bounds read of adjacent stack data, but this condition does not appear to be exploitable beyond denial-of- service to the ssh(1) client. The getrrsetbyname(3) replacement is only included if the system's standard library lacks this function and portable OpenSSH was not compiled with the ldns library (--with-ldns). getrrsetbyname(3) is only invoked if using VerifyHostKeyDNS to fetch SSHFP records. This problem was found by the Coverity static analyzer. Sponsored by: The FreeBSD Foundation
468 lines
14 KiB
C
468 lines
14 KiB
C
/* $OpenBSD: ssh-ecdsa-sk.c,v 1.18 2023/03/08 04:43:12 guenther Exp $ */
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/*
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* Copyright (c) 2000 Markus Friedl. All rights reserved.
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* Copyright (c) 2010 Damien Miller. All rights reserved.
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* Copyright (c) 2019 Google Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/* #define DEBUG_SK 1 */
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#include "includes.h"
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#include <sys/types.h>
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#ifdef WITH_OPENSSL
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#include <openssl/bn.h>
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#include <openssl/ec.h>
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#include <openssl/ecdsa.h>
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#include <openssl/evp.h>
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#endif
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#include <string.h>
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#include <stdio.h> /* needed for DEBUG_SK only */
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#include "openbsd-compat/openssl-compat.h"
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#include "sshbuf.h"
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#include "ssherr.h"
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#include "digest.h"
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#define SSHKEY_INTERNAL
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#include "sshkey.h"
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#ifndef OPENSSL_HAS_ECC
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/* ARGSUSED */
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int
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ssh_ecdsa_sk_verify(const struct sshkey *key,
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const u_char *signature, size_t signaturelen,
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const u_char *data, size_t datalen, u_int compat,
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struct sshkey_sig_details **detailsp)
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{
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return SSH_ERR_FEATURE_UNSUPPORTED;
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}
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#else /* OPENSSL_HAS_ECC */
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/* Reuse some ECDSA internals */
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extern struct sshkey_impl_funcs sshkey_ecdsa_funcs;
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static void
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ssh_ecdsa_sk_cleanup(struct sshkey *k)
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{
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sshkey_sk_cleanup(k);
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sshkey_ecdsa_funcs.cleanup(k);
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}
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static int
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ssh_ecdsa_sk_equal(const struct sshkey *a, const struct sshkey *b)
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{
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if (!sshkey_sk_fields_equal(a, b))
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return 0;
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if (!sshkey_ecdsa_funcs.equal(a, b))
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return 0;
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return 1;
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}
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static int
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ssh_ecdsa_sk_serialize_public(const struct sshkey *key, struct sshbuf *b,
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enum sshkey_serialize_rep opts)
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{
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int r;
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if ((r = sshkey_ecdsa_funcs.serialize_public(key, b, opts)) != 0)
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return r;
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if ((r = sshkey_serialize_sk(key, b)) != 0)
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return r;
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return 0;
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}
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static int
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ssh_ecdsa_sk_serialize_private(const struct sshkey *key, struct sshbuf *b,
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enum sshkey_serialize_rep opts)
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{
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int r;
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if (!sshkey_is_cert(key)) {
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if ((r = sshkey_ecdsa_funcs.serialize_public(key,
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b, opts)) != 0)
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return r;
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}
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if ((r = sshkey_serialize_private_sk(key, b)) != 0)
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return r;
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return 0;
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}
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static int
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ssh_ecdsa_sk_copy_public(const struct sshkey *from, struct sshkey *to)
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{
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int r;
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if ((r = sshkey_ecdsa_funcs.copy_public(from, to)) != 0)
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return r;
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if ((r = sshkey_copy_public_sk(from, to)) != 0)
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return r;
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return 0;
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}
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static int
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ssh_ecdsa_sk_deserialize_public(const char *ktype, struct sshbuf *b,
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struct sshkey *key)
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{
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int r;
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if ((r = sshkey_ecdsa_funcs.deserialize_public(ktype, b, key)) != 0)
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return r;
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if ((r = sshkey_deserialize_sk(b, key)) != 0)
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return r;
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return 0;
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}
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static int
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ssh_ecdsa_sk_deserialize_private(const char *ktype, struct sshbuf *b,
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struct sshkey *key)
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{
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int r;
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if (!sshkey_is_cert(key)) {
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if ((r = sshkey_ecdsa_funcs.deserialize_public(ktype,
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b, key)) != 0)
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return r;
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}
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if ((r = sshkey_private_deserialize_sk(b, key)) != 0)
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return r;
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return 0;
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}
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/*
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* Check FIDO/W3C webauthn signatures clientData field against the expected
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* format and prepare a hash of it for use in signature verification.
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*
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* webauthn signatures do not sign the hash of the message directly, but
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* instead sign a JSON-like "clientData" wrapper structure that contains the
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* message hash along with a other information.
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*
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* Fortunately this structure has a fixed format so it is possible to verify
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* that the hash of the signed message is present within the clientData
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* structure without needing to implement any JSON parsing.
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*/
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static int
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webauthn_check_prepare_hash(const u_char *data, size_t datalen,
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const char *origin, const struct sshbuf *wrapper,
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uint8_t flags, const struct sshbuf *extensions,
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u_char *msghash, size_t msghashlen)
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{
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int r = SSH_ERR_INTERNAL_ERROR;
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struct sshbuf *chall = NULL, *m = NULL;
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if ((m = sshbuf_new()) == NULL ||
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(chall = sshbuf_from(data, datalen)) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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/*
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* Ensure origin contains no quote character and that the flags are
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* consistent with what we received
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*/
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if (strchr(origin, '\"') != NULL ||
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(flags & 0x40) != 0 /* AD */ ||
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((flags & 0x80) == 0 /* ED */) != (sshbuf_len(extensions) == 0)) {
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r = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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/*
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* Prepare the preamble to clientData that we expect, poking the
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* challenge and origin into their canonical positions in the
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* structure. The crossOrigin flag and any additional extension
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* fields present are ignored.
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*/
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#define WEBAUTHN_0 "{\"type\":\"webauthn.get\",\"challenge\":\""
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#define WEBAUTHN_1 "\",\"origin\":\""
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#define WEBAUTHN_2 "\""
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if ((r = sshbuf_put(m, WEBAUTHN_0, sizeof(WEBAUTHN_0) - 1)) != 0 ||
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(r = sshbuf_dtourlb64(chall, m, 0)) != 0 ||
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(r = sshbuf_put(m, WEBAUTHN_1, sizeof(WEBAUTHN_1) - 1)) != 0 ||
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(r = sshbuf_put(m, origin, strlen(origin))) != 0 ||
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(r = sshbuf_put(m, WEBAUTHN_2, sizeof(WEBAUTHN_2) - 1)) != 0)
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goto out;
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#ifdef DEBUG_SK
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fprintf(stderr, "%s: received origin: %s\n", __func__, origin);
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fprintf(stderr, "%s: received clientData:\n", __func__);
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sshbuf_dump(wrapper, stderr);
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fprintf(stderr, "%s: expected clientData premable:\n", __func__);
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sshbuf_dump(m, stderr);
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#endif
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/* Check that the supplied clientData has the preamble we expect */
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if ((r = sshbuf_cmp(wrapper, 0, sshbuf_ptr(m), sshbuf_len(m))) != 0)
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goto out;
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/* Prepare hash of clientData */
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if ((r = ssh_digest_buffer(SSH_DIGEST_SHA256, wrapper,
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msghash, msghashlen)) != 0)
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goto out;
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/* success */
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r = 0;
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out:
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sshbuf_free(chall);
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sshbuf_free(m);
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return r;
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}
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static int
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ssh_ecdsa_sk_verify(const struct sshkey *key,
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const u_char *sig, size_t siglen,
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const u_char *data, size_t dlen, const char *alg, u_int compat,
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struct sshkey_sig_details **detailsp)
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{
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ECDSA_SIG *esig = NULL;
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BIGNUM *sig_r = NULL, *sig_s = NULL;
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u_char sig_flags;
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u_char msghash[32], apphash[32], sighash[32];
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u_int sig_counter;
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int is_webauthn = 0, ret = SSH_ERR_INTERNAL_ERROR;
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struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL;
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struct sshbuf *webauthn_wrapper = NULL, *webauthn_exts = NULL;
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char *ktype = NULL, *webauthn_origin = NULL;
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struct sshkey_sig_details *details = NULL;
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#ifdef DEBUG_SK
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char *tmp = NULL;
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#endif
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if (detailsp != NULL)
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*detailsp = NULL;
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if (key == NULL || key->ecdsa == NULL ||
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sshkey_type_plain(key->type) != KEY_ECDSA_SK ||
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sig == NULL || siglen == 0)
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return SSH_ERR_INVALID_ARGUMENT;
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if (key->ecdsa_nid != NID_X9_62_prime256v1)
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return SSH_ERR_INTERNAL_ERROR;
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/* fetch signature */
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if ((b = sshbuf_from(sig, siglen)) == NULL)
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return SSH_ERR_ALLOC_FAIL;
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if ((details = calloc(1, sizeof(*details))) == NULL) {
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ret = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
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ret = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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if (strcmp(ktype, "webauthn-sk-ecdsa-sha2-nistp256@openssh.com") == 0)
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is_webauthn = 1;
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else if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) {
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ret = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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if (sshbuf_froms(b, &sigbuf) != 0 ||
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sshbuf_get_u8(b, &sig_flags) != 0 ||
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sshbuf_get_u32(b, &sig_counter) != 0) {
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ret = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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if (is_webauthn) {
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if (sshbuf_get_cstring(b, &webauthn_origin, NULL) != 0 ||
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sshbuf_froms(b, &webauthn_wrapper) != 0 ||
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sshbuf_froms(b, &webauthn_exts) != 0) {
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ret = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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}
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if (sshbuf_len(b) != 0) {
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ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
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goto out;
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}
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/* parse signature */
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if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 ||
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sshbuf_get_bignum2(sigbuf, &sig_s) != 0) {
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ret = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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if (sshbuf_len(sigbuf) != 0) {
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ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
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goto out;
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}
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#ifdef DEBUG_SK
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fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen);
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/* sshbuf_dump_data(data, datalen, stderr); */
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fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r)));
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free(tmp);
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fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s)));
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free(tmp);
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fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
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__func__, sig_flags, sig_counter);
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if (is_webauthn) {
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fprintf(stderr, "%s: webauthn origin: %s\n", __func__,
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webauthn_origin);
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fprintf(stderr, "%s: webauthn_wrapper:\n", __func__);
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sshbuf_dump(webauthn_wrapper, stderr);
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}
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#endif
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if ((esig = ECDSA_SIG_new()) == NULL) {
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ret = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if (!ECDSA_SIG_set0(esig, sig_r, sig_s)) {
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ret = SSH_ERR_LIBCRYPTO_ERROR;
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goto out;
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}
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sig_r = sig_s = NULL; /* transferred */
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/* Reconstruct data that was supposedly signed */
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if ((original_signed = sshbuf_new()) == NULL) {
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ret = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if (is_webauthn) {
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if ((ret = webauthn_check_prepare_hash(data, dlen,
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webauthn_origin, webauthn_wrapper, sig_flags, webauthn_exts,
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msghash, sizeof(msghash))) != 0)
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goto out;
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} else if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, dlen,
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msghash, sizeof(msghash))) != 0)
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goto out;
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/* Application value is hashed before signature */
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if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application,
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strlen(key->sk_application), apphash, sizeof(apphash))) != 0)
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goto out;
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#ifdef DEBUG_SK
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fprintf(stderr, "%s: hashed application:\n", __func__);
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sshbuf_dump_data(apphash, sizeof(apphash), stderr);
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fprintf(stderr, "%s: hashed message:\n", __func__);
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sshbuf_dump_data(msghash, sizeof(msghash), stderr);
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#endif
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if ((ret = sshbuf_put(original_signed,
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apphash, sizeof(apphash))) != 0 ||
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(ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 ||
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(ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 ||
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(ret = sshbuf_putb(original_signed, webauthn_exts)) != 0 ||
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(ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0)
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goto out;
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/* Signature is over H(original_signed) */
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if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed,
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sighash, sizeof(sighash))) != 0)
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goto out;
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details->sk_counter = sig_counter;
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details->sk_flags = sig_flags;
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#ifdef DEBUG_SK
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fprintf(stderr, "%s: signed buf:\n", __func__);
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sshbuf_dump(original_signed, stderr);
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fprintf(stderr, "%s: signed hash:\n", __func__);
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sshbuf_dump_data(sighash, sizeof(sighash), stderr);
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#endif
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/* Verify it */
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switch (ECDSA_do_verify(sighash, sizeof(sighash), esig, key->ecdsa)) {
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case 1:
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ret = 0;
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break;
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case 0:
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ret = SSH_ERR_SIGNATURE_INVALID;
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goto out;
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default:
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ret = SSH_ERR_LIBCRYPTO_ERROR;
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goto out;
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}
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/* success */
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if (detailsp != NULL) {
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*detailsp = details;
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details = NULL;
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}
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out:
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explicit_bzero(&sig_flags, sizeof(sig_flags));
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explicit_bzero(&sig_counter, sizeof(sig_counter));
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explicit_bzero(msghash, sizeof(msghash));
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explicit_bzero(sighash, sizeof(msghash));
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explicit_bzero(apphash, sizeof(apphash));
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sshkey_sig_details_free(details);
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sshbuf_free(webauthn_wrapper);
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sshbuf_free(webauthn_exts);
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free(webauthn_origin);
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sshbuf_free(original_signed);
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sshbuf_free(sigbuf);
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sshbuf_free(b);
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ECDSA_SIG_free(esig);
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BN_clear_free(sig_r);
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BN_clear_free(sig_s);
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free(ktype);
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return ret;
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}
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static const struct sshkey_impl_funcs sshkey_ecdsa_sk_funcs = {
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/* .size = */ NULL,
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/* .alloc = */ NULL,
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/* .cleanup = */ ssh_ecdsa_sk_cleanup,
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/* .equal = */ ssh_ecdsa_sk_equal,
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/* .ssh_serialize_public = */ ssh_ecdsa_sk_serialize_public,
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/* .ssh_deserialize_public = */ ssh_ecdsa_sk_deserialize_public,
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/* .ssh_serialize_private = */ ssh_ecdsa_sk_serialize_private,
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/* .ssh_deserialize_private = */ ssh_ecdsa_sk_deserialize_private,
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/* .generate = */ NULL,
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/* .copy_public = */ ssh_ecdsa_sk_copy_public,
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/* .sign = */ NULL,
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/* .verify = */ ssh_ecdsa_sk_verify,
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};
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|
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const struct sshkey_impl sshkey_ecdsa_sk_impl = {
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/* .name = */ "sk-ecdsa-sha2-nistp256@openssh.com",
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/* .shortname = */ "ECDSA-SK",
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/* .sigalg = */ NULL,
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/* .type = */ KEY_ECDSA_SK,
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/* .nid = */ NID_X9_62_prime256v1,
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/* .cert = */ 0,
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/* .sigonly = */ 0,
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/* .keybits = */ 256,
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/* .funcs = */ &sshkey_ecdsa_sk_funcs,
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};
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const struct sshkey_impl sshkey_ecdsa_sk_cert_impl = {
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/* .name = */ "sk-ecdsa-sha2-nistp256-cert-v01@openssh.com",
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/* .shortname = */ "ECDSA-SK-CERT",
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|
/* .sigalg = */ NULL,
|
|
/* .type = */ KEY_ECDSA_SK_CERT,
|
|
/* .nid = */ NID_X9_62_prime256v1,
|
|
/* .cert = */ 1,
|
|
/* .sigonly = */ 0,
|
|
/* .keybits = */ 256,
|
|
/* .funcs = */ &sshkey_ecdsa_sk_funcs,
|
|
};
|
|
|
|
const struct sshkey_impl sshkey_ecdsa_sk_webauthn_impl = {
|
|
/* .name = */ "webauthn-sk-ecdsa-sha2-nistp256@openssh.com",
|
|
/* .shortname = */ "ECDSA-SK",
|
|
/* .sigalg = */ NULL,
|
|
/* .type = */ KEY_ECDSA_SK,
|
|
/* .nid = */ NID_X9_62_prime256v1,
|
|
/* .cert = */ 0,
|
|
/* .sigonly = */ 1,
|
|
/* .keybits = */ 256,
|
|
/* .funcs = */ &sshkey_ecdsa_sk_funcs,
|
|
};
|
|
|
|
#endif /* OPENSSL_HAS_ECC */
|