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openssh/ssh-pkcs11-client.c

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/* $OpenBSD: ssh-pkcs11-client.c,v 1.19 2023/12/18 14:46:56 djm Exp $ */
/*
* Copyright (c) 2010 Markus Friedl. All rights reserved.
* Copyright (c) 2014 Pedro Martelletto. All rights reserved.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include "includes.h"
#ifdef ENABLE_PKCS11
#include <sys/types.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif
#include <sys/socket.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>
#include <openssl/ecdsa.h>
#include <openssl/rsa.h>
#include "pathnames.h"
#include "xmalloc.h"
#include "sshbuf.h"
#include "log.h"
#include "misc.h"
#include "sshkey.h"
#include "authfd.h"
#include "atomicio.h"
#include "ssh-pkcs11.h"
#include "ssherr.h"
#include "openbsd-compat/openssl-compat.h"
#if !defined(OPENSSL_HAS_ECC) || !defined(HAVE_EC_KEY_METHOD_NEW)
#define EC_KEY_METHOD void
#define EC_KEY void
#endif
/* borrows code from sftp-server and ssh-agent */
/*
* Maintain a list of ssh-pkcs11-helper subprocesses. These may be looked up
* by provider path or their unique EC/RSA METHOD pointers.
*/
struct helper {
char *path;
pid_t pid;
int fd;
RSA_METHOD *rsa_meth;
EC_KEY_METHOD *ec_meth;
int (*rsa_finish)(RSA *rsa);
void (*ec_finish)(EC_KEY *key);
size_t nrsa, nec; /* number of active keys of each type */
};
static struct helper **helpers;
static size_t nhelpers;
static struct helper *
helper_by_provider(const char *path)
{
size_t i;
for (i = 0; i < nhelpers; i++) {
if (helpers[i] == NULL || helpers[i]->path == NULL ||
helpers[i]->fd == -1)
continue;
if (strcmp(helpers[i]->path, path) == 0)
return helpers[i];
}
return NULL;
}
static struct helper *
helper_by_rsa(const RSA *rsa)
{
size_t i;
const RSA_METHOD *meth;
if ((meth = RSA_get_method(rsa)) == NULL)
return NULL;
for (i = 0; i < nhelpers; i++) {
if (helpers[i] != NULL && helpers[i]->rsa_meth == meth)
return helpers[i];
}
return NULL;
}
#if defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW)
static struct helper *
helper_by_ec(const EC_KEY *ec)
{
size_t i;
const EC_KEY_METHOD *meth;
if ((meth = EC_KEY_get_method(ec)) == NULL)
return NULL;
for (i = 0; i < nhelpers; i++) {
if (helpers[i] != NULL && helpers[i]->ec_meth == meth)
return helpers[i];
}
return NULL;
}
#endif /* defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW) */
static void
helper_free(struct helper *helper)
{
size_t i;
int found = 0;
if (helper == NULL)
return;
if (helper->path == NULL || helper->ec_meth == NULL ||
helper->rsa_meth == NULL)
fatal_f("inconsistent helper");
debug3_f("free helper for provider %s", helper->path);
for (i = 0; i < nhelpers; i++) {
if (helpers[i] == helper) {
if (found)
fatal_f("helper recorded more than once");
found = 1;
}
else if (found)
helpers[i - 1] = helpers[i];
}
if (found) {
helpers = xrecallocarray(helpers, nhelpers,
nhelpers - 1, sizeof(*helpers));
nhelpers--;
}
free(helper->path);
#if defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW)
EC_KEY_METHOD_free(helper->ec_meth);
#endif
RSA_meth_free(helper->rsa_meth);
free(helper);
}
static void
helper_terminate(struct helper *helper)
{
if (helper == NULL) {
return;
} else if (helper->fd == -1) {
debug3_f("already terminated");
} else {
debug3_f("terminating helper for %s; "
"remaining %zu RSA %zu ECDSA",
helper->path, helper->nrsa, helper->nec);
close(helper->fd);
/* XXX waitpid() */
helper->fd = -1;
helper->pid = -1;
}
/*
* Don't delete the helper entry until there are no remaining keys
* that reference it. Otherwise, any signing operation would call
* a free'd METHOD pointer and that would be bad.
*/
if (helper->nrsa == 0 && helper->nec == 0)
helper_free(helper);
}
static void
send_msg(int fd, struct sshbuf *m)
{
u_char buf[4];
size_t mlen = sshbuf_len(m);
int r;
if (fd == -1)
return;
POKE_U32(buf, mlen);
if (atomicio(vwrite, fd, buf, 4) != 4 ||
atomicio(vwrite, fd, sshbuf_mutable_ptr(m),
sshbuf_len(m)) != sshbuf_len(m))
error("write to helper failed");
if ((r = sshbuf_consume(m, mlen)) != 0)
fatal_fr(r, "consume");
}
static int
recv_msg(int fd, struct sshbuf *m)
{
u_int l, len;
u_char c, buf[1024];
int r;
sshbuf_reset(m);
if (fd == -1)
return 0; /* XXX */
if ((len = atomicio(read, fd, buf, 4)) != 4) {
error("read from helper failed: %u", len);
return (0); /* XXX */
}
len = PEEK_U32(buf);
if (len > 256 * 1024)
fatal("response too long: %u", len);
/* read len bytes into m */
while (len > 0) {
l = len;
if (l > sizeof(buf))
l = sizeof(buf);
if (atomicio(read, fd, buf, l) != l) {
error("response from helper failed.");
return (0); /* XXX */
}
if ((r = sshbuf_put(m, buf, l)) != 0)
fatal_fr(r, "sshbuf_put");
len -= l;
}
if ((r = sshbuf_get_u8(m, &c)) != 0)
fatal_fr(r, "parse type");
return c;
}
int
pkcs11_init(int interactive)
{
return 0;
}
void
pkcs11_terminate(void)
{
size_t i;
debug3_f("terminating %zu helpers", nhelpers);
for (i = 0; i < nhelpers; i++)
helper_terminate(helpers[i]);
}
static int
rsa_encrypt(int flen, const u_char *from, u_char *to, RSA *rsa, int padding)
{
struct sshkey *key = NULL;
struct sshbuf *msg = NULL;
u_char *blob = NULL, *signature = NULL;
size_t blen, slen = 0;
int r, ret = -1;
struct helper *helper;
if ((helper = helper_by_rsa(rsa)) == NULL || helper->fd == -1)
fatal_f("no helper for PKCS11 key");
debug3_f("signing with PKCS11 provider %s", helper->path);
if (padding != RSA_PKCS1_PADDING)
goto fail;
key = sshkey_new(KEY_UNSPEC);
if (key == NULL) {
error_f("sshkey_new failed");
goto fail;
}
key->type = KEY_RSA;
RSA_up_ref(rsa);
key->rsa = rsa;
if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
error_fr(r, "encode key");
goto fail;
}
if ((msg = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 ||
(r = sshbuf_put_string(msg, blob, blen)) != 0 ||
(r = sshbuf_put_string(msg, from, flen)) != 0 ||
(r = sshbuf_put_u32(msg, 0)) != 0)
fatal_fr(r, "compose");
send_msg(helper->fd, msg);
sshbuf_reset(msg);
if (recv_msg(helper->fd, msg) == SSH2_AGENT_SIGN_RESPONSE) {
if ((r = sshbuf_get_string(msg, &signature, &slen)) != 0)
fatal_fr(r, "parse");
if (slen <= (size_t)RSA_size(rsa)) {
memcpy(to, signature, slen);
ret = slen;
}
free(signature);
}
fail:
free(blob);
sshkey_free(key);
sshbuf_free(msg);
return (ret);
}
static int
rsa_finish(RSA *rsa)
{
struct helper *helper;
if ((helper = helper_by_rsa(rsa)) == NULL)
fatal_f("no helper for PKCS11 key");
debug3_f("free PKCS11 RSA key for provider %s", helper->path);
if (helper->rsa_finish != NULL)
helper->rsa_finish(rsa);
if (helper->nrsa == 0)
fatal_f("RSA refcount error");
helper->nrsa--;
debug3_f("provider %s remaining keys: %zu RSA %zu ECDSA",
helper->path, helper->nrsa, helper->nec);
if (helper->nrsa == 0 && helper->nec == 0)
helper_terminate(helper);
return 1;
}
#if defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW)
static ECDSA_SIG *
ecdsa_do_sign(const unsigned char *dgst, int dgst_len, const BIGNUM *inv,
const BIGNUM *rp, EC_KEY *ec)
{
struct sshkey *key = NULL;
struct sshbuf *msg = NULL;
ECDSA_SIG *ret = NULL;
const u_char *cp;
u_char *blob = NULL, *signature = NULL;
size_t blen, slen = 0;
int r, nid;
struct helper *helper;
if ((helper = helper_by_ec(ec)) == NULL || helper->fd == -1)
fatal_f("no helper for PKCS11 key");
debug3_f("signing with PKCS11 provider %s", helper->path);
nid = sshkey_ecdsa_key_to_nid(ec);
if (nid < 0) {
error_f("couldn't get curve nid");
goto fail;
}
key = sshkey_new(KEY_UNSPEC);
if (key == NULL) {
error_f("sshkey_new failed");
goto fail;
}
key->ecdsa = ec;
key->ecdsa_nid = nid;
key->type = KEY_ECDSA;
EC_KEY_up_ref(ec);
if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
error_fr(r, "encode key");
goto fail;
}
if ((msg = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 ||
(r = sshbuf_put_string(msg, blob, blen)) != 0 ||
(r = sshbuf_put_string(msg, dgst, dgst_len)) != 0 ||
(r = sshbuf_put_u32(msg, 0)) != 0)
fatal_fr(r, "compose");
send_msg(helper->fd, msg);
sshbuf_reset(msg);
if (recv_msg(helper->fd, msg) == SSH2_AGENT_SIGN_RESPONSE) {
if ((r = sshbuf_get_string(msg, &signature, &slen)) != 0)
fatal_fr(r, "parse");
cp = signature;
ret = d2i_ECDSA_SIG(NULL, &cp, slen);
free(signature);
}
fail:
free(blob);
sshkey_free(key);
sshbuf_free(msg);
return (ret);
}
static void
ecdsa_do_finish(EC_KEY *ec)
{
struct helper *helper;
if ((helper = helper_by_ec(ec)) == NULL)
fatal_f("no helper for PKCS11 key");
debug3_f("free PKCS11 ECDSA key for provider %s", helper->path);
if (helper->ec_finish != NULL)
helper->ec_finish(ec);
if (helper->nec == 0)
fatal_f("ECDSA refcount error");
helper->nec--;
debug3_f("provider %s remaining keys: %zu RSA %zu ECDSA",
helper->path, helper->nrsa, helper->nec);
if (helper->nrsa == 0 && helper->nec == 0)
helper_terminate(helper);
}
#endif /* defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW) */
/* redirect private key crypto operations to the ssh-pkcs11-helper */
static void
wrap_key(struct helper *helper, struct sshkey *k)
{
debug3_f("wrap %s for provider %s", sshkey_type(k), helper->path);
if (k->type == KEY_RSA) {
RSA_set_method(k->rsa, helper->rsa_meth);
if (helper->nrsa++ >= INT_MAX)
fatal_f("RSA refcount error");
#if defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW)
} else if (k->type == KEY_ECDSA) {
EC_KEY_set_method(k->ecdsa, helper->ec_meth);
if (helper->nec++ >= INT_MAX)
fatal_f("EC refcount error");
#endif
} else
fatal_f("unknown key type");
k->flags |= SSHKEY_FLAG_EXT;
debug3_f("provider %s remaining keys: %zu RSA %zu ECDSA",
helper->path, helper->nrsa, helper->nec);
}
/*
* Make a private PKCS#11-backed certificate by grafting a previously-loaded
* PKCS#11 private key and a public certificate key.
*/
int
pkcs11_make_cert(const struct sshkey *priv,
const struct sshkey *certpub, struct sshkey **certprivp)
{
struct helper *helper = NULL;
struct sshkey *ret;
int r;
debug3_f("private key type %s cert type %s", sshkey_type(priv),
sshkey_type(certpub));
*certprivp = NULL;
if (!sshkey_is_cert(certpub) || sshkey_is_cert(priv) ||
!sshkey_equal_public(priv, certpub)) {
error_f("private key %s doesn't match cert %s",
sshkey_type(priv), sshkey_type(certpub));
return SSH_ERR_INVALID_ARGUMENT;
}
*certprivp = NULL;
if (priv->type == KEY_RSA) {
if ((helper = helper_by_rsa(priv->rsa)) == NULL ||
helper->fd == -1)
fatal_f("no helper for PKCS11 RSA key");
if ((r = sshkey_from_private(priv, &ret)) != 0)
fatal_fr(r, "copy key");
RSA_set_method(ret->rsa, helper->rsa_meth);
if (helper->nrsa++ >= INT_MAX)
fatal_f("RSA refcount error");
} else if (priv->type == KEY_ECDSA) {
if ((helper = helper_by_ec(priv->ecdsa)) == NULL ||
helper->fd == -1)
fatal_f("no helper for PKCS11 EC key");
if ((r = sshkey_from_private(priv, &ret)) != 0)
fatal_fr(r, "copy key");
EC_KEY_set_method(ret->ecdsa, helper->ec_meth);
if (helper->nec++ >= INT_MAX)
fatal_f("EC refcount error");
} else
fatal_f("unknown key type %s", sshkey_type(priv));
ret->flags |= SSHKEY_FLAG_EXT;
if ((r = sshkey_to_certified(ret)) != 0 ||
(r = sshkey_cert_copy(certpub, ret)) != 0)
fatal_fr(r, "graft certificate");
debug3_f("provider %s remaining keys: %zu RSA %zu ECDSA",
helper->path, helper->nrsa, helper->nec);
/* success */
*certprivp = ret;
return 0;
}
static int
pkcs11_start_helper_methods(struct helper *helper)
{
RSA_METHOD *rsa_meth;
EC_KEY_METHOD *ec_meth = NULL;
#if defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW)
int (*ec_init)(EC_KEY *key);
int (*ec_copy)(EC_KEY *dest, const EC_KEY *src);
int (*ec_set_group)(EC_KEY *key, const EC_GROUP *grp);
int (*ec_set_private)(EC_KEY *key, const BIGNUM *priv_key);
int (*ec_set_public)(EC_KEY *key, const EC_POINT *pub_key);
int (*ec_sign)(int, const unsigned char *, int, unsigned char *,
unsigned int *, const BIGNUM *, const BIGNUM *, EC_KEY *) = NULL;
if ((ec_meth = EC_KEY_METHOD_new(EC_KEY_OpenSSL())) == NULL)
return -1;
EC_KEY_METHOD_get_sign(ec_meth, &ec_sign, NULL, NULL);
EC_KEY_METHOD_set_sign(ec_meth, ec_sign, NULL, ecdsa_do_sign);
EC_KEY_METHOD_get_init(ec_meth, &ec_init, &helper->ec_finish,
&ec_copy, &ec_set_group, &ec_set_private, &ec_set_public);
EC_KEY_METHOD_set_init(ec_meth, ec_init, ecdsa_do_finish,
ec_copy, ec_set_group, ec_set_private, ec_set_public);
#endif /* defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW) */
if ((rsa_meth = RSA_meth_dup(RSA_get_default_method())) == NULL)
fatal_f("RSA_meth_dup failed");
helper->rsa_finish = RSA_meth_get_finish(rsa_meth);
if (!RSA_meth_set1_name(rsa_meth, "ssh-pkcs11-helper") ||
!RSA_meth_set_priv_enc(rsa_meth, rsa_encrypt) ||
!RSA_meth_set_finish(rsa_meth, rsa_finish))
fatal_f("failed to prepare method");
helper->ec_meth = ec_meth;
helper->rsa_meth = rsa_meth;
return 0;
}
static struct helper *
pkcs11_start_helper(const char *path)
{
int pair[2];
char *prog, *verbosity = NULL;
struct helper *helper;
pid_t pid;
if (nhelpers >= INT_MAX)
fatal_f("too many helpers");
debug3_f("start helper for %s", path);
if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
error_f("socketpair: %s", strerror(errno));
return NULL;
}
helper = xcalloc(1, sizeof(*helper));
if (pkcs11_start_helper_methods(helper) == -1) {
error_f("pkcs11_start_helper_methods failed");
goto fail;
}
if ((pid = fork()) == -1) {
error_f("fork: %s", strerror(errno));
fail:
close(pair[0]);
close(pair[1]);
RSA_meth_free(helper->rsa_meth);
#if defined(OPENSSL_HAS_ECC) && defined(HAVE_EC_KEY_METHOD_NEW)
EC_KEY_METHOD_free(helper->ec_meth);
#endif
free(helper);
return NULL;
} else if (pid == 0) {
if ((dup2(pair[1], STDIN_FILENO) == -1) ||
(dup2(pair[1], STDOUT_FILENO) == -1)) {
fprintf(stderr, "dup2: %s\n", strerror(errno));
_exit(1);
}
close(pair[0]);
close(pair[1]);
prog = getenv("SSH_PKCS11_HELPER");
if (prog == NULL || strlen(prog) == 0)
prog = _PATH_SSH_PKCS11_HELPER;
if (log_level_get() >= SYSLOG_LEVEL_DEBUG1)
verbosity = "-vvv";
debug_f("starting %s %s", prog,
verbosity == NULL ? "" : verbosity);
execlp(prog, prog, verbosity, (char *)NULL);
fprintf(stderr, "exec: %s: %s\n", prog, strerror(errno));
_exit(1);
}
close(pair[1]);
helper->fd = pair[0];
helper->path = xstrdup(path);
helper->pid = pid;
debug3_f("helper %zu for \"%s\" on fd %d pid %ld", nhelpers,
helper->path, helper->fd, (long)helper->pid);
helpers = xrecallocarray(helpers, nhelpers,
nhelpers + 1, sizeof(*helpers));
helpers[nhelpers++] = helper;
return helper;
}
int
pkcs11_add_provider(char *name, char *pin, struct sshkey ***keysp,
char ***labelsp)
{
struct sshkey *k;
int r, type;
u_char *blob;
char *label;
size_t blen;
u_int nkeys, i;
struct sshbuf *msg;
struct helper *helper;
if ((helper = helper_by_provider(name)) == NULL &&
(helper = pkcs11_start_helper(name)) == NULL)
return -1;
if ((msg = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
if ((r = sshbuf_put_u8(msg, SSH_AGENTC_ADD_SMARTCARD_KEY)) != 0 ||
(r = sshbuf_put_cstring(msg, name)) != 0 ||
(r = sshbuf_put_cstring(msg, pin)) != 0)
fatal_fr(r, "compose");
send_msg(helper->fd, msg);
sshbuf_reset(msg);
type = recv_msg(helper->fd, msg);
if (type == SSH2_AGENT_IDENTITIES_ANSWER) {
if ((r = sshbuf_get_u32(msg, &nkeys)) != 0)
fatal_fr(r, "parse nkeys");
*keysp = xcalloc(nkeys, sizeof(struct sshkey *));
if (labelsp)
*labelsp = xcalloc(nkeys, sizeof(char *));
for (i = 0; i < nkeys; i++) {
/* XXX clean up properly instead of fatal() */
if ((r = sshbuf_get_string(msg, &blob, &blen)) != 0 ||
(r = sshbuf_get_cstring(msg, &label, NULL)) != 0)
fatal_fr(r, "parse key");
if ((r = sshkey_from_blob(blob, blen, &k)) != 0)
fatal_fr(r, "decode key");
wrap_key(helper, k);
(*keysp)[i] = k;
if (labelsp)
(*labelsp)[i] = label;
else
free(label);
free(blob);
}
} else if (type == SSH2_AGENT_FAILURE) {
if ((r = sshbuf_get_u32(msg, &nkeys)) != 0)
nkeys = -1;
} else {
nkeys = -1;
}
sshbuf_free(msg);
return (nkeys);
}
int
pkcs11_del_provider(char *name)
{
struct helper *helper;
/*
* ssh-agent deletes keys before calling this, so the helper entry
* should be gone before we get here.
*/
debug3_f("delete %s", name);
if ((helper = helper_by_provider(name)) != NULL)
helper_terminate(helper);
return 0;
}
#endif /* ENABLE_PKCS11 */
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