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/* $OpenBSD: ssh-sk-helper.c,v 1.3 2019/11/12 19:33:08 markus Exp $ */
/*
* Copyright (c) 2019 Google LLC
*
* 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.
*/
/*
* This is a tiny program used to isolate the address space used for
* security key middleware signing operations from ssh-agent. It is similar
* to ssh-pkcs11-helper.c but considerably simpler as the signing operation
* for this case are stateless.
*
* It receives a signing request (key, provider, message, flags) from
* stdin, attempts to perform a signature using the security key provider
* and returns the resultant signature via stdout.
*
* In the future, this program might gain additional functions to support
* FIDO2 tokens such as enumerating resident keys. When this happens it will
* be necessary to crank SSH_SK_HELPER_VERSION below.
*/
#include "includes.h"
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include "xmalloc.h"
#include "log.h"
#include "sshkey.h"
#include "authfd.h"
#include "misc.h"
#include "sshbuf.h"
#include "msg.h"
#include "uidswap.h"
#include "sshkey.h"
#include "ssherr.h"
#include "ssh-sk.h"
#ifdef ENABLE_SK
extern char *__progname;
int
main(int argc, char **argv)
{
SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
LogLevel log_level = SYSLOG_LEVEL_ERROR;
struct sshbuf *req, *resp, *kbuf;
struct sshkey *key;
uint32_t compat;
const u_char *message;
u_char version, *sig;
size_t msglen, siglen;
char *provider;
int in, out, ch, r, log_stderr = 0;
sanitise_stdfd();
log_init(__progname, log_level, log_facility, log_stderr);
while ((ch = getopt(argc, argv, "v")) != -1) {
switch (ch) {
case 'v':
log_stderr = 1;
if (log_level == SYSLOG_LEVEL_ERROR)
log_level = SYSLOG_LEVEL_DEBUG1;
else if (log_level < SYSLOG_LEVEL_DEBUG3)
log_level++;
break;
default:
fprintf(stderr, "usage: %s [-v]\n", __progname);
exit(1);
}
}
log_init(__progname, log_level, log_facility, log_stderr);
/*
* Rearrange our file descriptors a little; we don't trust the
* providers not to fiddle with stdin/out.
*/
closefrom(STDERR_FILENO + 1);
if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1)
fatal("%s: dup: %s", __progname, strerror(errno));
close(STDIN_FILENO);
close(STDOUT_FILENO);
sanitise_stdfd(); /* resets to /dev/null */
if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL)
fatal("%s: sshbuf_new failed", __progname);
if (ssh_msg_recv(in, req) < 0)
fatal("ssh_msg_recv failed");
close(in);
debug("%s: received message len %zu", __progname, sshbuf_len(req));
if ((r = sshbuf_get_u8(req, &version)) != 0)
fatal("%s: buffer error: %s", __progname, ssh_err(r));
if (version != SSH_SK_HELPER_VERSION) {
fatal("unsupported version: received %d, expected %d",
version, SSH_SK_HELPER_VERSION);
}
if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
(r = sshkey_private_deserialize(kbuf, &key)) != 0)
fatal("Unable to parse key: %s", ssh_err(r));
if (!sshkey_is_sk(key))
fatal("Unsupported key type %s", sshkey_ssh_name(key));
if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
(r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
(r = sshbuf_get_u32(req, &compat)) != 0)
fatal("%s: buffer error: %s", __progname, ssh_err(r));
if (sshbuf_len(req) != 0)
fatal("%s: trailing data in request", __progname);
debug("%s: ready to sign with key %s, provider %s: "
"msg len %zu, compat 0x%lx", __progname, sshkey_type(key),
provider, msglen, (u_long)compat);
if ((r = sshsk_sign(provider, key, &sig, &siglen,
message, msglen, compat)) != 0)
fatal("Signing failed: %s", ssh_err(r));
/* send reply */
if ((r = sshbuf_put_string(resp, sig, siglen)) != 0)
fatal("%s: buffer error: %s", __progname, ssh_err(r));
debug("%s: reply len %zu", __progname, sshbuf_len(resp));
if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1)
fatal("ssh_msg_send failed");
close(out);
return (0);
}
#else /* ENABLE_SK */
#include <stdio.h>
int
main(int argc, char **argv)
{
fprintf(stderr, "ssh-sk-helper: disabled at compile time\n");
return -1;
}
#endif /* ENABLE_SK */
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