155 lines
4.8 KiB
C
155 lines
4.8 KiB
C
/* $OpenBSD: ssh-sk-helper.c,v 1.1 2019/10/31 21:22:01 djm Exp $ */
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/*
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* Copyright (c) 2019 Google LLC
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/*
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* This is a tiny program used to isolate the address space used for
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* security key middleware signing operations from ssh-agent. It is similar
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* to ssh-pkcs11-helper.c but considerably simpler as the signing operation
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* for this case are stateless.
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*
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* It receives a signing request (key, provider, message, flags) from
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* stdin, attempts to perform a signature using the security key provider
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* and returns the resultant signature via stdout.
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*
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* In the future, this program might gain additional functions to support
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* FIDO2 tokens such as enumerating resident keys. When this happens it will
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* be necessary to crank SSH_SK_HELPER_VERSION below.
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*/
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#include "includes.h"
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#include <stdarg.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <errno.h>
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#include "xmalloc.h"
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#include "log.h"
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#include "sshkey.h"
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#include "authfd.h"
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#include "misc.h"
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#include "sshbuf.h"
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#include "msg.h"
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#include "uidswap.h"
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#include "sshkey.h"
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#include "ssherr.h"
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#include "ssh-sk.h"
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#ifdef ENABLE_SK
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extern char *__progname;
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int
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main(int argc, char **argv)
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{
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SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
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LogLevel log_level = SYSLOG_LEVEL_ERROR;
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struct sshbuf *req, *resp, *kbuf;
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struct sshkey *key;
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uint32_t compat;
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const u_char *message;
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u_char version, *sig;
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size_t msglen, siglen;
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char *provider;
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int in, out, ch, r, log_stderr = 0;
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sanitise_stdfd();
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log_init(__progname, log_level, log_facility, log_stderr);
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while ((ch = getopt(argc, argv, "v")) != -1) {
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switch (ch) {
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case 'v':
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log_stderr = 1;
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if (log_level == SYSLOG_LEVEL_ERROR)
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log_level = SYSLOG_LEVEL_DEBUG1;
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else if (log_level < SYSLOG_LEVEL_DEBUG3)
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log_level++;
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break;
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default:
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fprintf(stderr, "usage: %s [-v]\n", __progname);
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exit(1);
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}
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}
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log_init(__progname, log_level, log_facility, log_stderr);
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/*
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* Rearrange our file descriptors a little; we don't trust the
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* providers not to fiddle with stdin/out.
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*/
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closefrom(STDERR_FILENO + 1);
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if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1)
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fatal("%s: dup: %s", __progname, strerror(errno));
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close(STDIN_FILENO);
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close(STDOUT_FILENO);
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sanitise_stdfd(); /* resets to /dev/null */
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if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL)
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fatal("%s: sshbuf_new failed", __progname);
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if (ssh_msg_recv(in, req) < 0)
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fatal("ssh_msg_recv failed");
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close(in);
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debug("%s: received message len %zu", __progname, sshbuf_len(req));
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if ((r = sshbuf_get_u8(req, &version)) != 0)
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fatal("%s: buffer error: %s", __progname, ssh_err(r));
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if (version != SSH_SK_HELPER_VERSION) {
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fatal("unsupported version: received %d, expected %d",
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version, SSH_SK_HELPER_VERSION);
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}
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if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
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(r = sshkey_private_deserialize(kbuf, &key)) != 0)
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fatal("Unable to parse key: %s", ssh_err(r));
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if (sshkey_type_plain(key->type) != KEY_ECDSA_SK)
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fatal("Unsupported key type %s", sshkey_ssh_name(key));
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if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
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(r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
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(r = sshbuf_get_u32(req, &compat)) != 0)
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fatal("%s: buffer error: %s", __progname, ssh_err(r));
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if (sshbuf_len(req) != 0)
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fatal("%s: trailing data in request", __progname);
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debug("%s: ready to sign with key %s, provider %s: "
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"msg len %zu, compat 0x%lx", __progname, sshkey_type(key),
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provider, msglen, (u_long)compat);
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if ((r = sshsk_ecdsa_sign(provider, key, &sig, &siglen,
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message, msglen, compat)) != 0)
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fatal("Signing failed: %s", ssh_err(r));
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/* send reply */
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if ((r = sshbuf_put_string(resp, sig, siglen)) != 0)
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fatal("%s: buffer error: %s", __progname, ssh_err(r));
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debug("%s: reply len %zu", __progname, sshbuf_len(resp));
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if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1)
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fatal("ssh_msg_send failed");
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close(out);
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return (0);
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}
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#else /* ENABLE_SK */
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#include <stdio.h>
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int
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main(int argc, char **argv)
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{
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fprintf(stderr, "ssh-sk-helper: disabled at compile time\n");
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return -1;
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}
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#endif /* ENABLE_SK */
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