/* $OpenBSD: ssh-sk-helper.c,v 1.14 2022/12/04 11:03:11 dtucker 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 operations for
 * security keys are stateless.
 *
 * Please crank SSH_SK_HELPER_VERSION in sshkey.h for any incompatible
 * protocol changes.
 */
 
#include "includes.h"

#include <limits.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 "ssherr.h"
#include "ssh-sk.h"

#ifdef ENABLE_SK
extern char *__progname;

static struct sshbuf *reply_error(int r, char *fmt, ...)
    __attribute__((__format__ (printf, 2, 3)));

static struct sshbuf *
reply_error(int r, char *fmt, ...)
{
        char *msg;
        va_list ap;
        struct sshbuf *resp;

        va_start(ap, fmt);
        xvasprintf(&msg, fmt, ap);
        va_end(ap);
        debug("%s: %s", __progname, msg);
        free(msg);

        if (r >= 0)
                fatal_f("invalid error code %d", r);

        if ((resp = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new failed", __progname);
        if (sshbuf_put_u32(resp, SSH_SK_HELPER_ERROR) != 0 ||
            sshbuf_put_u32(resp, (u_int)-r) != 0)
                fatal("%s: buffer error", __progname);
        return resp;
}

/* If the specified string is zero length, then free it and replace with NULL */
static void
null_empty(char **s)
{
        if (s == NULL || *s == NULL || **s != '\0')
                return;

        free(*s);
        *s = NULL;
}

static struct sshbuf *
process_sign(struct sshbuf *req)
{
        int r = SSH_ERR_INTERNAL_ERROR;
        struct sshbuf *resp, *kbuf;
        struct sshkey *key = NULL;
        uint32_t compat;
        const u_char *message;
        u_char *sig = NULL;
        size_t msglen, siglen = 0;
        char *provider = NULL, *pin = NULL;

        if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
            (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
            (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
            (r = sshbuf_get_cstring(req, NULL, NULL)) != 0 || /* alg */
            (r = sshbuf_get_u32(req, &compat)) != 0 ||
            (r = sshbuf_get_cstring(req, &pin, NULL)) != 0)
                fatal_r(r, "%s: parse", __progname);
        if (sshbuf_len(req) != 0)
                fatal("%s: trailing data in request", __progname);

        if ((r = sshkey_private_deserialize(kbuf, &key)) != 0)
                fatal_r(r, "%s: Unable to parse private key", __progname);
        if (!sshkey_is_sk(key)) {
                fatal("%s: Unsupported key type %s",
                    __progname, sshkey_ssh_name(key));
        }

        debug_f("ready to sign with key %s, provider %s: "
            "msg len %zu, compat 0x%lx", sshkey_type(key),
            provider, msglen, (u_long)compat);

        null_empty(&pin);

        if ((r = sshsk_sign(provider, key, &sig, &siglen,
            message, msglen, compat, pin)) != 0) {
                resp = reply_error(r, "Signing failed: %s", ssh_err(r));
                goto out;
        }

        if ((resp = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new failed", __progname);

        if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_SIGN)) != 0 ||
            (r = sshbuf_put_string(resp, sig, siglen)) != 0)
                fatal_r(r, "%s: compose", __progname);
 out:
        sshkey_free(key);
        sshbuf_free(kbuf);
        free(provider);
        if (sig != NULL)
                freezero(sig, siglen);
        if (pin != NULL)
                freezero(pin, strlen(pin));
        return resp;
}

static struct sshbuf *
process_enroll(struct sshbuf *req)
{
        int r;
        u_int type;
        char *provider, *application, *pin, *device, *userid;
        uint8_t flags;
        struct sshbuf *challenge, *attest, *kbuf, *resp;
        struct sshkey *key;

        if ((attest = sshbuf_new()) == NULL ||
            (kbuf = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new failed", __progname);

        if ((r = sshbuf_get_u32(req, &type)) != 0 ||
            (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
            (r = sshbuf_get_cstring(req, &device, NULL)) != 0 ||
            (r = sshbuf_get_cstring(req, &application, NULL)) != 0 ||
            (r = sshbuf_get_cstring(req, &userid, NULL)) != 0 ||
            (r = sshbuf_get_u8(req, &flags)) != 0 ||
            (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 ||
            (r = sshbuf_froms(req, &challenge)) != 0)
                fatal_r(r, "%s: parse", __progname);
        if (sshbuf_len(req) != 0)
                fatal("%s: trailing data in request", __progname);

        if (type > INT_MAX)
                fatal("%s: bad type %u", __progname, type);
        if (sshbuf_len(challenge) == 0) {
                sshbuf_free(challenge);
                challenge = NULL;
        }
        null_empty(&device);
        null_empty(&userid);
        null_empty(&pin);

        if ((r = sshsk_enroll((int)type, provider, device, application, userid,
            flags, pin, challenge, &key, attest)) != 0) {
                resp = reply_error(r, "Enrollment failed: %s", ssh_err(r));
                goto out;
        }

        if ((resp = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new failed", __progname);
        if ((r = sshkey_private_serialize(key, kbuf)) != 0)
                fatal_r(r, "%s: encode key", __progname);
        if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_ENROLL)) != 0 ||
            (r = sshbuf_put_stringb(resp, kbuf)) != 0 ||
            (r = sshbuf_put_stringb(resp, attest)) != 0)
                fatal_r(r, "%s: compose", __progname);

 out:
        sshkey_free(key);
        sshbuf_free(kbuf);
        sshbuf_free(attest);
        sshbuf_free(challenge);
        free(provider);
        free(application);
        if (pin != NULL)
                freezero(pin, strlen(pin));

        return resp;
}

static struct sshbuf *
process_load_resident(struct sshbuf *req)
{
        int r;
        char *provider, *pin, *device;
        struct sshbuf *kbuf, *resp;
        struct sshsk_resident_key **srks = NULL;
        size_t nsrks = 0, i;
        u_int flags;

        if ((kbuf = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new failed", __progname);

        if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
            (r = sshbuf_get_cstring(req, &device, NULL)) != 0 ||
            (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 ||
            (r = sshbuf_get_u32(req, &flags)) != 0)
                fatal_r(r, "%s: parse", __progname);
        if (sshbuf_len(req) != 0)
                fatal("%s: trailing data in request", __progname);

        null_empty(&device);
        null_empty(&pin);

        if ((r = sshsk_load_resident(provider, device, pin, flags,
            &srks, &nsrks)) != 0) {
                resp = reply_error(r, "sshsk_load_resident failed: %s",
                    ssh_err(r));
                goto out;
        }

        if ((resp = sshbuf_new()) == NULL)
                fatal("%s: sshbuf_new failed", __progname);

        if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
                fatal_r(r, "%s: compose", __progname);

        for (i = 0; i < nsrks; i++) {
                debug_f("key %zu %s %s uidlen %zu", i,
                    sshkey_type(srks[i]->key), srks[i]->key->sk_application,
                    srks[i]->user_id_len);
                sshbuf_reset(kbuf);
                if ((r = sshkey_private_serialize(srks[i]->key, kbuf)) != 0)
                        fatal_r(r, "%s: encode key", __progname);
                if ((r = sshbuf_put_stringb(resp, kbuf)) != 0 ||
                    (r = sshbuf_put_cstring(resp, "")) != 0 || /* comment */
                    (r = sshbuf_put_string(resp, srks[i]->user_id,
                    srks[i]->user_id_len)) != 0)
                        fatal_r(r, "%s: compose key", __progname);
        }

 out:
        sshsk_free_resident_keys(srks, nsrks);
        sshbuf_free(kbuf);
        free(provider);
        free(device);
        if (pin != NULL)
                freezero(pin, strlen(pin));
        return resp;
}

int
main(int argc, char **argv)
{
        SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
        LogLevel log_level = SYSLOG_LEVEL_ERROR;
        struct sshbuf *req, *resp;
        int in, out, ch, r, vflag = 0;
        u_int rtype, ll = 0;
        uint8_t version, 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':
                        vflag = 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, vflag);

        /*
         * 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)
                fatal("%s: sshbuf_new failed", __progname);
        if (ssh_msg_recv(in, req) < 0)
                fatal("ssh_msg_recv failed");
        close(in);
        debug_f("received message len %zu", sshbuf_len(req));

        if ((r = sshbuf_get_u8(req, &version)) != 0)
                fatal_r(r, "%s: parse version", __progname);
        if (version != SSH_SK_HELPER_VERSION) {
                fatal("unsupported version: received %d, expected %d",
                    version, SSH_SK_HELPER_VERSION);
        }

        if ((r = sshbuf_get_u32(req, &rtype)) != 0 ||
            (r = sshbuf_get_u8(req, &log_stderr)) != 0 ||
            (r = sshbuf_get_u32(req, &ll)) != 0)
                fatal_r(r, "%s: parse", __progname);

        if (!vflag && log_level_name((LogLevel)ll) != NULL)
                log_init(__progname, (LogLevel)ll, log_facility, log_stderr);

        switch (rtype) {
        case SSH_SK_HELPER_SIGN:
                resp = process_sign(req);
                break;
        case SSH_SK_HELPER_ENROLL:
                resp = process_enroll(req);
                break;
        case SSH_SK_HELPER_LOAD_RESIDENT:
                resp = process_load_resident(req);
                break;
        default:
                fatal("%s: unsupported request type %u", __progname, rtype);
        }
        sshbuf_free(req);
        debug_f("reply len %zu", sshbuf_len(resp));

        if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1)
                fatal("ssh_msg_send failed");
        sshbuf_free(resp);
        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 */