/* $OpenBSD: ssh-sk-client.c,v 1.13 2025/02/18 08:02:48 djm 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.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>

#include <fcntl.h>
#include <limits.h>
#include <errno.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "log.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "sshkey.h"
#include "msg.h"
#include "digest.h"
#include "pathnames.h"
#include "ssh-sk.h"
#include "misc.h"

/* #define DEBUG_SK 1 */

static int
start_helper(int *fdp, pid_t *pidp, void (**osigchldp)(int))
{
        void (*osigchld)(int);
        int oerrno, pair[2];
        pid_t pid;
        char *helper, *verbosity = NULL;

        *fdp = -1;
        *pidp = 0;
        *osigchldp = SIG_DFL;

        helper = getenv("SSH_SK_HELPER");
        if (helper == NULL || strlen(helper) == 0)
                helper = _PATH_SSH_SK_HELPER;
        if (access(helper, X_OK) != 0) {
                oerrno = errno;
                error_f("helper \"%s\" unusable: %s", helper, strerror(errno));
                errno = oerrno;
                return SSH_ERR_SYSTEM_ERROR;
        }
#ifdef DEBUG_SK
        verbosity = "-vvv";
#endif

        /* Start helper */
        if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
                error("socketpair: %s", strerror(errno));
                return SSH_ERR_SYSTEM_ERROR;
        }
        osigchld = ssh_signal(SIGCHLD, SIG_DFL);
        if ((pid = fork()) == -1) {
                oerrno = errno;
                error("fork: %s", strerror(errno));
                close(pair[0]);
                close(pair[1]);
                ssh_signal(SIGCHLD, osigchld);
                errno = oerrno;
                return SSH_ERR_SYSTEM_ERROR;
        }
        if (pid == 0) {
                if ((dup2(pair[1], STDIN_FILENO) == -1) ||
                    (dup2(pair[1], STDOUT_FILENO) == -1)) {
                        error_f("dup2: %s", strerror(errno));
                        _exit(1);
                }
                close(pair[0]);
                close(pair[1]);
                closefrom(STDERR_FILENO + 1);
                debug_f("starting %s %s", helper,
                    verbosity == NULL ? "" : verbosity);
                execlp(helper, helper, verbosity, (char *)NULL);
                error_f("execlp: %s", strerror(errno));
                _exit(1);
        }
        close(pair[1]);

        /* success */
        debug3_f("started pid=%ld", (long)pid);
        *fdp = pair[0];
        *pidp = pid;
        *osigchldp = osigchld;
        return 0;
}

static int
reap_helper(pid_t pid)
{
        int status, oerrno;

        debug3_f("pid=%ld", (long)pid);

        errno = 0;
        while (waitpid(pid, &status, 0) == -1) {
                if (errno == EINTR) {
                        errno = 0;
                        continue;
                }
                oerrno = errno;
                error_f("waitpid: %s", strerror(errno));
                errno = oerrno;
                return SSH_ERR_SYSTEM_ERROR;
        }
        if (!WIFEXITED(status)) {
                error_f("helper exited abnormally");
                return SSH_ERR_AGENT_FAILURE;
        } else if (WEXITSTATUS(status) != 0) {
                error_f("helper exited with non-zero exit status");
                return SSH_ERR_AGENT_FAILURE;
        }
        return 0;
}

static int
client_converse(struct sshbuf *msg, struct sshbuf **respp, u_int type)
{
        int oerrno, fd, r2, ll, r = SSH_ERR_INTERNAL_ERROR;
        u_int rtype, rerr;
        pid_t pid;
        u_char version;
        void (*osigchld)(int);
        struct sshbuf *req = NULL, *resp = NULL;
        *respp = NULL;

        if ((r = start_helper(&fd, &pid, &osigchld)) != 0)
                return r;

        if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }
        /* Request preamble: type, log_on_stderr, log_level */
        ll = log_level_get();
        if ((r = sshbuf_put_u32(req, type)) != 0 ||
            (r = sshbuf_put_u8(req, log_is_on_stderr() != 0)) != 0 ||
            (r = sshbuf_put_u32(req, ll < 0 ? 0 : ll)) != 0 ||
            (r = sshbuf_putb(req, msg)) != 0) {
                error_fr(r, "compose");
                goto out;
        }
        if ((r = ssh_msg_send(fd, SSH_SK_HELPER_VERSION, req)) != 0) {
                error_fr(r, "send");
                goto out;
        }
        if ((r = ssh_msg_recv(fd, resp)) != 0) {
                error_fr(r, "receive");
                goto out;
        }
        if ((r = sshbuf_get_u8(resp, &version)) != 0) {
                error_fr(r, "parse version");
                goto out;
        }
        if (version != SSH_SK_HELPER_VERSION) {
                error_f("unsupported version: got %u, expected %u",
                    version, SSH_SK_HELPER_VERSION);
                r = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if ((r = sshbuf_get_u32(resp, &rtype)) != 0) {
                error_fr(r, "parse message type");
                goto out;
        }
        if (rtype == SSH_SK_HELPER_ERROR) {
                if ((r = sshbuf_get_u32(resp, &rerr)) != 0) {
                        error_fr(r, "parse");
                        goto out;
                }
                debug_f("helper returned error -%u", rerr);
                /* OpenSSH error values are negative; encoded as -err on wire */
                if (rerr == 0 || rerr >= INT_MAX)
                        r = SSH_ERR_INTERNAL_ERROR;
                else
                        r = -(int)rerr;
                goto out;
        } else if (rtype != type) {
                error_f("helper returned incorrect message type %u, "
                    "expecting %u", rtype, type);
                r = SSH_ERR_INTERNAL_ERROR;
                goto out;
        }
        /* success */
        r = 0;
 out:
        oerrno = errno;
        close(fd);
        if ((r2 = reap_helper(pid)) != 0) {
                if (r == 0) {
                        r = r2;
                        oerrno = errno;
                }
        }
        if (r == 0) {
                *respp = resp;
                resp = NULL;
        }
        sshbuf_free(req);
        sshbuf_free(resp);
        ssh_signal(SIGCHLD, osigchld);
        errno = oerrno;
        return r;

}

int
sshsk_sign(const char *provider, struct sshkey *key,
    u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
    u_int compat, const char *pin)
{
        int oerrno, r = SSH_ERR_INTERNAL_ERROR;
        struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;

        *sigp = NULL;
        *lenp = 0;

#ifndef ENABLE_SK
        return SSH_ERR_KEY_TYPE_UNKNOWN;
#endif

        if ((kbuf = sshbuf_new()) == NULL ||
            (req = sshbuf_new()) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }

        if ((r = sshkey_private_serialize(key, kbuf)) != 0) {
                error_fr(r, "encode key");
                goto out;
        }
        if ((r = sshbuf_put_stringb(req, kbuf)) != 0 ||
            (r = sshbuf_put_cstring(req, provider)) != 0 ||
            (r = sshbuf_put_string(req, data, datalen)) != 0 ||
            (r = sshbuf_put_cstring(req, NULL)) != 0 || /* alg */
            (r = sshbuf_put_u32(req, compat)) != 0 ||
            (r = sshbuf_put_cstring(req, pin)) != 0) {
                error_fr(r, "compose");
                goto out;
        }

        if ((r = client_converse(req, &resp, SSH_SK_HELPER_SIGN)) != 0)
                goto out;

        if ((r = sshbuf_get_string(resp, sigp, lenp)) != 0) {
                error_fr(r, "parse signature");
                r = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if (sshbuf_len(resp) != 0) {
                error_f("trailing data in response");
                r = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        /* success */
        r = 0;
 out:
        oerrno = errno;
        if (r != 0) {
                freezero(*sigp, *lenp);
                *sigp = NULL;
                *lenp = 0;
        }
        sshbuf_free(kbuf);
        sshbuf_free(req);
        sshbuf_free(resp);
        errno = oerrno;
        return r;
}

int
sshsk_enroll(int type, const char *provider_path, const char *device,
    const char *application, const char *userid, uint8_t flags,
    const char *pin, struct sshbuf *challenge_buf,
    struct sshkey **keyp, struct sshbuf *attest)
{
        int oerrno, r = SSH_ERR_INTERNAL_ERROR;
        struct sshbuf *kbuf = NULL, *abuf = NULL, *req = NULL, *resp = NULL;
        struct sshkey *key = NULL;

        *keyp = NULL;
        if (attest != NULL)
                sshbuf_reset(attest);

#ifndef ENABLE_SK
        return SSH_ERR_KEY_TYPE_UNKNOWN;
#endif

        if (type < 0)
                return SSH_ERR_INVALID_ARGUMENT;

        if ((abuf = sshbuf_new()) == NULL ||
            (kbuf = sshbuf_new()) == NULL ||
            (req = sshbuf_new()) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }

        if ((r = sshbuf_put_u32(req, (u_int)type)) != 0 ||
            (r = sshbuf_put_cstring(req, provider_path)) != 0 ||
            (r = sshbuf_put_cstring(req, device)) != 0 ||
            (r = sshbuf_put_cstring(req, application)) != 0 ||
            (r = sshbuf_put_cstring(req, userid)) != 0 ||
            (r = sshbuf_put_u8(req, flags)) != 0 ||
            (r = sshbuf_put_cstring(req, pin)) != 0 ||
            (r = sshbuf_put_stringb(req, challenge_buf)) != 0) {
                error_fr(r, "compose");
                goto out;
        }

        if ((r = client_converse(req, &resp, SSH_SK_HELPER_ENROLL)) != 0)
                goto out;

        if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
            (r = sshbuf_get_stringb(resp, abuf)) != 0) {
                error_fr(r, "parse");
                r = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if (sshbuf_len(resp) != 0) {
                error_f("trailing data in response");
                r = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
                error_fr(r, "encode");
                goto out;
        }
        if (attest != NULL && (r = sshbuf_putb(attest, abuf)) != 0) {
                error_fr(r, "encode attestation information");
                goto out;
        }

        /* success */
        r = 0;
        *keyp = key;
        key = NULL;
 out:
        oerrno = errno;
        sshkey_free(key);
        sshbuf_free(kbuf);
        sshbuf_free(abuf);
        sshbuf_free(req);
        sshbuf_free(resp);
        errno = oerrno;
        return r;
}

static void
sshsk_free_resident_key(struct sshsk_resident_key *srk)
{
        if (srk == NULL)
                return;
        sshkey_free(srk->key);
        freezero(srk->user_id, srk->user_id_len);
        free(srk);
}


void
sshsk_free_resident_keys(struct sshsk_resident_key **srks, size_t nsrks)
{
        size_t i;

        if (srks == NULL || nsrks == 0)
                return;

        for (i = 0; i < nsrks; i++)
                sshsk_free_resident_key(srks[i]);
        free(srks);
}

int
sshsk_load_resident(const char *provider_path, const char *device,
    const char *pin, u_int flags, struct sshsk_resident_key ***srksp,
    size_t *nsrksp)
{
        int oerrno, r = SSH_ERR_INTERNAL_ERROR;
        struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
        struct sshkey *key = NULL;
        struct sshsk_resident_key *srk = NULL, **srks = NULL, **tmp;
        u_char *userid = NULL;
        size_t userid_len = 0, nsrks = 0;

        *srksp = NULL;
        *nsrksp = 0;

        if ((kbuf = sshbuf_new()) == NULL ||
            (req = sshbuf_new()) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }

        if ((r = sshbuf_put_cstring(req, provider_path)) != 0 ||
            (r = sshbuf_put_cstring(req, device)) != 0 ||
            (r = sshbuf_put_cstring(req, pin)) != 0 ||
            (r = sshbuf_put_u32(req, flags)) != 0) {
                error_fr(r, "compose");
                goto out;
        }

        if ((r = client_converse(req, &resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
                goto out;

        while (sshbuf_len(resp) != 0) {
                /* key, comment, user_id */
                if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
                    (r = sshbuf_get_cstring(resp, NULL, NULL)) != 0 ||
                    (r = sshbuf_get_string(resp, &userid, &userid_len)) != 0) {
                        error_fr(r, "parse");
                        r = SSH_ERR_INVALID_FORMAT;
                        goto out;
                }
                if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
                        error_fr(r, "decode key");
                        goto out;
                }
                if ((srk = calloc(1, sizeof(*srk))) == NULL) {
                        error_f("calloc failed");
                        r = SSH_ERR_ALLOC_FAIL;
                        goto out;
                }
                srk->key = key;
                key = NULL;
                srk->user_id = userid;
                srk->user_id_len = userid_len;
                userid = NULL;
                userid_len = 0;
                if ((tmp = recallocarray(srks, nsrks, nsrks + 1,
                    sizeof(*srks))) == NULL) {
                        error_f("recallocarray keys failed");
                        r = SSH_ERR_ALLOC_FAIL;
                        goto out;
                }
                debug_f("srks[%zu]: %s %s uidlen %zu", nsrks,
                    sshkey_type(srk->key), srk->key->sk_application,
                    srk->user_id_len);
                srks = tmp;
                srks[nsrks++] = srk;
                srk = NULL;
        }

        /* success */
        r = 0;
        *srksp = srks;
        *nsrksp = nsrks;
        srks = NULL;
        nsrks = 0;
 out:
        oerrno = errno;
        sshsk_free_resident_key(srk);
        sshsk_free_resident_keys(srks, nsrks);
        freezero(userid, userid_len);
        sshkey_free(key);
        sshbuf_free(kbuf);
        sshbuf_free(req);
        sshbuf_free(resp);
        errno = oerrno;
        return r;
}