/* $OpenBSD: doas.c,v 1.99 2024/02/15 18:57:58 tedu Exp $ */
/*
 * Copyright (c) 2015 Ted Unangst <tedu@openbsd.org>
 *
 * 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 <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>

#include <limits.h>
#include <login_cap.h>
#include <bsd_auth.h>
#include <readpassphrase.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <unistd.h>
#include <pwd.h>
#include <grp.h>
#include <syslog.h>
#include <errno.h>
#include <fcntl.h>

#include "doas.h"

static void __dead
usage(void)
{
        fprintf(stderr, "usage: doas [-Lns] [-a style] [-C config] [-u user]"
            " command [arg ...]\n");
        exit(1);
}

static int
parseuid(const char *s, uid_t *uid)
{
        struct passwd *pw;
        const char *errstr;

        if ((pw = getpwnam(s)) != NULL) {
                *uid = pw->pw_uid;
                if (*uid == UID_MAX)
                        return -1;
                return 0;
        }
        *uid = strtonum(s, 0, UID_MAX - 1, &errstr);
        if (errstr)
                return -1;
        return 0;
}

static int
uidcheck(const char *s, uid_t desired)
{
        uid_t uid;

        if (parseuid(s, &uid) != 0)
                return -1;
        if (uid != desired)
                return -1;
        return 0;
}

static int
parsegid(const char *s, gid_t *gid)
{
        struct group *gr;
        const char *errstr;

        if ((gr = getgrnam(s)) != NULL) {
                *gid = gr->gr_gid;
                if (*gid == GID_MAX)
                        return -1;
                return 0;
        }
        *gid = strtonum(s, 0, GID_MAX - 1, &errstr);
        if (errstr)
                return -1;
        return 0;
}

static int
match(uid_t uid, gid_t *groups, int ngroups, uid_t target, const char *cmd,
    const char **cmdargs, struct rule *r)
{
        int i;

        if (r->ident[0] == ':') {
                gid_t rgid;
                if (parsegid(r->ident + 1, &rgid) == -1)
                        return 0;
                for (i = 0; i < ngroups; i++) {
                        if (rgid == groups[i])
                                break;
                }
                if (i == ngroups)
                        return 0;
        } else {
                if (uidcheck(r->ident, uid) != 0)
                        return 0;
        }
        if (r->target && uidcheck(r->target, target) != 0)
                return 0;
        if (r->cmd) {
                if (strcmp(r->cmd, cmd))
                        return 0;
                if (r->cmdargs) {
                        /* if arguments were given, they should match explicitly */
                        for (i = 0; r->cmdargs[i]; i++) {
                                if (!cmdargs[i])
                                        return 0;
                                if (strcmp(r->cmdargs[i], cmdargs[i]))
                                        return 0;
                        }
                        if (cmdargs[i])
                                return 0;
                }
        }
        return 1;
}

static int
permit(uid_t uid, gid_t *groups, int ngroups, const struct rule **lastr,
    uid_t target, const char *cmd, const char **cmdargs)
{
        size_t i;

        *lastr = NULL;
        for (i = 0; i < nrules; i++) {
                if (match(uid, groups, ngroups, target, cmd,
                    cmdargs, rules[i]))
                        *lastr = rules[i];
        }
        if (!*lastr)
                return -1;
        if ((*lastr)->action == PERMIT)
                return 0;
        return -1;
}

static void
parseconfig(const char *filename, int checkperms)
{
        extern FILE *yyfp;
        extern int yyparse(void);
        struct stat sb;

        yyfp = fopen(filename, "r");
        if (!yyfp)
                err(1, checkperms ? "doas is not enabled, %s" :
                    "could not open config file %s", filename);

        if (checkperms) {
                if (fstat(fileno(yyfp), &sb) != 0)
                        err(1, "fstat(\"%s\")", filename);
                if ((sb.st_mode & (S_IWGRP|S_IWOTH)) != 0)
                        errx(1, "%s is writable by group or other", filename);
                if (sb.st_uid != 0)
                        errx(1, "%s is not owned by root", filename);
        }

        yyparse();
        fclose(yyfp);
        if (parse_error)
                exit(1);
}

static void __dead
checkconfig(const char *confpath, int argc, char **argv,
    uid_t uid, gid_t *groups, int ngroups, uid_t target)
{
        const struct rule *rule;
        int rv;

        setresuid(uid, uid, uid);
        if (pledge("stdio rpath getpw", NULL) == -1)
                err(1, "pledge");
        parseconfig(confpath, 0);
        if (!argc)
                exit(0);
        rv = permit(uid, groups, ngroups, &rule, target, argv[0],
            (const char **)argv + 1);
        if (rv == 0) {
                printf("permit%s\n", (rule->options & NOPASS) ? " nopass" : "");
                exit(0);
        } else {
                printf("deny\n");
                exit(1);
        }
}

static int
authuser_checkpass(char *myname, char *login_style)
{
        char *challenge = NULL, *response, rbuf[1024], cbuf[128];
        auth_session_t *as;

        if (!(as = auth_userchallenge(myname, login_style, "auth-doas",
            &challenge))) {
                warnx("Authentication failed");
                return AUTH_FAILED;
        }
        if (!challenge) {
                char host[HOST_NAME_MAX + 1];

                if (gethostname(host, sizeof(host)))
                        snprintf(host, sizeof(host), "?");
                snprintf(cbuf, sizeof(cbuf),
                    "\rdoas (%.32s@%.32s) password: ", myname, host);
                challenge = cbuf;
        }
        response = readpassphrase(challenge, rbuf, sizeof(rbuf),
            RPP_REQUIRE_TTY);
        if (response == NULL && errno == ENOTTY) {
                syslog(LOG_AUTHPRIV | LOG_NOTICE,
                    "tty required for %s", myname);
                errx(1, "a tty is required");
        }
        if (!auth_userresponse(as, response, 0)) {
                explicit_bzero(rbuf, sizeof(rbuf));
                syslog(LOG_AUTHPRIV | LOG_NOTICE,
                    "failed auth for %s", myname);
                warnx("Authentication failed");
                return AUTH_FAILED;
        }
        explicit_bzero(rbuf, sizeof(rbuf));
        return AUTH_OK;
}

static void
authuser(char *myname, char *login_style, int persist)
{
        int i, fd = -1;

        if (persist)
                fd = open("/dev/tty", O_RDWR);
        if (fd != -1) {
                if (ioctl(fd, TIOCCHKVERAUTH) == 0)
                        goto good;
        }
        for (i = 0; i < AUTH_RETRIES; i++) {
                if (authuser_checkpass(myname, login_style) == AUTH_OK)
                        goto good;
        }
        exit(1);
good:
        if (fd != -1) {
                int secs = 5 * 60;
                ioctl(fd, TIOCSETVERAUTH, &secs);
                close(fd);
        }
}

int
unveilcommands(const char *ipath, const char *cmd)
{
        char *path = NULL, *p;
        int unveils = 0;

        if (strchr(cmd, '/') != NULL) {
                if (unveil(cmd, "x") != -1)
                        unveils++;
                goto done;
        }

        if (!ipath) {
                errno = ENOENT;
                goto done;
        }
        path = strdup(ipath);
        if (!path) {
                errno = ENOENT;
                goto done;
        }
        for (p = path; p && *p; ) {
                char buf[PATH_MAX];
                char *cp = strsep(&p, ":");

                if (cp) {
                        int r = snprintf(buf, sizeof buf, "%s/%s", cp, cmd);
                        if (r >= 0 && r < sizeof buf) {
                                if (unveil(buf, "x") != -1)
                                        unveils++;
                        }
                }
        }
done:
        free(path);
        return (unveils);
}

int
main(int argc, char **argv)
{
        const char *safepath = "/bin:/sbin:/usr/bin:/usr/sbin:"
            "/usr/local/bin:/usr/local/sbin";
        const char *confpath = NULL;
        char *shargv[] = { NULL, NULL };
        char *sh;
        const char *p;
        const char *cmd;
        char cmdline[LINE_MAX];
        char mypwbuf[_PW_BUF_LEN], targpwbuf[_PW_BUF_LEN];
        struct passwd mypwstore, targpwstore;
        struct passwd *mypw, *targpw;
        const struct rule *rule;
        uid_t uid;
        uid_t target = 0;
        gid_t groups[NGROUPS_MAX + 1];
        int ngroups;
        int i, ch, rv;
        int sflag = 0;
        int nflag = 0;
        char cwdpath[PATH_MAX];
        const char *cwd;
        char *login_style = NULL;
        char **envp;

        setprogname("doas");

        closefrom(STDERR_FILENO + 1);

        uid = getuid();

        while ((ch = getopt(argc, argv, "a:C:Lnsu:")) != -1) {
                switch (ch) {
                case 'a':
                        login_style = optarg;
                        break;
                case 'C':
                        confpath = optarg;
                        break;
                case 'L':
                        i = open("/dev/tty", O_RDWR);
                        if (i != -1)
                                ioctl(i, TIOCCLRVERAUTH);
                        exit(i == -1);
                case 'u':
                        if (parseuid(optarg, &target) != 0)
                                errx(1, "unknown user");
                        break;
                case 'n':
                        nflag = 1;
                        break;
                case 's':
                        sflag = 1;
                        break;
                default:
                        usage();
                        break;
                }
        }
        argv += optind;
        argc -= optind;

        if (confpath) {
                if (sflag)
                        usage();
        } else if ((!sflag && !argc) || (sflag && argc))
                usage();

        rv = getpwuid_r(uid, &mypwstore, mypwbuf, sizeof(mypwbuf), &mypw);
        if (rv != 0)
                err(1, "getpwuid_r failed");
        if (mypw == NULL)
                errx(1, "no passwd entry for self");
        ngroups = getgroups(NGROUPS_MAX, groups);
        if (ngroups == -1)
                err(1, "can't get groups");
        groups[ngroups++] = getgid();

        if (sflag) {
                sh = getenv("SHELL");
                if (sh == NULL || *sh == '\0') {
                        shargv[0] = mypw->pw_shell;
                } else
                        shargv[0] = sh;
                argv = shargv;
                argc = 1;
        }

        if (confpath) {
                if (pledge("stdio rpath getpw id", NULL) == -1)
                        err(1, "pledge");
                checkconfig(confpath, argc, argv, uid, groups, ngroups,
                    target);
                exit(1);        /* fail safe */
        }

        if (geteuid())
                errx(1, "not installed setuid");

        parseconfig("/etc/doas.conf", 1);

        /* cmdline is used only for logging, no need to abort on truncate */
        (void)strlcpy(cmdline, argv[0], sizeof(cmdline));
        for (i = 1; i < argc; i++) {
                if (strlcat(cmdline, " ", sizeof(cmdline)) >= sizeof(cmdline))
                        break;
                if (strlcat(cmdline, argv[i], sizeof(cmdline)) >= sizeof(cmdline))
                        break;
        }

        cmd = argv[0];
        rv = permit(uid, groups, ngroups, &rule, target, cmd,
            (const char **)argv + 1);
        if (rv != 0) {
                syslog(LOG_AUTHPRIV | LOG_NOTICE,
                    "command not permitted for %s: %s", mypw->pw_name, cmdline);
                errc(1, EPERM, NULL);
        }

        if (!(rule->options & NOPASS)) {
                if (nflag)
                        errx(1, "Authentication required");

                authuser(mypw->pw_name, login_style, rule->options & PERSIST);
        }

        if ((p = getenv("PATH")) != NULL)
                formerpath = strdup(p);
        if (formerpath == NULL)
                formerpath = "";

        if (unveil(_PATH_LOGIN_CONF, "r") == -1)
                err(1, "unveil %s", _PATH_LOGIN_CONF);
        if (unveil(_PATH_LOGIN_CONF ".db", "r") == -1)
                err(1, "unveil %s.db", _PATH_LOGIN_CONF);
        if (unveil(_PATH_LOGIN_CONF_D, "r") == -1)
                err(1, "unveil %s", _PATH_LOGIN_CONF_D);
        if (rule->cmd) {
                if (setenv("PATH", safepath, 1) == -1)
                        err(1, "failed to set PATH '%s'", safepath);
        }
        if (unveilcommands(getenv("PATH"), cmd) == 0)
                goto fail;

        if (pledge("stdio rpath getpw exec id", NULL) == -1)
                err(1, "pledge");

        rv = getpwuid_r(target, &targpwstore, targpwbuf, sizeof(targpwbuf), &targpw);
        if (rv != 0)
                err(1, "getpwuid_r failed");
        if (targpw == NULL)
                errx(1, "no passwd entry for target");

        if (setusercontext(NULL, targpw, target, LOGIN_SETGROUP |
            LOGIN_SETPATH |
            LOGIN_SETPRIORITY | LOGIN_SETRESOURCES | LOGIN_SETUMASK |
            LOGIN_SETUSER | LOGIN_SETENV | LOGIN_SETRTABLE) != 0)
                errx(1, "failed to set user context for target");

        if (pledge("stdio rpath exec", NULL) == -1)
                err(1, "pledge");

        if (getcwd(cwdpath, sizeof(cwdpath)) == NULL)
                cwd = "(failed)";
        else
                cwd = cwdpath;

        if (pledge("stdio exec", NULL) == -1)
                err(1, "pledge");

        if (!(rule->options & NOLOG)) {
                syslog(LOG_AUTHPRIV | LOG_INFO,
                    "%s ran command %s as %s from %s",
                    mypw->pw_name, cmdline, targpw->pw_name, cwd);
        }

        envp = prepenv(rule, mypw, targpw);

        /* setusercontext set path for the next process, so reset it for us */
        if (rule->cmd) {
                if (setenv("PATH", safepath, 1) == -1)
                        err(1, "failed to set PATH '%s'", safepath);
        } else {
                if (setenv("PATH", formerpath, 1) == -1)
                        err(1, "failed to set PATH '%s'", formerpath);
        }
        execvpe(cmd, argv, envp);
fail:
        if (errno == ENOENT)
                errx(1, "%s: command not found", cmd);
        err(1, "%s", cmd);
}