/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/types.h>
#include <sys/capsicum.h>
#include <sys/file.h>
#include <sys/stat.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <libutil.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

struct pidfh {
        int     pf_dirfd;
        int     pf_fd;
        char    pf_dir[MAXPATHLEN + 1];
        char    pf_filename[MAXPATHLEN + 1];
        dev_t   pf_dev;
        ino_t   pf_ino;
};

static int _pidfile_remove(struct pidfh *pfh, int freeit);

static int
pidfile_verify(const struct pidfh *pfh)
{
        struct stat sb;

        if (pfh == NULL || pfh->pf_fd == -1)
                return (EDOOFUS);
        /*
         * Check remembered descriptor.
         */
        if (fstat(pfh->pf_fd, &sb) == -1)
                return (errno);
        if (sb.st_dev != pfh->pf_dev || sb.st_ino != pfh->pf_ino)
                return (EDOOFUS);
        return (0);
}

static int
pidfile_read_impl(int dirfd, const char *filename, pid_t *pidptr)
{
        char buf[16], *endptr;
        int error, fd, i;

        fd = openat(dirfd, filename, O_RDONLY | O_CLOEXEC);
        if (fd == -1)
                return (errno);

        i = read(fd, buf, sizeof(buf) - 1);
        error = errno;  /* Remember errno in case close() wants to change it. */
        close(fd);
        if (i == -1)
                return (error);
        else if (i == 0)
                return (EAGAIN);
        buf[i] = '\0';

        *pidptr = strtol(buf, &endptr, 10);
        if (endptr != &buf[i])
                return (EINVAL);

        return (0);
}

static int
pidfile_read(int dirfd, const char *filename, pid_t *pidptr)
{
        struct timespec rqtp;
        int count;

        count = 20;
        rqtp.tv_sec = 0;
        rqtp.tv_nsec = 5000000;
        for (;;) {
                errno = pidfile_read_impl(dirfd, filename, pidptr);
                if (errno != EAGAIN || --count == 0)
                        break;
                nanosleep(&rqtp, 0);
        }
        if (errno == EAGAIN)
                *pidptr = -1;
        return (errno);
}

struct pidfh *
pidfile_open(const char *pathp, mode_t mode, pid_t *pidptr)
{
        char path[MAXPATHLEN];
        struct pidfh *pfh;
        struct stat sb;
        int error, fd, dirfd, dirlen, filenamelen;
        cap_rights_t caprights;

        pfh = malloc(sizeof(*pfh));
        if (pfh == NULL)
                return (NULL);

        if (pathp == NULL) {
                dirlen = snprintf(pfh->pf_dir, sizeof(pfh->pf_dir),
                    "/var/run/");
                filenamelen = snprintf(pfh->pf_filename,
                    sizeof(pfh->pf_filename), "%s.pid", getprogname());
        } else {
                if (strlcpy(path, pathp, sizeof(path)) >= sizeof(path)) {
                        free(pfh);
                        errno = ENAMETOOLONG;
                        return (NULL);
                }
                dirlen = strlcpy(pfh->pf_dir, dirname(path),
                    sizeof(pfh->pf_dir));
                (void)strlcpy(path, pathp, sizeof(path));
                filenamelen = strlcpy(pfh->pf_filename, basename(path),
                    sizeof(pfh->pf_filename));
        }

        if (dirlen >= (int)sizeof(pfh->pf_dir) ||
            filenamelen >= (int)sizeof(pfh->pf_filename)) {
                free(pfh);
                errno = ENAMETOOLONG;
                return (NULL);
        }

        dirfd = open(pfh->pf_dir, O_CLOEXEC | O_DIRECTORY | O_NONBLOCK);
        if (dirfd == -1) {
                error = errno;
                free(pfh);
                errno = error;
                return (NULL);
        }

        /*
         * Open the PID file and obtain exclusive lock.
         * We truncate PID file here only to remove old PID immediately,
         * PID file will be truncated again in pidfile_write(), so
         * pidfile_write() can be called multiple times.
         */
        fd = flopenat(dirfd, pfh->pf_filename,
            O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_NONBLOCK, mode);
        if (fd == -1) {
                if (errno == EWOULDBLOCK) {
                        if (pidptr == NULL) {
                                errno = EEXIST;
                        } else {
                                errno = pidfile_read(dirfd,
                                    pfh->pf_filename, pidptr);
                                if (errno == 0 || errno == EAGAIN)
                                        errno = EEXIST;
                        }
                }
                error = errno;
                close(dirfd);
                free(pfh);
                errno = error;
                return (NULL);
        }

        /*
         * Remember file information, so in pidfile_write() we are sure we write
         * to the proper descriptor.
         */
        if (fstat(fd, &sb) == -1) {
                goto failed;
        }

        if (cap_rights_limit(dirfd,
            cap_rights_init(&caprights, CAP_UNLINKAT)) < 0 && errno != ENOSYS) {
                goto failed;
        }

        if (cap_rights_limit(fd, cap_rights_init(&caprights, CAP_PWRITE,
            CAP_FSTAT, CAP_FTRUNCATE, CAP_EVENT)) < 0 &&
            errno != ENOSYS) {
                goto failed;
        }

        pfh->pf_dirfd = dirfd;
        pfh->pf_fd = fd;
        pfh->pf_dev = sb.st_dev;
        pfh->pf_ino = sb.st_ino;

        return (pfh);

failed:
        error = errno;
        unlinkat(dirfd, pfh->pf_filename, 0);
        close(dirfd);
        close(fd);
        free(pfh);
        errno = error;
        return (NULL);
}

int
pidfile_write(struct pidfh *pfh)
{
        char pidstr[16];
        int error, fd;

        /*
         * Check remembered descriptor, so we don't overwrite some other
         * file if pidfile was closed and descriptor reused.
         */
        errno = pidfile_verify(pfh);
        if (errno != 0) {
                /*
                 * Don't close descriptor, because we are not sure if it's ours.
                 */
                return (-1);
        }
        fd = pfh->pf_fd;

        /*
         * Truncate PID file, so multiple calls of pidfile_write() are allowed.
         */
        if (ftruncate(fd, 0) == -1) {
                error = errno;
                _pidfile_remove(pfh, 0);
                errno = error;
                return (-1);
        }

        snprintf(pidstr, sizeof(pidstr), "%u", getpid());
        if (pwrite(fd, pidstr, strlen(pidstr), 0) != (ssize_t)strlen(pidstr)) {
                error = errno;
                _pidfile_remove(pfh, 0);
                errno = error;
                return (-1);
        }

        return (0);
}

int
pidfile_close(struct pidfh *pfh)
{
        int error;

        error = pidfile_verify(pfh);
        if (error != 0) {
                errno = error;
                return (-1);
        }

        if (close(pfh->pf_fd) == -1)
                error = errno;
        if (close(pfh->pf_dirfd) == -1 && error == 0)
                error = errno;

        free(pfh);
        if (error != 0) {
                errno = error;
                return (-1);
        }
        return (0);
}

static int
_pidfile_remove(struct pidfh *pfh, int freeit)
{
        int error;

        error = pidfile_verify(pfh);
        if (error != 0) {
                errno = error;
                return (-1);
        }

        if (funlinkat(pfh->pf_dirfd, pfh->pf_filename, pfh->pf_fd, 0) == -1) {
                if (errno == EDEADLK)
                        return (-1);
                error = errno;
        }
        if (close(pfh->pf_fd) == -1 && error == 0)
                error = errno;
        if (close(pfh->pf_dirfd) == -1 && error == 0)
                error = errno;
        if (freeit)
                free(pfh);
        else
                pfh->pf_fd = -1;
        if (error != 0) {
                errno = error;
                return (-1);
        }
        return (0);
}

int
pidfile_remove(struct pidfh *pfh)
{

        return (_pidfile_remove(pfh, 1));
}

int
pidfile_fileno(const struct pidfh *pfh)
{

        if (pfh == NULL || pfh->pf_fd == -1) {
                errno = EDOOFUS;
                return (-1);
        }
        return (pfh->pf_fd);
}

int
pidfile_signal(const char *pathp, int sig, pid_t *pidptr)
{
        pid_t pid;
        int fd;

        fd = flopenat(AT_FDCWD, pathp,
            O_RDONLY | O_CLOEXEC | O_NONBLOCK);
        if (fd >= 0) {
                /*
                 * The file exists but is not locked,
                 * so the daemon is dead. Nothing to do.
                 */
                close(fd);
                errno = ENOENT;
                return (errno);
        }
        if (errno != EWOULDBLOCK) {
                return (errno);
        }
        errno = pidfile_read(AT_FDCWD, pathp, &pid);
        if (errno != 0)
                return (errno);
        /*
         * Refuse to send broadcast or group signals, this has
         * happened due to the bugs in pidfile(3).
         */
        if (pid <= 0)
                return (EDOM);
        kill(pid, sig);
        if (pidptr != NULL)
                *pidptr = pid;
        return (errno);
}