named/unix/os.c

	os.c revision 0c27b3fe77ac1d5094ba3521e8142d9e7973133f
/*
 * Copyright (C) 1999-2002, 2004-2011, 2013-2016  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/*! \file */

#include <config.h>
#include <stdarg.h>

#include <sys/types.h>  /* dev_t FreeBSD 2.1 */
#include <sys/stat.h>
#ifdef HAVE_UNAME
#include <sys/utsname.h>
#endif

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>        /* Required for initgroups() on IRIX. */
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <syslog.h>
#ifdef HAVE_TZSET
#include <time.h>
#endif
#include <unistd.h>

#include <isc/buffer.h>
#include <isc/file.h>
#include <isc/print.h>
#include <isc/resource.h>
#include <isc/result.h>
#include <isc/strerror.h>
#include <isc/string.h>

#include <named/main.h>
#include <named/os.h>
#ifdef HAVE_LIBSCF
#include <named/ns_smf_globals.h>
#endif

static char *pidfile = NULL;
static char *lockfile = NULL;
static int devnullfd = -1;
static int singletonfd = -1;

#ifndef ISC_FACILITY
#define ISC_FACILITY LOG_DAEMON
#endif

/*
 * If there's no <linux/capability.h>, we don't care about <sys/prctl.h>
 */
#ifndef HAVE_LINUX_CAPABILITY_H
#undef HAVE_SYS_PRCTL_H
#endif

/*
 * Linux defines:
 *  (T) HAVE_LINUXTHREADS
 *  (C) HAVE_SYS_CAPABILITY_H (or HAVE_LINUX_CAPABILITY_H)
 *  (P) HAVE_SYS_PRCTL_H
 * The possible cases are:
 *  none:   setuid() normally
 *  T:  no setuid()
 *  C:  setuid() normally, drop caps (keep CAP_SETUID)
 *  T+C:    no setuid(), drop caps (don't keep CAP_SETUID)
 *  T+C+P:  setuid() early, drop caps (keep CAP_SETUID)
 *  C+P:    setuid() normally, drop caps (keep CAP_SETUID)
 *  P:  not possible
 *  T+P:    not possible
 *
 * if (C)
 *  caps = BIND_SERVICE + CHROOT + SETGID
 *  if ((T && C && P) || !T)
 *      caps += SETUID
 *  endif
 *  capset(caps)
 * endif
 * if (T && C && P && -u)
 *  setuid()
 * else if (T && -u)
 *  fail
 * --> start threads
 * if (!T && -u)
 *  setuid()
 * if (C && (P || !-u))
 *  caps = BIND_SERVICE
 *  capset(caps)
 * endif
 *
 * It will be nice when Linux threads work properly with setuid().
 */

#ifdef HAVE_LINUXTHREADS
static pid_t mainpid = 0;
#endif

static struct passwd *runas_pw = NULL;
static isc_boolean_t done_setuid = ISC_FALSE;
static int dfd[2] = { -1, -1 };

#ifdef HAVE_LINUX_CAPABILITY_H

static isc_boolean_t non_root = ISC_FALSE;
static isc_boolean_t non_root_caps = ISC_FALSE;

#ifdef HAVE_SYS_CAPABILITY_H
#include <sys/capability.h>
#else
#ifdef HAVE_LINUX_TYPES_H
#include <linux/types.h>
#endif
/*%
 * We define _LINUX_FS_H to prevent it from being included.  We don't need
 * anything from it, and the files it includes cause warnings with 2.2
 * kernels, and compilation failures (due to conflicts between <linux/string.h>
 * and <string.h>) on 2.3 kernels.
 */
#define _LINUX_FS_H
#include <linux/capability.h>
#include <syscall.h>
#ifndef SYS_capset
#ifndef __NR_capset
#include <asm/unistd.h> /* Slackware 4.0 needs this. */
#endif /* __NR_capset */
#define SYS_capset __NR_capset
#endif /* SYS_capset */
#endif /* HAVE_SYS_CAPABILITY_H */

#ifdef HAVE_SYS_PRCTL_H
#include <sys/prctl.h>      /* Required for prctl(). */

/*
 * If the value of PR_SET_KEEPCAPS is not in <sys/prctl.h>, define it
 * here.  This allows setuid() to work on systems running a new enough
 * kernel but with /usr/include/linux pointing to "standard" kernel
 * headers.
 */
#ifndef PR_SET_KEEPCAPS
#define PR_SET_KEEPCAPS 8
#endif

#endif /* HAVE_SYS_PRCTL_H */

#ifdef HAVE_LIBCAP
#define SETCAPS_FUNC "cap_set_proc "
#else
typedef unsigned int cap_t;
#define SETCAPS_FUNC "syscall(capset) "
#endif /* HAVE_LIBCAP */

static void
linux_setcaps(cap_t caps) {
#ifndef HAVE_LIBCAP
    struct __user_cap_header_struct caphead;
    struct __user_cap_data_struct cap;
#endif
    char strbuf[ISC_STRERRORSIZE];

    if ((getuid() != 0 && !non_root_caps) || non_root)
        return;
#ifndef HAVE_LIBCAP
    memset(&caphead, 0, sizeof(caphead));
    caphead.version = _LINUX_CAPABILITY_VERSION;
    caphead.pid = 0;
    memset(&cap, 0, sizeof(cap));
    cap.effective = caps;
    cap.permitted = caps;
    cap.inheritable = 0;
#endif
#ifdef HAVE_LIBCAP
    if (cap_set_proc(caps) < 0) {
#else
    if (syscall(SYS_capset, &caphead, &cap) < 0) {
#endif
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal(SETCAPS_FUNC "failed: %s:"
                   " please ensure that the capset kernel"
                   " module is loaded.  see insmod(8)",
                   strbuf);
    }
}

#ifdef HAVE_LIBCAP
#define SET_CAP(flag) \
    do { \
        cap_flag_value_t curval; \
        capval = (flag); \
        err = cap_get_flag(curcaps, capval, CAP_PERMITTED, &curval); \
        if (err != -1 && curval) { \
            err = cap_set_flag(caps, CAP_EFFECTIVE, 1, &capval, CAP_SET); \
            if (err == -1) { \
                isc__strerror(errno, strbuf, sizeof(strbuf)); \
                ns_main_earlyfatal("cap_set_proc failed: %s", strbuf); \
            } \
            \
            err = cap_set_flag(caps, CAP_PERMITTED, 1, &capval, CAP_SET); \
            if (err == -1) { \
                isc__strerror(errno, strbuf, sizeof(strbuf)); \
                ns_main_earlyfatal("cap_set_proc failed: %s", strbuf); \
            } \
        } \
    } while (0)
#define INIT_CAP \
    do { \
        caps = cap_init(); \
        if (caps == NULL) { \
            isc__strerror(errno, strbuf, sizeof(strbuf)); \
            ns_main_earlyfatal("cap_init failed: %s", strbuf); \
        } \
        curcaps = cap_get_proc(); \
        if (curcaps == NULL) { \
            isc__strerror(errno, strbuf, sizeof(strbuf)); \
            ns_main_earlyfatal("cap_get_proc failed: %s", strbuf); \
        } \
    } while (0)
#define FREE_CAP \
    { \
        cap_free(caps); \
        cap_free(curcaps); \
    } while (0)
#else
#define SET_CAP(flag) do { caps |= (1 << (flag)); } while (0)
#define INIT_CAP do { caps = 0; } while (0)
#endif /* HAVE_LIBCAP */

static void
linux_initialprivs(void) {
    cap_t caps;
#ifdef HAVE_LIBCAP
    cap_t curcaps;
    cap_value_t capval;
    char strbuf[ISC_STRERRORSIZE];
    int err;
#endif

    /*%
     * We don't need most privileges, so we drop them right away.
     * Later on linux_minprivs() will be called, which will drop our
     * capabilities to the minimum needed to run the server.
     */
    INIT_CAP;

    /*
     * We need to be able to bind() to privileged ports, notably port 53!
     */
    SET_CAP(CAP_NET_BIND_SERVICE);

    /*
     * We need chroot() initially too.
     */
    SET_CAP(CAP_SYS_CHROOT);

#if defined(HAVE_SYS_PRCTL_H) || !defined(HAVE_LINUXTHREADS)
    /*
     * We can setuid() only if either the kernel supports keeping
     * capabilities after setuid() (which we don't know until we've
     * tried) or we're not using threads.  If either of these is
     * true, we want the setuid capability.
     */
    SET_CAP(CAP_SETUID);
#endif

    /*
     * Since we call initgroups, we need this.
     */
    SET_CAP(CAP_SETGID);

    /*
     * Without this, we run into problems reading a configuration file
     * owned by a non-root user and non-world-readable on startup.
     */
    SET_CAP(CAP_DAC_READ_SEARCH);

    /*
     * XXX  We might want to add CAP_SYS_RESOURCE, though it's not
     *      clear it would work right given the way linuxthreads work.
     * XXXDCL But since we need to be able to set the maximum number
     * of files, the stack size, data size, and core dump size to
     * support named.conf options, this is now being added to test.
     */
    SET_CAP(CAP_SYS_RESOURCE);

    /*
     * We need to be able to set the ownership of the containing
     * directory of the pid file when we create it.
     */
    SET_CAP(CAP_CHOWN);

    linux_setcaps(caps);

#ifdef HAVE_LIBCAP
    FREE_CAP;
#endif
}

static void
linux_minprivs(void) {
    cap_t caps;
#ifdef HAVE_LIBCAP
    cap_t curcaps;
    cap_value_t capval;
    char strbuf[ISC_STRERRORSIZE];
    int err;
#endif

    INIT_CAP;
    /*%
     * Drop all privileges except the ability to bind() to privileged
     * ports.
     *
     * It's important that we drop CAP_SYS_CHROOT.  If we didn't, it
     * chroot() could be used to escape from the chrooted area.
     */

    SET_CAP(CAP_NET_BIND_SERVICE);

    /*
     * XXX  We might want to add CAP_SYS_RESOURCE, though it's not
     *      clear it would work right given the way linuxthreads work.
     * XXXDCL But since we need to be able to set the maximum number
     * of files, the stack size, data size, and core dump size to
     * support named.conf options, this is now being added to test.
     */
    SET_CAP(CAP_SYS_RESOURCE);

    linux_setcaps(caps);

#ifdef HAVE_LIBCAP
    FREE_CAP;
#endif
}

#ifdef HAVE_SYS_PRCTL_H
static void
linux_keepcaps(void) {
    char strbuf[ISC_STRERRORSIZE];
    /*%
     * Ask the kernel to allow us to keep our capabilities after we
     * setuid().
     */

    if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0) {
        if (errno != EINVAL) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlyfatal("prctl() failed: %s", strbuf);
        }
    } else {
        non_root_caps = ISC_TRUE;
        if (getuid() != 0)
            non_root = ISC_TRUE;
    }
}
#endif

#endif  /* HAVE_LINUX_CAPABILITY_H */


static void
setup_syslog(const char *progname) {
    int options;

    options = LOG_PID;
#ifdef LOG_NDELAY
    options |= LOG_NDELAY;
#endif
    openlog(isc_file_basename(progname), options, ISC_FACILITY);
}

void
ns_os_init(const char *progname) {
    setup_syslog(progname);
#ifdef HAVE_LINUX_CAPABILITY_H
    linux_initialprivs();
#endif
#ifdef HAVE_LINUXTHREADS
    mainpid = getpid();
#endif
#ifdef SIGXFSZ
    signal(SIGXFSZ, SIG_IGN);
#endif
}

void
ns_os_daemonize(void) {
    pid_t pid;
    char strbuf[ISC_STRERRORSIZE];

    if (pipe(dfd) == -1) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("pipe(): %s", strbuf);
    }

    pid = fork();
    if (pid == -1) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("fork(): %s", strbuf);
    }
    if (pid != 0) {
        int n;
        /*
         * Wait for the child to finish loading for the first time.
         * This would be so much simpler if fork() worked once we
         * were multi-threaded.
         */
        (void)close(dfd[1]);
        do {
            char buf;
            n = read(dfd[0], &buf, 1);
            if (n == 1)
                _exit(0);
        } while (n == -1 && errno == EINTR);
        _exit(1);
    }
    (void)close(dfd[0]);

    /*
     * We're the child.
     */

#ifdef HAVE_LINUXTHREADS
    mainpid = getpid();
#endif

    if (setsid() == -1) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("setsid(): %s", strbuf);
    }

    /*
     * Try to set stdin, stdout, and stderr to /dev/null, but press
     * on even if it fails.
     *
     * XXXMLG The close() calls here are unneeded on all but NetBSD, but
     * are harmless to include everywhere.  dup2() is supposed to close
     * the FD if it is in use, but unproven-pthreads-0.16 is broken
     * and will end up closing the wrong FD.  This will be fixed eventually,
     * and these calls will be removed.
     */
    if (devnullfd != -1) {
        if (devnullfd != STDIN_FILENO) {
            (void)close(STDIN_FILENO);
            (void)dup2(devnullfd, STDIN_FILENO);
        }
        if (devnullfd != STDOUT_FILENO) {
            (void)close(STDOUT_FILENO);
            (void)dup2(devnullfd, STDOUT_FILENO);
        }
        if (devnullfd != STDERR_FILENO) {
            (void)close(STDERR_FILENO);
            (void)dup2(devnullfd, STDERR_FILENO);
        }
    }
}

void
ns_os_started(void) {
    char buf = 0;

    /*
     * Signal to the parent that we started successfully.
     */
    if (dfd[0] != -1 && dfd[1] != -1) {
        if (write(dfd[1], &buf, 1) != 1)
            ns_main_earlyfatal("unable to signal parent that we "
                       "otherwise started successfully.");
        close(dfd[1]);
        dfd[0] = dfd[1] = -1;
    }
}

void
ns_os_opendevnull(void) {
    devnullfd = open("/dev/null", O_RDWR, 0);
}

void
ns_os_closedevnull(void) {
    if (devnullfd != STDIN_FILENO &&
        devnullfd != STDOUT_FILENO &&
        devnullfd != STDERR_FILENO) {
        close(devnullfd);
        devnullfd = -1;
    }
}

static isc_boolean_t
all_digits(const char *s) {
    if (*s == '\0')
        return (ISC_FALSE);
    while (*s != '\0') {
        if (!isdigit((*s)&0xff))
            return (ISC_FALSE);
        s++;
    }
    return (ISC_TRUE);
}

void
ns_os_chroot(const char *root) {
    char strbuf[ISC_STRERRORSIZE];
#ifdef HAVE_LIBSCF
    ns_smf_chroot = 0;
#endif
    if (root != NULL) {
#ifdef HAVE_CHROOT
        if (chroot(root) < 0) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlyfatal("chroot(): %s", strbuf);
        }
#else
        ns_main_earlyfatal("chroot(): disabled");
#endif
        if (chdir("/") < 0) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlyfatal("chdir(/): %s", strbuf);
        }
#ifdef HAVE_LIBSCF
        /* Set ns_smf_chroot flag on successful chroot. */
        ns_smf_chroot = 1;
#endif
    }
}

void
ns_os_inituserinfo(const char *username) {
    char strbuf[ISC_STRERRORSIZE];
    if (username == NULL)
        return;

    if (all_digits(username))
        runas_pw = getpwuid((uid_t)atoi(username));
    else
        runas_pw = getpwnam(username);
    endpwent();

    if (runas_pw == NULL)
        ns_main_earlyfatal("user '%s' unknown", username);

    if (getuid() == 0) {
        if (initgroups(runas_pw->pw_name, runas_pw->pw_gid) < 0) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlyfatal("initgroups(): %s", strbuf);
        }
    }

}

void
ns_os_changeuser(void) {
    char strbuf[ISC_STRERRORSIZE];
    if (runas_pw == NULL || done_setuid)
        return;

    done_setuid = ISC_TRUE;

#ifdef HAVE_LINUXTHREADS
#ifdef HAVE_LINUX_CAPABILITY_H
    if (!non_root_caps)
        ns_main_earlyfatal("-u with Linux threads not supported: "
                   "requires kernel support for "
                   "prctl(PR_SET_KEEPCAPS)");
#else
    ns_main_earlyfatal("-u with Linux threads not supported: "
               "no capabilities support or capabilities "
               "disabled at build time");
#endif
#endif

    if (setgid(runas_pw->pw_gid) < 0) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("setgid(): %s", strbuf);
    }

    if (setuid(runas_pw->pw_uid) < 0) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("setuid(): %s", strbuf);
    }

#if defined(HAVE_SYS_PRCTL_H) && defined(PR_SET_DUMPABLE)
    /*
     * Restore the ability of named to drop core after the setuid()
     * call has disabled it.
     */
    if (prctl(PR_SET_DUMPABLE,1,0,0,0) < 0) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlywarning("prctl(PR_SET_DUMPABLE) failed: %s",
                     strbuf);
    }
#endif
#if defined(HAVE_LINUX_CAPABILITY_H) && !defined(HAVE_LINUXTHREADS)
    linux_minprivs();
#endif
}

void
ns_os_adjustnofile(void) {
#ifdef HAVE_LINUXTHREADS
    isc_result_t result;
    isc_resourcevalue_t newvalue;

    /*
     * Linux: max number of open files specified by one thread doesn't seem
     * to apply to other threads on Linux.
     */
    newvalue = ISC_RESOURCE_UNLIMITED;

    result = isc_resource_setlimit(isc_resource_openfiles, newvalue);
    if (result != ISC_R_SUCCESS)
        ns_main_earlywarning("couldn't adjust limit on open files");
#endif
}

void
ns_os_minprivs(void) {
#ifdef HAVE_SYS_PRCTL_H
    linux_keepcaps();
#endif

#ifdef HAVE_LINUXTHREADS
    ns_os_changeuser(); /* Call setuid() before threads are started */
#endif

#if defined(HAVE_LINUX_CAPABILITY_H) && defined(HAVE_LINUXTHREADS)
    linux_minprivs();
#endif
}

static int
safe_open(const char *filename, mode_t mode, isc_boolean_t append) {
    int fd;
    struct stat sb;

    if (stat(filename, &sb) == -1) {
        if (errno != ENOENT)
            return (-1);
    } else if ((sb.st_mode & S_IFREG) == 0) {
        errno = EOPNOTSUPP;
        return (-1);
    }

    if (append)
        fd = open(filename, O_WRONLY|O_CREAT|O_APPEND, mode);
    else {
        if (unlink(filename) < 0 && errno != ENOENT)
            return (-1);
        fd = open(filename, O_WRONLY|O_CREAT|O_EXCL, mode);
    }
    return (fd);
}

static void
cleanup_pidfile(void) {
    int n;
    if (pidfile != NULL) {
        n = unlink(pidfile);
        if (n == -1 && errno != ENOENT)
            ns_main_earlywarning("unlink '%s': failed", pidfile);
        free(pidfile);
    }
    pidfile = NULL;
}

static void
cleanup_lockfile(void) {
    if (singletonfd != -1) {
        close(singletonfd);
        singletonfd = -1;
    }

    if (lockfile != NULL) {
        int n = unlink(lockfile);
        if (n == -1 && errno != ENOENT)
            ns_main_earlywarning("unlink '%s': failed", lockfile);
        free(lockfile);
        lockfile = NULL;
    }
}

/*
 * Ensure that a directory exists.
 * NOTE: This function overwrites the '/' characters in 'filename' with
 * nulls. The caller should copy the filename to a fresh buffer first.
 */
static int
mkdirpath(char *filename, void (*report)(const char *, ...)) {
    char *slash = strrchr(filename, '/');
    char strbuf[ISC_STRERRORSIZE];
    unsigned int mode;

    if (slash != NULL && slash != filename) {
        struct stat sb;
        *slash = '\0';

        if (stat(filename, &sb) == -1) {
            if (errno != ENOENT) {
                isc__strerror(errno, strbuf, sizeof(strbuf));
                (*report)("couldn't stat '%s': %s", filename,
                      strbuf);
                goto error;
            }
            if (mkdirpath(filename, report) == -1)
                goto error;
            /*
             * Handle "//", "/./" and "/../" in path.
             */
            if (!strcmp(slash + 1, "") ||
                !strcmp(slash + 1, ".") ||
                !strcmp(slash + 1, "..")) {
                *slash = '/';
                return (0);
            }
            mode = S_IRUSR | S_IWUSR | S_IXUSR; /* u=rwx */
            mode |= S_IRGRP | S_IXGRP;      /* g=rx */
            mode |= S_IROTH | S_IXOTH;      /* o=rx */
            if (mkdir(filename, mode) == -1) {
                isc__strerror(errno, strbuf, sizeof(strbuf));
                (*report)("couldn't mkdir '%s': %s", filename,
                      strbuf);
                goto error;
            }
            if (runas_pw != NULL &&
                chown(filename, runas_pw->pw_uid,
                  runas_pw->pw_gid) == -1) {
                isc__strerror(errno, strbuf, sizeof(strbuf));
                (*report)("couldn't chown '%s': %s", filename,
                      strbuf);
            }
        }
        *slash = '/';
    }
    return (0);

 error:
    *slash = '/';
    return (-1);
}

static void
setperms(uid_t uid, gid_t gid) {
    char strbuf[ISC_STRERRORSIZE];
#if !defined(HAVE_SETEGID) && defined(HAVE_SETRESGID)
    gid_t oldgid, tmpg;
#endif
#if !defined(HAVE_SETEUID) && defined(HAVE_SETRESUID)
    uid_t olduid, tmpu;
#endif
#if defined(HAVE_SETEGID)
    if (getegid() != gid && setegid(gid) == -1) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlywarning("unable to set effective gid to %ld: %s",
                     (long)gid, strbuf);
    }
#elif defined(HAVE_SETRESGID)
    if (getresgid(&tmpg, &oldgid, &tmpg) == -1 || oldgid != gid) {
        if (setresgid(-1, gid, -1) == -1) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlywarning("unable to set effective "
                         "gid to %d: %s", gid, strbuf);
        }
    }
#endif

#if defined(HAVE_SETEUID)
    if (geteuid() != uid && seteuid(uid) == -1) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlywarning("unable to set effective uid to %ld: %s",
                     (long)uid, strbuf);
    }
#elif defined(HAVE_SETRESUID)
    if (getresuid(&tmpu, &olduid, &tmpu) == -1 || olduid != uid) {
        if (setresuid(-1, uid, -1) == -1) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlywarning("unable to set effective "
                         "uid to %d: %s", uid, strbuf);
        }
    }
#endif
}

FILE *
ns_os_openfile(const char *filename, mode_t mode, isc_boolean_t switch_user) {
    char strbuf[ISC_STRERRORSIZE], *f;
    FILE *fp;
    int fd;

    /*
     * Make the containing directory if it doesn't exist.
     */
    f = strdup(filename);
    if (f == NULL) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlywarning("couldn't strdup() '%s': %s",
                     filename, strbuf);
        return (NULL);
    }
    if (mkdirpath(f, ns_main_earlywarning) == -1) {
        free(f);
        return (NULL);
    }
    free(f);

    if (switch_user && runas_pw != NULL) {
#ifndef HAVE_LINUXTHREADS
        gid_t oldgid = getgid();
#endif
        /* Set UID/GID to the one we'll be running with eventually */
        setperms(runas_pw->pw_uid, runas_pw->pw_gid);

        fd = safe_open(filename, mode, ISC_FALSE);

#ifndef HAVE_LINUXTHREADS
        /* Restore UID/GID to root */
        setperms(0, oldgid);
#endif /* HAVE_LINUXTHREADS */

        if (fd == -1) {
#ifndef HAVE_LINUXTHREADS
            fd = safe_open(filename, mode, ISC_FALSE);
            if (fd != -1) {
                ns_main_earlywarning("Required root "
                             "permissions to open "
                             "'%s'.", filename);
            } else {
                ns_main_earlywarning("Could not open "
                             "'%s'.", filename);
            }
            ns_main_earlywarning("Please check file and "
                         "directory permissions "
                         "or reconfigure the filename.");
#else /* HAVE_LINUXTHREADS */
            ns_main_earlywarning("Could not open "
                         "'%s'.", filename);
            ns_main_earlywarning("Please check file and "
                         "directory permissions "
                         "or reconfigure the filename.");
#endif /* HAVE_LINUXTHREADS */
        }
    } else {
        fd = safe_open(filename, mode, ISC_FALSE);
    }

    if (fd < 0) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlywarning("could not open file '%s': %s",
                     filename, strbuf);
        return (NULL);
    }

    fp = fdopen(fd, "w");
    if (fp == NULL) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlywarning("could not fdopen() file '%s': %s",
                     filename, strbuf);
    }

    return (fp);
}

void
ns_os_writepidfile(const char *filename, isc_boolean_t first_time) {
    FILE *fh;
    pid_t pid;
    char strbuf[ISC_STRERRORSIZE];
    void (*report)(const char *, ...);

    /*
     * The caller must ensure any required synchronization.
     */

    report = first_time ? ns_main_earlyfatal : ns_main_earlywarning;

    cleanup_pidfile();

    if (filename == NULL)
        return;

    pidfile = strdup(filename);
    if (pidfile == NULL) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        (*report)("couldn't strdup() '%s': %s", filename, strbuf);
        return;
    }

    fh = ns_os_openfile(filename, S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH,
                  first_time);
    if (fh == NULL) {
        cleanup_pidfile();
        return;
    }
#ifdef HAVE_LINUXTHREADS
    pid = mainpid;
#else
    pid = getpid();
#endif
    if (fprintf(fh, "%ld\n", (long)pid) < 0) {
        (*report)("fprintf() to pid file '%s' failed", filename);
        (void)fclose(fh);
        cleanup_pidfile();
        return;
    }
    if (fflush(fh) == EOF) {
        (*report)("fflush() to pid file '%s' failed", filename);
        (void)fclose(fh);
        cleanup_pidfile();
        return;
    }
    (void)fclose(fh);
}

isc_boolean_t
ns_os_issingleton(const char *filename) {
    char strbuf[ISC_STRERRORSIZE];
    struct flock lock;

    if (singletonfd != -1)
        return (ISC_TRUE);

    if (strcasecmp(filename, "none") == 0)
        return (ISC_TRUE);

    /*
     * Make the containing directory if it doesn't exist.
     */
    lockfile = strdup(filename);
    if (lockfile == NULL) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("couldn't allocate memory for '%s': %s",
                   filename, strbuf);
    } else {
        int ret = mkdirpath(lockfile, ns_main_earlywarning);
        if (ret == -1) {
            ns_main_earlywarning("couldn't create '%s'", filename);
            cleanup_lockfile();
            return (ISC_FALSE);
        }
    }

    /*
     * ns_os_openfile() uses safeopen() which removes any existing
     * files. We can't use that here.
     */
    singletonfd = open(filename, O_WRONLY | O_CREAT,
               S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
    if (singletonfd == -1) {
        cleanup_lockfile();
        return (ISC_FALSE);
    }

    memset(&lock, 0, sizeof(lock));
    lock.l_type = F_WRLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = 0;
    lock.l_len = 1;

    /* Non-blocking (does not wait for lock) */
    if (fcntl(singletonfd, F_SETLK, &lock) == -1) {
        close(singletonfd);
        singletonfd = -1;
        return (ISC_FALSE);
    }

    return (ISC_TRUE);
}

void
ns_os_shutdown(void) {
    closelog();
    cleanup_pidfile();
    cleanup_lockfile();
}

isc_result_t
ns_os_gethostname(char *buf, size_t len) {
    int n;

    n = gethostname(buf, len);
    return ((n == 0) ? ISC_R_SUCCESS : ISC_R_FAILURE);
}

static char *
next_token(char **stringp, const char *delim) {
    char *res;

    do {
        res = strsep(stringp, delim);
        if (res == NULL)
            break;
    } while (*res == '\0');
    return (res);
}

void
ns_os_shutdownmsg(char *command, isc_buffer_t *text) {
    char *input, *ptr;
    unsigned int n;
    pid_t pid;

    input = command;

    /* Skip the command name. */
    ptr = next_token(&input, " \t");
    if (ptr == NULL)
        return;

    ptr = next_token(&input, " \t");
    if (ptr == NULL)
        return;

    if (strcmp(ptr, "-p") != 0)
        return;

#ifdef HAVE_LINUXTHREADS
    pid = mainpid;
#else
    pid = getpid();
#endif

    n = snprintf((char *)isc_buffer_used(text),
             isc_buffer_availablelength(text),
             "pid: %ld", (long)pid);
    /* Only send a message if it is complete. */
    if (n > 0 && n < isc_buffer_availablelength(text))
        isc_buffer_add(text, n);
}

void
ns_os_tzset(void) {
#ifdef HAVE_TZSET
    tzset();
#endif
}

static char unamebuf[BUFSIZ];
static char *unamep = NULL;

static void
getuname(void) {
#ifdef HAVE_UNAME
    struct utsname uts;

    memset(&uts, 0, sizeof(uts));
    if (uname(&uts) < 0) {
        strcpy(unamebuf, "unknown architecture");
        return;
    }

    snprintf(unamebuf, sizeof(unamebuf),
         "%s %s %s %s",
         uts.sysname, uts.machine, uts.release, uts.version);
#else
    strcpy(unamebuf, "unknown architecture");
#endif
    unamep = unamebuf;
}

char *
ns_os_uname(void) {
    if (unamep == NULL)
        getuname();
    return (unamep);
}