named/unix/os.c

	os.c revision 764808211e952f1617aaa609281da66d80120c0d
/*
 * Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC")
 * Copyright (C) 1999-2002  Internet Software Consortium.
 *
 * 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 ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC 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.
 */

/* $Id: os.c,v 1.67 2004/04/15 04:49:50 marka Exp $ */

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

#include <sys/types.h>  /* dev_t FreeBSD 2.1 */
#include <sys/stat.h>

#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/result.h>
#include <isc/strerror.h>
#include <isc/string.h>

#include <named/main.h>
#include <named/os.h>

static char *pidfile = NULL;
static int devnullfd = -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_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;

#ifdef HAVE_LINUX_CAPABILITY_H

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

/*
 * 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 <sys/syscall.h>    /* Required for syscall(). */
#include <linux/capability.h>   /* Required for _LINUX_CAPABILITY_VERSION. */

#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 */

#ifndef SYS_capset
#ifndef __NR_capset
#include <asm/unistd.h> /* Slackware 4.0 needs this. */
#endif
#define SYS_capset __NR_capset
#endif

static void
linux_setcaps(unsigned int caps) {
    struct __user_cap_header_struct caphead;
    struct __user_cap_data_struct cap;
    char strbuf[ISC_STRERRORSIZE];

    if ((getuid() != 0 && !non_root_caps) || non_root)
        return;

    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 = caps;
    if (syscall(SYS_capset, &caphead, &cap) < 0) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("capset failed: %s", strbuf);
    }
}

static void
linux_initialprivs(void) {
    unsigned int caps;

    /*
     * 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.
     */

    caps = 0;

    /*
     * We need to be able to bind() to privileged ports, notably port 53!
     */
    caps |= (1 << CAP_NET_BIND_SERVICE);

    /*
     * We need chroot() initially too.
     */
    caps |= (1 << 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.
     */
    caps |= (1 << CAP_SETUID);
#endif

    /*
     * Since we call initgroups, we need this.
     */
    caps |= (1 << CAP_SETGID);

    /*
     * Without this, we run into problems reading a configuration file
     * owned by a non-root user and non-world-readable on startup.
     */
    caps |= (1 << 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.
     */
    caps |= (1 << CAP_SYS_RESOURCE);

    linux_setcaps(caps);
}

static void
linux_minprivs(void) {
    unsigned int caps;

    /*
     * 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.
     */

    caps = 0;
    caps |= (1 << 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.
     */
    caps |= (1 << CAP_SYS_RESOURCE);

    linux_setcaps(caps);
}

#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];

    pid = fork();
    if (pid == -1) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        ns_main_earlyfatal("fork(): %s", strbuf);
    }
    if (pid != 0)
        _exit(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_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];
    if (root != NULL) {
        if (chroot(root) < 0) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlyfatal("chroot(): %s", strbuf);
        }
        if (chdir("/") < 0) {
            isc__strerror(errno, strbuf, sizeof(strbuf));
            ns_main_earlyfatal("chdir(/): %s", strbuf);
        }
    }
}

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)
#endif
        ns_main_earlyfatal(
           "-u not supported on Linux kernels older than "
           "2.3.99-pre3 or 2.2.18 when using threads");
#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_LINUX_CAPABILITY_H) && !defined(HAVE_LINUXTHREADS)
    linux_minprivs();
#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, 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,
              S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
    else {
        (void)unlink(filename);
        fd = open(filename, O_WRONLY|O_CREAT|O_EXCL,
              S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
    }
    return (fd);
}

static void
cleanup_pidfile(void) {
    if (pidfile != NULL) {
        (void)unlink(pidfile);
        free(pidfile);
    }
    pidfile = NULL;
}

void
ns_os_writepidfile(const char *filename, isc_boolean_t first_time) {
    int fd;
    FILE *lockfile;
    size_t len;
    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;

    len = strlen(filename);
    pidfile = malloc(len + 1);
    if (pidfile == NULL) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        (*report)("couldn't malloc '%s': %s", filename, strbuf);
        return;
    }
    /* This is safe. */
    strcpy(pidfile, filename);

    fd = safe_open(filename, ISC_FALSE);
    if (fd < 0) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        (*report)("couldn't open pid file '%s': %s", filename, strbuf);
        free(pidfile);
        pidfile = NULL;
        return;
    }
    lockfile = fdopen(fd, "w");
    if (lockfile == NULL) {
        isc__strerror(errno, strbuf, sizeof(strbuf));
        (*report)("could not fdopen() pid file '%s': %s",
              filename, strbuf);
        (void)close(fd);
        cleanup_pidfile();
        return;
    }
#ifdef HAVE_LINUXTHREADS
    pid = mainpid;
#else
    pid = getpid();
#endif
    if (fprintf(lockfile, "%ld\n", (long)pid) < 0) {
        (*report)("fprintf() to pid file '%s' failed", filename);
        (void)fclose(lockfile);
        cleanup_pidfile();
        return;
    }
    if (fflush(lockfile) == EOF) {
        (*report)("fflush() to pid file '%s' failed", filename);
        (void)fclose(lockfile);
        cleanup_pidfile();
        return;
    }
    (void)fclose(lockfile);
}

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

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: %d", pid);
    /* Only send a message if it is complete. */
    if (n < isc_buffer_availablelength(text))
        isc_buffer_add(text, n);
}

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