setuid.c

刻录光盘的程序

/* @(#)setuid.c	1.2 99/12/19 Copyright 1998,1999 Heiko Eissfeldt */
#ifndef lint
static char     sccsid[] =
"@(#)setuid.c	1.2 99/12/19 Copyright 1998,1999 Heiko Eissfeldt";

#endif
/* Security functions by zblaxell

   If these functions fail, it is because there was an installation error
   or a programming error, and we can't be sure about what privileges
   we do or do not have.  This means we might not be able to recover
   the privileges we need to fix anything that may be broken (e.g. the
   CDDA state of some interface types), and we may in fact do something
   quite dangerous (like write to the WAV file as root).

   In any case, it is unsafe to do anything but exit *now*.  Ideally we'd
   kill -9 our process group too, just to be sure.  Root privileges are not
   something you want floating around at random in user-level applications.

   If any signal handlers or child processes are introduced into this
   program, it will be necessary to call dontneedroot() or neverneedroot()
   on entry, respectively; otherwise, it will be possible to trick
   the program into executing the signal handler or child process with
   root privileges by sending signals at the right time.
 */

#include "config.h"
#if defined (HAVE_UNISTD_H) && (HAVE_UNISTD_H == 1)
#include <sys/types.h>
#include <unistd.h>
#endif
#include <stdio.h>
#include <stdlib.h>

#include "setuid.h"

#undef DEBUG

/* True at return from initsecurity */
static uid_t real_uid = (uid_t) (-1);
static uid_t effective_uid = (uid_t) (-1);
static gid_t real_gid = (gid_t) (-1);
static gid_t effective_gid = (gid_t) (-1);

/* Run this at the beginning of the program to initialize this code and
   to drop privileges before someone uses them to shoot us in the foot.
   Do not pass(go), do not dollars += 200. */

void initsecurity()
{
    int leffective_uid;

    alarm(0);			/* can be inherited from parent process */
    real_uid = getuid();
    leffective_uid = geteuid();
    if ((int) real_uid != leffective_uid && leffective_uid != 0) { /* sanity check */
        fprintf(stderr, "Warning: setuid but not to root (uid=%ld, euid=%d)\n", (long) real_uid, leffective_uid);
        fprintf(stderr, "Dropping setuid privileges now.\n");
        neverneedroot();
    } else {
        effective_uid = leffective_uid;
    }
    real_gid = getgid();
    effective_gid = getegid();
    dontneedroot();
    dontneedgroup();
}

/* Temporarily gain root privileges. */

#if defined _POSIX_SAVED_IDS && defined (HAVE_SETEUID) && defined SCO
/* SCO seems to lack the prototypes... */
int	seteuid __PR((uid_t euid));
int	setegid __PR((gid_t guid));
#endif

void needroot(necessary)
	int necessary;
{
#ifdef DEBUG
    fprintf(stderr, "call to     needroot (_euid_=%d, uid=%d), current=%d\n",effective_uid, real_uid, geteuid());
#endif
    if (effective_uid) {
        if (necessary) {
	  fprintf(stderr, "Fatal error:  require root privilege but not setuid root.\n");
	  exit(1);
	} else
	  return;
    }
    if (real_uid == (uid_t) (-1)) {
	fprintf(stderr, "Fatal error:  initsecurity() not called.\n");
	exit(1);
    }
    if (geteuid() == 0) return; /* nothing to do */

#if defined _POSIX_SAVED_IDS && defined (HAVE_SETEUID)
    if (seteuid(effective_uid)) {
	perror("seteuid in needroot()");
	exit(1);
    }
#else
#if defined (HAVE_SETREUID)
    if (setreuid(real_uid, effective_uid)) {
	perror("setreuid in needroot()");
	exit(1);
    }
#endif
#endif
    if (geteuid() != 0 && necessary) {
	fprintf(stderr, "Fatal error:  did not get root privilege.\n");
	exit(1);
    }
}

/* Temporarily drop root privileges.  */

void dontneedroot()
{
#ifdef DEBUG
    fprintf(stderr, "call to dontneedroot (euid=%d, _uid_=%d), current=%d\n",effective_uid, real_uid, geteuid());
#endif
    if (effective_uid)
	return;
    if (real_uid == (uid_t) (-1)) {
	fprintf(stderr, "Fatal error:  initsecurity() not called.\n");
	exit(1);
    }
    if (geteuid() != 0) return; /* nothing to do */

#if defined _POSIX_SAVED_IDS && defined (HAVE_SETEUID)
    if (seteuid(real_uid)) {
	perror("seteuid in dontneedroot()");
	exit(1);
    }
#else
#if defined (HAVE_SETREUID)
    if (setreuid(effective_uid, real_uid)) {
	perror("setreuid in dontneedroot()");
	exit(1);
    }
#endif
#endif
    if (geteuid() != real_uid) {
	fprintf(stderr, "Fatal error:  did not drop root privilege.\n");
	exit(1);
    }
}

/* Permanently drop root privileges.  */

void neverneedroot()
{
#ifdef DEBUG
    fprintf(stderr, "call to neverneedroot (euid=%d, uid=%d)\n",effective_uid, real_uid);
#endif
    if (real_uid == (uid_t) (-1)) {
	fprintf(stderr, "Fatal error:  initsecurity() not called.\n");
	exit(1);
    }
    if (geteuid() == 0) {
#if defined (HAVE_SETUID)
      if (setuid(real_uid)) {
	  perror("setuid in neverneedroot()");
	  exit(1);
      }
#endif
    }
    if (geteuid() != real_uid || getuid() != real_uid) {
	fprintf(stderr, "Fatal error:  did not drop root privilege.\n");
	exit(1);
    }
    effective_uid = real_uid;
}

/* Temporarily gain group privileges. */

void needgroup(necessary)
	int necessary;
{
#ifdef DEBUG
    fprintf(stderr, "call to needgroup (egid=%d, gid=%d)\n",effective_gid, real_gid);
#endif
    if (real_gid == (gid_t) (-1)) {
	fprintf(stderr, "Fatal error:  initsecurity() not called.\n");
	exit(1);
    }

    if (getegid() == effective_gid) return; /* nothing to do */

#if defined _POSIX_SAVED_IDS && defined (HAVE_SETEGID)
    if (setegid(effective_gid)) {
	perror("setegid in needgroup()");
	exit(1);
    }
#else
#if defined (HAVE_SETREGID)
    if (setregid(real_gid, effective_gid)) {
	perror("setregid in needgroup()");
	exit(1);
    }
#endif
#endif
    if (necessary && getegid() != effective_gid) {
	fprintf(stderr, "Fatal error:  did not get group privilege.\n");
	exit(1);
    }
}

/* Temporarily drop group privileges.  */

void dontneedgroup()
{
#ifdef DEBUG
    fprintf(stderr, "call to dontneedgroup (egid=%d, gid=%d)\n",effective_gid, real_gid);
#endif
    if (real_gid == (gid_t) (-1)) {
	fprintf(stderr, "Fatal error:  initsecurity() not called.\n");
	exit(1);
    }
    if (getegid() != effective_gid) return; /* nothing to do */
#if defined _POSIX_SAVED_IDS && defined (HAVE_SETEGID)
    if (setegid(real_gid)) {
	perror("setegid in dontneedgroup()");
	exit(1);
    }
#else
#if defined (HAVE_SETREGID)
    if (setregid(effective_gid, real_gid)) {
	perror("setregid in dontneedgroup()");
	exit(1);
    }
#endif
#endif
    if (getegid() != real_gid) {
	fprintf(stderr, "Fatal error:  did not drop group privilege.\n");
	exit(1);
    }
}

/* Permanently drop group privileges.  */

void neverneedgroup()
{
#ifdef DEBUG
    fprintf(stderr, "call to neverneedgroup (egid=%d, gid=%d)\n",effective_gid, real_gid);
#endif
    if (real_gid == (gid_t) (-1)) {
	fprintf(stderr, "Fatal error:  initsecurity() not called.\n");
	exit(1);
    }
    if (getegid() != effective_gid) {
#if defined (HAVE_SETUID)
      if (setgid(real_gid)) {
	  perror("setgid in neverneedgroup()");
	  exit(1);
      }
#endif
    }
    if (getegid() != real_gid || getgid() != real_gid) {
	fprintf(stderr, "Fatal error:  did not drop group privilege.\n");
	exit(1);
    }
    effective_gid = real_gid;
}

#if defined (HPUX)
int seteuid(uid)
	uid_t uid;
{
  return setresuid(-1, uid, -1);
}

int setreuid(uid1, uid2)
	uid_t uid1;
	uid_t uid2;
{
  return setresuid(uid2, uid2, uid1 == uid2 ? uid2 : 0);
}

int setregid(gid1, gid2)
	gid_t gid1;
	gid_t gid2;
{
  return setresgid(gid2, gid2, gid1 == gid2 ? gid2 : 0);
}
#endif