source: trunk/minix/commands/i386/mtools-3.9.7/privileges.c@ 11

#include "sysincludes.h"
#include "msdos.h"
#include "mtools.h"

/*#define PRIV_DEBUG*/

#if 0
#undef HAVE_SETEUID
#define HAVE_SETRESUID
#include <asm/unistd.h>
int setresuid(int a, int b, int c)
{
        syscall(164, a, b, c);

}
#endif

static inline void print_privs(const char *message)
{
#ifdef PRIV_DEBUG
        /* for debugging purposes only */
        fprintf(stderr,"%s egid=%d rgid=%d\n", message, getegid(), getgid());
        fprintf(stderr,"%s euid=%d ruid=%d\n", message, geteuid(), getuid());
#endif
}

int noPrivileges=0;


static gid_t rgid, egid;
static uid_t ruid, euid;

/* privilege management routines for SunOS and Solaris.  These are
 * needed in order to issue raw SCSI read/write ioctls.  Mtools drops
 * its privileges at the beginning, and reclaims them just for the
 * above-mentioned ioctl's.  Before popen(), exec() or system, it
 * drops its privileges completely, and issues a warning.
 */


/* group id handling is lots easyer, as long as we don't use group 0.
 * If you want to use group id's, create a *new* group mtools or
 * floppy.  Chgrp any devices that you only want to be accessible to
 * mtools to this group, and give them the appropriate privs.  Make
 * sure this group doesn't own any other files: be aware that any user
 * with access to mtools may mformat these files!
 */


static inline void Setuid(uid_t uid)
{
#if defined HAVE_SETEUID || defined HAVE_SETRESUID
        if(euid == 0) {
#ifdef HAVE_SETEUID
                seteuid(uid);
#else
                setresuid(ruid, uid, euid);
#endif
        } else
#endif
                setuid(uid);
}

/* In reclaim_privs and drop privs, we have to manipulate group privileges
 * when having no root privileges, else we might lose them */

void reclaim_privs(void)
{
        if(noPrivileges)
                return;
        setgid(egid);
        Setuid(euid);
        print_privs("after reclaim privs, both uids should be 0 ");
}

void drop_privs(void)
{
        Setuid(ruid);
        setgid(rgid);
        print_privs("after drop_privs, real should be 0, effective should not ");
}

void destroy_privs(void)
{

#if defined HAVE_SETEUID || defined HAVE_SETRESUID
        if(euid == 0) {
#ifdef HAVE_SETEUID
                setuid(0); /* get the necessary privs to drop real root id */
                setuid(ruid); /* this should be enough to get rid of the three
                               * ids */
                seteuid(ruid); /* for good measure... just in case we came
                                * accross a system which implemented sane
                                * semantics instead of POSIXly broken
                                * semantics for setuid */
#else
                setresuid(ruid, ruid, ruid);
#endif
        }
#endif

        /* we also destroy group privileges */
        drop_privs();

        /* saved set [ug]id will go away by itself on exec */

        print_privs("destroy_privs, no uid should be zero  ");
}


uid_t get_real_uid(void)
{
        return ruid;
}

void init_privs(void)
{
        euid = geteuid();
        ruid = getuid();
        egid = getegid();
        rgid = getgid();

#ifndef F_SETFD
        if(euid != ruid) {
                fprintf(stderr,
                        "Setuid installation not supported on this platform\n");
                fprintf(stderr,
                        "Missing F_SETFD");
                exit(1);
        }
#endif
        
        if(euid == 0 && ruid != 0) {
#ifdef HAVE_SETEUID
                setuid(0); /* set real uid to 0 */
#else
#ifndef HAVE_SETRESUID
                /* on this machine, it is not possible to reversibly drop
                 * root privileges.  We print an error and quit */

                /* BEOS is no longer a special case, as both euid and ruid
                 * return 0, and thus we do not get any longer into this
                 * branch */
                fprintf(stderr,
                        "Seteuid call not supported on this architecture.\n");
                fprintf(stderr,
                        "Mtools cannot be installed setuid root.\n");
                fprintf(stderr,
                        "However, it can be installed setuid to a non root");
                fprintf(stderr,
                        "user or setgid to any id.\n");
                exit(1);
#endif
#endif
        }
        
        drop_privs();
        print_privs("after init, real should be 0, effective should not ");
}

void closeExec(int fd)
{
#ifdef F_SETFD
        fcntl(fd, F_SETFD, 1);
#endif
}