smbumount.c

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/*
 *  smbumount.c
 *
 *  Copyright (C) 1995-1998 by Volker Lendecke
 *
 */

#include "includes.h"

#include <mntent.h>

#include <asm/types.h>
#include <asm/posix_types.h>
#include <linux/smb.h>
#include <linux/smb_mount.h>
#include <linux/smb_fs.h>

/* This is a (hopefully) temporary hack due to the fact that
	sizeof( uid_t ) != sizeof( __kernel_uid_t ) under glibc.
	This may change in the future and smb.h may get fixed in the
	future.  In the mean time, it's ugly hack time - get over it.
*/
#undef SMB_IOC_GETMOUNTUID
#define	SMB_IOC_GETMOUNTUID		_IOR('u', 1, __kernel_uid_t)

#ifndef O_NOFOLLOW
#define O_NOFOLLOW     0400000
#endif

static void
usage(void)
{
        printf("usage: smbumount mountpoint\n");
}

static int
umount_ok(const char *mount_point)
{
	/* we set O_NOFOLLOW to prevent users playing games with symlinks to
	   umount filesystems they don't own */
        int fid = open(mount_point, O_RDONLY|O_NOFOLLOW, 0);
        __kernel_uid_t mount_uid;
	
        if (fid == -1) {
                fprintf(stderr, "Could not open %s: %s\n",
                        mount_point, strerror(errno));
                return -1;
        }
        
        if (ioctl(fid, SMB_IOC_GETMOUNTUID, &mount_uid) != 0) {
                fprintf(stderr, "%s probably not smb-filesystem\n",
                        mount_point);
                return -1;
        }

        if ((getuid() != 0)
            && (mount_uid != getuid())) {
                fprintf(stderr, "You are not allowed to umount %s\n",
                        mount_point);
                return -1;
        }

        close(fid);
        return 0;
}

/* Make a canonical pathname from PATH.  Returns a freshly malloced string.
   It is up the *caller* to ensure that the PATH is sensible.  i.e.
   canonicalize ("/dev/fd0/.") returns "/dev/fd0" even though ``/dev/fd0/.''
   is not a legal pathname for ``/dev/fd0''  Anything we cannot parse
   we return unmodified.   */
static char *
canonicalize (char *path)
{
	char *canonical = malloc (PATH_MAX + 1);

	if (!canonical) {
		fprintf(stderr, "Error! Not enough memory!\n");
		return NULL;
	}

	if (strlen(path) > PATH_MAX) {
		fprintf(stderr, "Mount point string too long\n");
		return NULL;
	}

	if (path == NULL)
		return NULL;
  
	if (realpath (path, canonical))
		return canonical;

	strncpy (canonical, path, PATH_MAX);
	canonical[PATH_MAX] = '\0';
	return canonical;
}


int 
main(int argc, char *argv[])
{
        int fd;
        char* mount_point;
        struct mntent *mnt;
        FILE* mtab;
        FILE* new_mtab;

        if (argc != 2) {
                usage();
                exit(1);
        }

        if (geteuid() != 0) {
                fprintf(stderr, "smbumount must be installed suid root\n");
                exit(1);
        }

        mount_point = canonicalize(argv[1]);

	if (mount_point == NULL)
	{
		exit(1);
	}

        if (umount_ok(mount_point) != 0) {
                exit(1);
        }

        if (umount(mount_point) != 0) {
                fprintf(stderr, "Could not umount %s: %s\n",
                        mount_point, strerror(errno));
                exit(1);
        }

        if ((fd = open(MOUNTED"~", O_RDWR|O_CREAT|O_EXCL, 0600)) == -1)
        {
                fprintf(stderr, "Can't get "MOUNTED"~ lock file");
                return 1;
        }
        close(fd);
	
        if ((mtab = setmntent(MOUNTED, "r")) == NULL) {
                fprintf(stderr, "Can't open " MOUNTED ": %s\n",
                        strerror(errno));
                return 1;
        }

#define MOUNTED_TMP MOUNTED".tmp"

        if ((new_mtab = setmntent(MOUNTED_TMP, "w")) == NULL) {
                fprintf(stderr, "Can't open " MOUNTED_TMP ": %s\n",
                        strerror(errno));
                endmntent(mtab);
                return 1;
        }

        while ((mnt = getmntent(mtab)) != NULL) {
                if (strcmp(mnt->mnt_dir, mount_point) != 0) {
                        addmntent(new_mtab, mnt);
                }
        }

        endmntent(mtab);

        if (fchmod (fileno (new_mtab), S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH) < 0) {
                fprintf(stderr, "Error changing mode of %s: %s\n",
                        MOUNTED_TMP, strerror(errno));
                exit(1);
        }

        endmntent(new_mtab);

        if (rename(MOUNTED_TMP, MOUNTED) < 0) {
                fprintf(stderr, "Cannot rename %s to %s: %s\n",
                        MOUNTED, MOUNTED_TMP, strerror(errno));
                exit(1);
        }

        if (unlink(MOUNTED"~") == -1)
        {
                fprintf(stderr, "Can't remove "MOUNTED"~");
                return 1;
        }

	return 0;
}