root/linux/syslinux.c

/* ----------------------------------------------------------------------- *
 *
 *   Copyright 1998-2008 H. Peter Anvin - All Rights Reserved
 *   Copyright 2009-2010 Intel Corporation; author: H. Peter Anvin
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
 *   Boston MA 02111-1307, USA; either version 2 of the License, or
 *   (at your option) any later version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * syslinux.c - Linux installer program for SYSLINUX
 *
 * This is Linux-specific by now.
 *
 * This is an alternate version of the installer which doesn't require
 * mtools, but requires root privilege.
 */

/*
 * If DO_DIRECT_MOUNT is 0, call mount(8)
 * If DO_DIRECT_MOUNT is 1, call mount(2)
 */
#ifdef __KLIBC__
# define DO_DIRECT_MOUNT 1
#else
# define DO_DIRECT_MOUNT 0      /* glibc has broken losetup ioctls */
#endif

#define _GNU_SOURCE
#define _XOPEN_SOURCE 500       /* For pread() pwrite() */
#define _FILE_OFFSET_BITS 64
#include <alloca.h>
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <inttypes.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mount.h>

#include "linuxioctl.h"

#include <paths.h>
#ifndef _PATH_MOUNT
# define _PATH_MOUNT "/bin/mount"
#endif
#ifndef _PATH_UMOUNT
# define _PATH_UMOUNT "/bin/umount"
#endif
#ifndef _PATH_TMP
# define _PATH_TMP "/tmp/"
#endif

#include "syslinux.h"

#if DO_DIRECT_MOUNT
# include <linux/loop.h>
#endif

#include <getopt.h>
#include <sysexits.h>
#include "syslxcom.h"
#include "syslxfs.h"
#include "setadv.h"
#include "syslxopt.h" /* unified options */

extern const char *program;     /* Name of program */

pid_t mypid;
char *mntpath = NULL;           /* Path on which to mount */

#if DO_DIRECT_MOUNT
int loop_fd = -1;               /* Loop device */
#endif

void __attribute__ ((noreturn)) die(const char *msg)
{
    fprintf(stderr, "%s: %s\n", program, msg);

#if DO_DIRECT_MOUNT
    if (loop_fd != -1) {
        ioctl(loop_fd, LOOP_CLR_FD, 0); /* Free loop device */
        close(loop_fd);
        loop_fd = -1;
    }
#endif

    if (mntpath)
        unlink(mntpath);

    exit(1);
}

/*
 * Mount routine
 */
int do_mount(int dev_fd, int *cookie, const char *mntpath, const char *fstype)
{
    struct stat st;

    (void)cookie;

    if (fstat(dev_fd, &st) < 0)
        return errno;

#if DO_DIRECT_MOUNT
    {
        if (!S_ISBLK(st.st_mode)) {
            /* It's file, need to mount it loopback */
            unsigned int n = 0;
            struct loop_info64 loopinfo;
            int loop_fd;

            for (n = 0; loop_fd < 0; n++) {
                snprintf(devfdname, sizeof devfdname, "/dev/loop%u", n);
                loop_fd = open(devfdname, O_RDWR);
                if (loop_fd < 0 && errno == ENOENT) {
                    die("no available loopback device!");
                }
                if (ioctl(loop_fd, LOOP_SET_FD, (void *)dev_fd)) {
                    close(loop_fd);
                    loop_fd = -1;
                    if (errno != EBUSY)
                        die("cannot set up loopback device");
                    else
                        continue;
                }

                if (ioctl(loop_fd, LOOP_GET_STATUS64, &loopinfo) ||
                    (loopinfo.lo_offset = opt.offset,
                     ioctl(loop_fd, LOOP_SET_STATUS64, &loopinfo)))
                    die("cannot set up loopback device");
            }

            *cookie = loop_fd;
        } else {
            snprintf(devfdname, sizeof devfdname, "/proc/%lu/fd/%d",
                     (unsigned long)mypid, dev_fd);
            *cookie = -1;
        }

        return mount(devfdname, mntpath, fstype,
                     MS_NOEXEC | MS_NOSUID, "umask=077,quiet");
    }
#else
    {
        char devfdname[128], mnt_opts[128];
        pid_t f, w;
        int status;

        snprintf(devfdname, sizeof devfdname, "/proc/%lu/fd/%d",
                 (unsigned long)mypid, dev_fd);

        f = fork();
        if (f < 0) {
            return -1;
        } else if (f == 0) {
            if (!S_ISBLK(st.st_mode)) {
                snprintf(mnt_opts, sizeof mnt_opts,
                         "rw,nodev,noexec,loop,offset=%llu,umask=077,quiet",
                         (unsigned long long)opt.offset);
            } else {
                snprintf(mnt_opts, sizeof mnt_opts,
                         "rw,nodev,noexec,umask=077,quiet");
            }
            execl(_PATH_MOUNT, _PATH_MOUNT, "-t", fstype, "-o", mnt_opts,
                  devfdname, mntpath, NULL);
            _exit(255);         /* execl failed */
        }

        w = waitpid(f, &status, 0);
        return (w != f || status) ? -1 : 0;
    }
#endif
}

/*
 * umount routine
 */
void do_umount(const char *mntpath, int cookie)
{
#if DO_DIRECT_MOUNT
    int loop_fd = cookie;

    if (umount2(mntpath, 0))
        die("could not umount path");

    if (loop_fd != -1) {
        ioctl(loop_fd, LOOP_CLR_FD, 0); /* Free loop device */
        close(loop_fd);
        loop_fd = -1;
    }
#else
    pid_t f = fork();
    pid_t w;
    int status;
    (void)cookie;

    if (f < 0) {
        perror("fork");
        exit(1);
    } else if (f == 0) {
        execl(_PATH_UMOUNT, _PATH_UMOUNT, mntpath, NULL);
    }

    w = waitpid(f, &status, 0);
    if (w != f || status) {
        exit(1);
    }
#endif
}

/*
 * Modify the ADV of an existing installation
 */
int modify_existing_adv(const char *path)
{
    if (opt.reset_adv)
        syslinux_reset_adv(syslinux_adv);
    else if (read_adv(path, "ldlinux.sys") < 0)
        return 1;

    if (modify_adv() < 0)
        return 1;

    if (write_adv(path, "ldlinux.sys") < 0)
        return 1;

    return 0;
}

int main(int argc, char *argv[])
{
    static unsigned char sectbuf[SECTOR_SIZE];
    int dev_fd, fd;
    struct stat st;
    int err = 0;
    char mntname[128];
    char *ldlinux_name;
    char *ldlinux_path;
    char *subdir;
    sector_t *sectors = NULL;
    int ldlinux_sectors = (boot_image_len + SECTOR_SIZE - 1) >> SECTOR_SHIFT;
    const char *errmsg;
    int mnt_cookie;
    int patch_sectors;
    int i;

    mypid = getpid();
    umask(077);
    parse_options(argc, argv, MODE_SYSLINUX);

    /* Note: subdir is guaranteed to start and end in / */
    if (opt.directory && opt.directory[0]) {
        int len = strlen(opt.directory);
        int rv = asprintf(&subdir, "%s%s%s",
                          opt.directory[0] == '/' ? "" : "/",
                          opt.directory,
                          opt.directory[len-1] == '/' ? "" : "/");
        if (rv < 0 || !subdir) {
            perror(program);
            exit(1);
        }
    } else {
        subdir = "/";
    }

    if (!opt.device || opt.install_mbr || opt.activate_partition)
        usage(EX_USAGE, MODE_SYSLINUX);

    /*
     * First make sure we can open the device at all, and that we have
     * read/write permission.
     */
    dev_fd = open(opt.device, O_RDWR);
    if (dev_fd < 0 || fstat(dev_fd, &st) < 0) {
        perror(opt.device);
        exit(1);
    }

    if (!S_ISBLK(st.st_mode) && !S_ISREG(st.st_mode) && !S_ISCHR(st.st_mode)) {
        die("not a device or regular file");
    }

    if (opt.offset && S_ISBLK(st.st_mode)) {
        die("can't combine an offset with a block device");
    }

    xpread(dev_fd, sectbuf, SECTOR_SIZE, opt.offset);
    fsync(dev_fd);

    /*
     * Check to see that what we got was indeed an FAT/NTFS
     * boot sector/superblock
     */
    if ((errmsg = syslinux_check_bootsect(sectbuf, &fs_type))) {
        fprintf(stderr, "%s: %s\n", opt.device, errmsg);
        exit(1);
    }

    /*
     * Now mount the device.
     */
    if (geteuid()) {
        die("This program needs root privilege");
    } else {
        int i = 0;
        struct stat dst;
        int rv;

        /* We're root or at least setuid.
           Make a temp dir and pass all the gunky options to mount. */

        if (chdir(_PATH_TMP)) {
            fprintf(stderr, "%s: Cannot access the %s directory.\n",
                    program, _PATH_TMP);
            exit(1);
        }
#define TMP_MODE (S_IXUSR|S_IWUSR|S_IXGRP|S_IWGRP|S_IWOTH|S_IXOTH|S_ISVTX)

        if (stat(".", &dst) || !S_ISDIR(dst.st_mode) ||
            (dst.st_mode & TMP_MODE) != TMP_MODE) {
            die("possibly unsafe " _PATH_TMP " permissions");
        }

        for (i = 0;; i++) {
            snprintf(mntname, sizeof mntname, "syslinux.mnt.%lu.%d",
                     (unsigned long)mypid, i);

            if (lstat(mntname, &dst) != -1 || errno != ENOENT)
                continue;

            rv = mkdir(mntname, 0000);

            if (rv == -1) {
                if (errno == EEXIST || errno == EINTR)
                    continue;
                perror(program);
                exit(1);
            }

            if (lstat(mntname, &dst) || dst.st_mode != (S_IFDIR | 0000) ||
                dst.st_uid != 0) {
                die("someone is trying to symlink race us!");
            }
            break;              /* OK, got something... */
        }

        mntpath = mntname;
    }

    if (fs_type == VFAT) {
        if (do_mount(dev_fd, &mnt_cookie, mntpath, "vfat") &&
            do_mount(dev_fd, &mnt_cookie, mntpath, "msdos")) {
            rmdir(mntpath);
            die("failed on mounting fat volume");
        }
    } else if (fs_type == NTFS) {
        if (do_mount(dev_fd, &mnt_cookie, mntpath, "ntfs-3g")) {
            rmdir(mntpath);
            die("failed on mounting ntfs volume");
        }
    }

    ldlinux_path = alloca(strlen(mntpath) + strlen(subdir) + 1);
    sprintf(ldlinux_path, "%s%s", mntpath, subdir);

    ldlinux_name = alloca(strlen(ldlinux_path) + 14);
    if (!ldlinux_name) {
        perror(program);
        err = 1;
        goto umount;
    }
    sprintf(ldlinux_name, "%sldlinux.sys", ldlinux_path);

    /* update ADV only ? */
    if (opt.update_only == -1) {
        if (opt.reset_adv || opt.set_once) {
            modify_existing_adv(ldlinux_path);
            do_umount(mntpath, mnt_cookie);
            sync();
            rmdir(mntpath);
            exit(0);
    } else if (opt.update_only && !syslinux_already_installed(dev_fd)) {
        fprintf(stderr, "%s: no previous syslinux boot sector found\n",
                argv[0]);
        exit(1);
        } else {
            fprintf(stderr, "%s: please specify --install or --update for the future\n", argv[0]);
            opt.update_only = 0;
        }
    }

    /* Read a pre-existing ADV, if already installed */
    if (opt.reset_adv)
        syslinux_reset_adv(syslinux_adv);
    else if (read_adv(ldlinux_path, "ldlinux.sys") < 0)
        syslinux_reset_adv(syslinux_adv);
    if (modify_adv() < 0)
        exit(1);

    if ((fd = open(ldlinux_name, O_RDONLY)) >= 0) {
        uint32_t zero_attr = 0;
        ioctl(fd, FAT_IOCTL_SET_ATTRIBUTES, &zero_attr);
        close(fd);
    }

    unlink(ldlinux_name);
    fd = open(ldlinux_name, O_WRONLY | O_CREAT | O_TRUNC, 0444);
    if (fd < 0) {
        perror(opt.device);
        err = 1;
        goto umount;
    }

    /* Write it the first time */
    if (xpwrite(fd, boot_image, boot_image_len, 0) != (int)boot_image_len ||
        xpwrite(fd, syslinux_adv, 2 * ADV_SIZE,
                boot_image_len) != 2 * ADV_SIZE) {
        fprintf(stderr, "%s: write failure on %s\n", program, ldlinux_name);
        exit(1);
    }

    fsync(fd);
    /*
     * Set the attributes
     */
    {
        uint32_t attr = 0x07;   /* Hidden+System+Readonly */
        ioctl(fd, FAT_IOCTL_SET_ATTRIBUTES, &attr);
    }

    /*
     * Create a block map.
     */
    ldlinux_sectors += 2; /* 2 ADV sectors */
    sectors = calloc(ldlinux_sectors, sizeof *sectors);
    if (sectmap(fd, sectors, ldlinux_sectors)) {
        perror("bmap");
        exit(1);
    }
    close(fd);
    sync();

umount:
    do_umount(mntpath, mnt_cookie);
    sync();
    rmdir(mntpath);

    if (err)
        exit(err);

    /*
     * Patch ldlinux.sys and the boot sector
     */
    i = syslinux_patch(sectors, ldlinux_sectors, opt.stupid_mode,
                       opt.raid_mode, subdir, NULL);
    patch_sectors = (i + SECTOR_SIZE - 1) >> SECTOR_SHIFT;

    /*
     * Write the now-patched first sectors of ldlinux.sys
     */
    for (i = 0; i < patch_sectors; i++) {
        xpwrite(dev_fd, boot_image + i * SECTOR_SIZE, SECTOR_SIZE,
                opt.offset + ((off_t) sectors[i] << SECTOR_SHIFT));
    }

    /*
     * To finish up, write the boot sector
     */

    /* Read the superblock again since it might have changed while mounted */
    xpread(dev_fd, sectbuf, SECTOR_SIZE, opt.offset);

    /* Copy the syslinux code into the boot sector */
    syslinux_make_bootsect(sectbuf, fs_type);

    /* Write new boot sector */
    xpwrite(dev_fd, sectbuf, SECTOR_SIZE, opt.offset);

    close(dev_fd);
    sync();

    /* Done! */

    return 0;
}