/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (C) 1995, 1997 Wolfgang Solfrank
 * Copyright (c) 1995 Martin Husemann
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: boot.c,v 1.22 2020/01/11 16:29:07 christos Exp $");
#endif /* not lint */

#include <sys/param.h>

#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>

#include "ext.h"
#include "fsutil.h"

int
readboot(int dosfs, struct bootblock *boot)
{
        u_char block[DOSBOOTBLOCKSIZE];
        u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
        int ret = FSOK;

        if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
                perr("could not read boot block");
                return FSFATAL;
        }

        if (block[510] != 0x55 || block[511] != 0xaa) {
                pfatal("Invalid signature in boot block: %02x%02x",
                    block[511], block[510]);
                return FSFATAL;
        }

        memset(boot, 0, sizeof *boot);
        boot->ValidFat = -1;

        /* Decode BIOS Parameter Block */

        /* Bytes per sector: can only be  512, 1024, 2048 and 4096. */
        boot->bpbBytesPerSec = block[11] + (block[12] << 8);
        if (boot->bpbBytesPerSec < DOSBOOTBLOCKSIZE_REAL ||
            boot->bpbBytesPerSec > DOSBOOTBLOCKSIZE ||
            !powerof2(boot->bpbBytesPerSec)) {
                pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
                return FSFATAL;
        }

        /* Sectors per cluster: can only be: 1, 2, 4, 8, 16, 32, 64, 128. */
        boot->bpbSecPerClust = block[13];
        if (boot->bpbSecPerClust == 0 || !powerof2(boot->bpbSecPerClust)) {
                pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
                return FSFATAL;
        }

        /* Reserved sectors: must be non-zero */
        boot->bpbResSectors = block[14] + (block[15] << 8);
        if (boot->bpbResSectors < 1) {
                pfatal("Invalid reserved sectors: %u",
                    boot->bpbResSectors);
                return FSFATAL;
        }

        /* Number of FATs */
        boot->bpbFATs = block[16];
        if (boot->bpbFATs == 0) {
                pfatal("Invalid number of FATs: %u", boot->bpbFATs);
                return FSFATAL;
        }

        /* Root directory entries for FAT12 and FAT16 */
        boot->bpbRootDirEnts = block[17] + (block[18] << 8);
        if (!boot->bpbRootDirEnts) {
                /* bpbRootDirEnts = 0 suggests that we are FAT32 */
                boot->flags |= FAT32;
        }

        /* Total sectors (16 bits) */
        boot->bpbSectors = block[19] + (block[20] << 8);
        if (boot->bpbSectors != 0 && (boot->flags & FAT32)) {
                pfatal("Invalid 16-bit total sector count on FAT32: %u",
                    boot->bpbSectors);
                return FSFATAL;
        }

        /* Media type: ignored */
        boot->bpbMedia = block[21];

        /* FAT12/FAT16: 16-bit count of sectors per FAT */
        boot->bpbFATsmall = block[22] + (block[23] << 8);
        if (boot->bpbFATsmall != 0 && (boot->flags & FAT32)) {
                pfatal("Invalid 16-bit FAT sector count on FAT32: %u",
                    boot->bpbFATsmall);
                return FSFATAL;
        }

        /* Legacy CHS geometry numbers: ignored */
        boot->SecPerTrack = block[24] + (block[25] << 8);
        boot->bpbHeads = block[26] + (block[27] << 8);

        /* Hidden sectors: ignored */
        boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
            (block[30] << 16) + (block[31] << 24);

        /* Total sectors (32 bits) */
        boot->bpbHugeSectors = block[32] + (block[33] << 8) +
            (block[34] << 16) + (block[35] << 24);
        if (boot->bpbHugeSectors == 0) {
                if (boot->flags & FAT32) {
                        pfatal("FAT32 with sector count of zero");
                        return FSFATAL;
                } else if (boot->bpbSectors == 0) {
                        pfatal("FAT with sector count of zero");
                        return FSFATAL;
                }
                boot->NumSectors = boot->bpbSectors;
        } else {
                if (boot->bpbSectors != 0) {
                        pfatal("Invalid FAT sector count");
                        return FSFATAL;
                }
                boot->NumSectors = boot->bpbHugeSectors;
        }

        if (boot->flags & FAT32) {
                /* If the OEM Name field is EXFAT, it's not FAT32, so bail */
                if (!memcmp(&block[3], "EXFAT   ", 8)) {
                        pfatal("exFAT filesystem is not supported.");
                        return FSFATAL;
                }

                /* 32-bit count of sectors per FAT */
                boot->FATsecs = block[36] + (block[37] << 8)
                                + (block[38] << 16) + (block[39] << 24);

                if (block[40] & 0x80)
                        boot->ValidFat = block[40] & 0x0f;

                /* FAT32 version, bail out if not 0.0 */
                if (block[42] || block[43]) {
                        pfatal("Unknown file system version: %x.%x",
                               block[43], block[42]);
                        return FSFATAL;
                }

                /*
                 * Cluster number of the first cluster of root directory.
                 *
                 * Should be 2 but do not require it.
                 */
                boot->bpbRootClust = block[44] + (block[45] << 8)
                               + (block[46] << 16) + (block[47] << 24);

                /* Sector number of the FSInfo structure, usually 1 */
                boot->bpbFSInfo = block[48] + (block[49] << 8);

                /* Sector number of the backup boot block, ignored */
                boot->bpbBackup = block[50] + (block[51] << 8);

                /* Check basic parameters */
                if (boot->bpbFSInfo == 0) {
                        /*
                         * Either the BIOS Parameter Block has been corrupted,
                         * or this is not a FAT32 filesystem, most likely an
                         * exFAT filesystem.
                         */
                        pfatal("Invalid FAT32 Extended BIOS Parameter Block");
                        return FSFATAL;
                }

                /* Read in and verify the FSInfo block */
                if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
                    SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
                    || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
                        perr("could not read fsinfo block");
                        return FSFATAL;
                }
                if (memcmp(fsinfo, "RRaA", 4)
                    || memcmp(fsinfo + 0x1e4, "rrAa", 4)
                    || fsinfo[0x1fc]
                    || fsinfo[0x1fd]
                    || fsinfo[0x1fe] != 0x55
                    || fsinfo[0x1ff] != 0xaa
                    || fsinfo[0x3fc]
                    || fsinfo[0x3fd]
                    || fsinfo[0x3fe] != 0x55
                    || fsinfo[0x3ff] != 0xaa) {
                        pwarn("Invalid signature in fsinfo block\n");
                        if (ask(0, "Fix")) {
                                memcpy(fsinfo, "RRaA", 4);
                                memcpy(fsinfo + 0x1e4, "rrAa", 4);
                                fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
                                fsinfo[0x1fe] = 0x55;
                                fsinfo[0x1ff] = 0xaa;
                                fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
                                fsinfo[0x3fe] = 0x55;
                                fsinfo[0x3ff] = 0xaa;
                                if (lseek(dosfs, boot->bpbFSInfo *
                                    boot->bpbBytesPerSec, SEEK_SET)
                                    != boot->bpbFSInfo * boot->bpbBytesPerSec
                                    || write(dosfs, fsinfo, sizeof fsinfo)
                                    != sizeof fsinfo) {
                                        perr("Unable to write bpbFSInfo");
                                        return FSFATAL;
                                }
                                ret = FSBOOTMOD;
                        } else
                                boot->bpbFSInfo = 0;
                } else {
                        /* We appear to have a valid FSInfo block, decode */
                        boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
                                       + (fsinfo[0x1ea] << 16)
                                       + (fsinfo[0x1eb] << 24);
                        boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
                                       + (fsinfo[0x1ee] << 16)
                                       + (fsinfo[0x1ef] << 24);
                }
        } else {
                /* !FAT32: FAT12/FAT16 */
                boot->FATsecs = boot->bpbFATsmall;
        }

        if (boot->FATsecs < 1 || boot->FATsecs > UINT32_MAX / boot->bpbFATs) {
                pfatal("Invalid FATs(%u) with FATsecs(%zu)",
                        boot->bpbFATs, (size_t)boot->FATsecs);
                return FSFATAL;
        }

        boot->FirstCluster = (boot->bpbRootDirEnts * 32 +
            boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
            boot->bpbResSectors + boot->bpbFATs * boot->FATsecs;

        if (boot->FirstCluster + boot->bpbSecPerClust > boot->NumSectors) {
                pfatal("Cluster offset too large (%u clusters)\n",
                    boot->FirstCluster);
                return FSFATAL;
        }

        /*
         * The number of clusters is derived from available data sectors,
         * divided by sectors per cluster.
         */
        boot->NumClusters =
            (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust;

        if (boot->flags & FAT32) {
                if (boot->NumClusters > (CLUST_RSRVD & CLUST32_MASK)) {
                        pfatal("Filesystem too big (%u clusters) for FAT32 partition",
                            boot->NumClusters);
                        return FSFATAL;
                }
                if (boot->NumClusters < (CLUST_RSRVD & CLUST16_MASK)) {
                        pfatal("Filesystem too small (%u clusters) for FAT32 partition",
                            boot->NumClusters);
                        return FSFATAL;
                }
                boot->ClustMask = CLUST32_MASK;

                if (boot->bpbRootClust < CLUST_FIRST ||
                    boot->bpbRootClust >= boot->NumClusters) {
                        pfatal("Root directory starts with cluster out of range(%u)",
                               boot->bpbRootClust);
                        return FSFATAL;
                }
        } else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK)) {
                boot->ClustMask = CLUST12_MASK;
        } else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK)) {
                boot->ClustMask = CLUST16_MASK;
        } else {
                pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
                       boot->NumClusters);
                return FSFATAL;
        }

        switch (boot->ClustMask) {
        case CLUST32_MASK:
                boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4;
                break;
        case CLUST16_MASK:
                boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2;
                break;
        default:
                boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3;
                break;
        }

        if (boot->NumFatEntries < boot->NumClusters) {
                pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
                       boot->NumClusters, boot->FATsecs);
                return FSFATAL;
        }

        /*
         * There are two reserved clusters. To avoid adding CLUST_FIRST every
         * time we perform boundary checks, we increment the NumClusters by 2,
         * which is CLUST_FIRST to denote the first out-of-range cluster number.
         */
        boot->NumClusters += CLUST_FIRST;

        boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust;

        boot->NumFiles = 1;
        boot->NumFree = 0;

        return ret;
}

int
writefsinfo(int dosfs, struct bootblock *boot)
{
        u_char fsinfo[2 * DOSBOOTBLOCKSIZE];

        if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
            != boot->bpbFSInfo * boot->bpbBytesPerSec
            || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
                perr("could not read fsinfo block");
                return FSFATAL;
        }
        fsinfo[0x1e8] = (u_char)boot->FSFree;
        fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
        fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
        fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
        fsinfo[0x1ec] = (u_char)boot->FSNext;
        fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
        fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
        fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
        if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
            != boot->bpbFSInfo * boot->bpbBytesPerSec
            || write(dosfs, fsinfo, sizeof fsinfo)
            != sizeof fsinfo) {
                perr("Unable to write bpbFSInfo");
                return FSFATAL;
        }
        /*
         * Technically, we should return FSBOOTMOD here.
         *
         * However, since Win95 OSR2 (the first M$ OS that has
         * support for FAT32) doesn't maintain the FSINFO block
         * correctly, it has to be fixed pretty often.
         *
         * Therefore, we handle the FSINFO block only informally,
         * fixing it if necessary, but otherwise ignoring the
         * fact that it was incorrect.
         */
        return 0;
}