/*      $OpenBSD: boot.c,v 1.24 2016/10/10 00:34:50 bluhm Exp $ */
/*      $NetBSD: boot.c,v 1.5 1997/10/17 11:19:23 ws Exp $      */

/*
 * 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/param.h>  /* DEV_BSIZE powerof2 */
#include <sys/disklabel.h>

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

#include "ext.h"

int
readboot(int dosfs, struct bootblock *boot)
{
        u_char *block = NULL;
        u_char *fsinfo = NULL;
        u_char *backup = NULL;
        int ret = FSOK, secsize = lab.d_secsize, fsinfosz;
        off_t o;
        ssize_t n;

        if (secsize < DOSBOOTBLOCKSIZE) {
                xperror("sector size < DOSBOOTBLOCKSIZE");
                goto fail;
        }
        if (DOSBOOTBLOCKSIZE != DEV_BSIZE) {
                xperror("DOSBOOTBLOCKSIZE != DEV_BSIZE");
                goto fail;
        }

        block = malloc(secsize);
        if (block == NULL) {
                xperror("could not malloc boot block");
                goto fail;
        }

        if ((o = lseek(dosfs, 0, SEEK_SET)) == -1) {
                xperror("could not seek boot block");
                goto fail;
        }

        n = read(dosfs, block, secsize);
        if (n == -1 || n != secsize) {
                xperror("could not read boot block");
                goto fail;
        }

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

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

        /* decode bios parameter block */
        boot->BytesPerSec = block[11] + (block[12] << 8);
        if (boot->BytesPerSec == 0 || boot->BytesPerSec != secsize) {
                pfatal("Invalid sector size: %u\n", boot->BytesPerSec);
                goto fail;
        }
        boot->SecPerClust = block[13];
        if (boot->SecPerClust == 0 || !powerof2(boot->SecPerClust)) {
                pfatal("Invalid cluster size: %u\n", boot->SecPerClust);
                goto fail;
        }
        boot->ResSectors = block[14] + (block[15] << 8);
        boot->FATs = block[16];
        if (boot->FATs == 0) {
                pfatal("Invalid number of FATs: %u\n", boot->FATs);
                goto fail;
        }
        boot->RootDirEnts = block[17] + (block[18] << 8);
        boot->Sectors = block[19] + (block[20] << 8);
        boot->Media = block[21];
        boot->FATsmall = block[22] + (block[23] << 8);
        boot->SecPerTrack = block[24] + (block[25] << 8);
        boot->Heads = block[26] + (block[27] << 8);
        boot->HiddenSecs = block[28] + (block[29] << 8) + (block[30] << 16) + (block[31] << 24);
        boot->HugeSectors = block[32] + (block[33] << 8) + (block[34] << 16) + (block[35] << 24);

        boot->FATsecs = boot->FATsmall;

        if (!boot->RootDirEnts) {
                boot->flags |= FAT32;
                boot->FATsecs = block[36] + (block[37] << 8)
                                + (block[38] << 16) + (block[39] << 24);
                if (block[40] & 0x80)
                        boot->ValidFat = block[40] & 0x0f;

                /* check version number: */
                if (block[42] || block[43]) {
                        /* Correct?                             XXX */
                        pfatal("Unknown filesystem version: %x.%x\n",
                               block[43], block[42]);
                        goto fail;
                }
                boot->RootCl = block[44] + (block[45] << 8)
                               + (block[46] << 16) + (block[47] << 24);
                boot->FSInfo = block[48] + (block[49] << 8);
                boot->Backup = block[50] + (block[51] << 8);

                o = lseek(dosfs, boot->FSInfo * secsize, SEEK_SET);
                if (o == -1 || o != boot->FSInfo * secsize) {
                        xperror("could not seek fsinfo block");
                        goto fail;
                }

                if ((2 * DOSBOOTBLOCKSIZE) < secsize)
                        fsinfosz = secsize;
                else
                        fsinfosz = 2 * secsize;
                fsinfo = malloc(fsinfosz);
                if (fsinfo == NULL) {
                        xperror("could not malloc fsinfo");
                        goto fail;
                }
                n = read(dosfs, fsinfo, fsinfosz);
                if (n == -1 || n != fsinfosz) {
                        xperror("could not read fsinfo block");
                        goto fail;
                }

                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;

                                o = lseek(dosfs, boot->FSInfo * secsize,
                                    SEEK_SET);
                                if (o == -1 || o != boot->FSInfo * secsize) {
                                        xperror("Unable to seek FSInfo");
                                        goto fail;
                                }
                                n = write(dosfs, fsinfo, fsinfosz);
                                if (n == -1 || n != fsinfosz) {
                                        xperror("Unable to write FSInfo");
                                        goto fail;
                                }
                                ret = FSBOOTMOD;
                        } else
                                boot->FSInfo = 0;
                }
                if (boot->FSInfo) {
                        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);
                }

                o = lseek(dosfs, boot->Backup * secsize, SEEK_SET);
                if (o == -1 || o != boot->Backup * secsize) {
                        xperror("could not seek backup bootblock");
                        goto fail;
                }
                backup = malloc(2 * secsize); /* In case we check fsinfo. */
                if (backup == NULL) {
                        xperror("could not malloc backup boot block");
                        goto fail;
                }
                n = read(dosfs, backup, secsize);
                if (n == -1 || n != secsize) {
                        xperror("could not read backup bootblock");
                        goto fail;
                }

                /*
                 * Check that the backup boot block matches the primary one.
                 * We don't check every byte, since some vendor utilities
                 * seem to overwrite the boot code when they feel like it,
                 * without changing the backup block.  Specifically, we check
                 * the two-byte signature at the end, the BIOS parameter
                 * block (which starts after the 3-byte JMP and the 8-byte
                 * OEM name/version) and the filesystem information that
                 * follows the BPB (bsBPB[53] and bsExt[26] for FAT32, so we
                 * check 79 bytes).
                 */
                if (backup[510] != 0x55 || backup[511] != 0xaa) {
                        pfatal("Invalid signature in backup boot block: %02x%02x\n", backup[511], backup[510]);
                }
                if (memcmp(block + 11, backup + 11, 79)) {
                        pfatal("backup doesn't compare to primary bootblock\n");
                        goto fail;
                }
                /* Check backup FSInfo?                                 XXX */
        }

        if (boot->FATsecs == 0) {
                pfatal("Invalid number of FAT sectors: %u\n", boot->FATsecs);
                goto fail;
        }

        boot->ClusterOffset = (boot->RootDirEnts * 32 + secsize - 1)
            / secsize
            + boot->ResSectors
            + boot->FATs * boot->FATsecs
            - CLUST_FIRST * boot->SecPerClust;

        if (boot->Sectors) {
                boot->HugeSectors = 0;
                boot->NumSectors = boot->Sectors;
        } else
                boot->NumSectors = boot->HugeSectors;

        if (boot->ClusterOffset > boot->NumSectors) {
                pfatal("Cluster offset too large (%u clusters)\n",
                    boot->ClusterOffset);
                goto fail;
        }
        boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) / boot->SecPerClust;

        if (boot->flags&FAT32)
                boot->ClustMask = CLUST32_MASK;
        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\n",
                       boot->NumClusters);
                goto fail;
        }

        switch (boot->ClustMask) {
        case CLUST32_MASK:
                boot->NumFatEntries = (boot->FATsecs * secsize) / 4;
                break;
        case CLUST16_MASK:
                boot->NumFatEntries = (boot->FATsecs * secsize) / 2;
                break;
        default:
                boot->NumFatEntries = (boot->FATsecs * secsize * 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);
                goto fail;
        }
        boot->ClusterSize = boot->SecPerClust * secsize;

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

        free(backup);
        free(block);
        free(fsinfo);
        return ret;
fail:
        free(backup);
        free(block);
        free(fsinfo);
        return FSFATAL;
}

int
writefsinfo(int dosfs, struct bootblock *boot)
{
        u_char *fsinfo = NULL;
        int secsize = lab.d_secsize, fsinfosz;
        off_t o;
        ssize_t n;

        if ((2 * DOSBOOTBLOCKSIZE) < secsize)
                fsinfosz = secsize;
        else
                fsinfosz = 2 * secsize;

        fsinfo = malloc(fsinfosz);
        if (fsinfo == NULL) {
                xperror("could not malloc fsinfo block");
                goto fail;
        }

        o = lseek(dosfs, boot->FSInfo * secsize, SEEK_SET);
        if (o == -1 || o != boot->FSInfo * secsize) {
                xperror("could not seek fsinfo block");
                goto fail;
        }

        n = read(dosfs, fsinfo, fsinfosz);
        if (n == -1 || n != fsinfosz) {
                xperror("could not read fsinfo block");
                goto fail;
        }

        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);

        o = lseek(dosfs, o, SEEK_SET);
        if (o == -1 || o != boot->FSInfo * boot->BytesPerSec) {
                xperror("Unable to seek FSInfo");
                goto fail;
        }
        n = write(dosfs, fsinfo, fsinfosz);
        if (n == -1 || n != fsinfosz) {
                xperror("Unable to write FSInfo");
                goto fail;
        }

        free(fsinfo);

        /*
         * 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;
fail:
        free(fsinfo);
        return FSFATAL;
}