1/*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (C) 1995, 1997 Wolfgang Solfrank 5 * Copyright (c) 1995 Martin Husemann 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 29#include <sys/cdefs.h> 30#ifndef lint 31__RCSID("$NetBSD: boot.c,v 1.22 2020/01/11 16:29:07 christos Exp $"); 32static const char rcsid[] = 33 "$FreeBSD$"; 34#endif /* not lint */ 35 36#include <sys/param.h> 37 38#include <stdint.h> 39#include <stdlib.h> 40#include <string.h> 41#include <stdio.h> 42#include <unistd.h> 43 44#include "ext.h" 45#include "fsutil.h" 46 47int 48readboot(int dosfs, struct bootblock *boot) 49{ 50 u_char block[DOSBOOTBLOCKSIZE]; 51 u_char fsinfo[2 * DOSBOOTBLOCKSIZE]; 52 int ret = FSOK; 53 54 if ((size_t)read(dosfs, block, sizeof block) != sizeof block) { 55 perr("could not read boot block"); 56 return FSFATAL; 57 } 58 59 if (block[510] != 0x55 || block[511] != 0xaa) { 60 pfatal("Invalid signature in boot block: %02x%02x", 61 block[511], block[510]); 62 return FSFATAL; 63 } 64 65 memset(boot, 0, sizeof *boot); 66 boot->ValidFat = -1; 67 68 /* Decode BIOS Parameter Block */ 69 70 /* Bytes per sector: can only be 512, 1024, 2048 and 4096. */ 71 boot->bpbBytesPerSec = block[11] + (block[12] << 8); 72 if (boot->bpbBytesPerSec < DOSBOOTBLOCKSIZE_REAL || 73 boot->bpbBytesPerSec > DOSBOOTBLOCKSIZE || 74 !powerof2(boot->bpbBytesPerSec)) { 75 pfatal("Invalid sector size: %u", boot->bpbBytesPerSec); 76 return FSFATAL; 77 } 78 79 /* Sectors per cluster: can only be: 1, 2, 4, 8, 16, 32, 64, 128. */ 80 boot->bpbSecPerClust = block[13]; 81 if (boot->bpbSecPerClust == 0 || !powerof2(boot->bpbSecPerClust)) { 82 pfatal("Invalid cluster size: %u", boot->bpbSecPerClust); 83 return FSFATAL; 84 } 85 86 /* Reserved sectors: must be non-zero */ 87 boot->bpbResSectors = block[14] + (block[15] << 8); 88 if (boot->bpbResSectors < 1) { 89 pfatal("Invalid reserved sectors: %u", 90 boot->bpbResSectors); 91 return FSFATAL; 92 } 93 94 /* Number of FATs */ 95 boot->bpbFATs = block[16]; 96 if (boot->bpbFATs == 0) { 97 pfatal("Invalid number of FATs: %u", boot->bpbFATs); 98 return FSFATAL; 99 } 100 101 /* Root directory entries for FAT12 and FAT16 */ 102 boot->bpbRootDirEnts = block[17] + (block[18] << 8); 103 if (!boot->bpbRootDirEnts) { 104 /* bpbRootDirEnts = 0 suggests that we are FAT32 */ 105 boot->flags |= FAT32; 106 } 107 108 /* Total sectors (16 bits) */ 109 boot->bpbSectors = block[19] + (block[20] << 8); 110 if (boot->bpbSectors != 0 && (boot->flags & FAT32)) { 111 pfatal("Invalid 16-bit total sector count on FAT32: %u", 112 boot->bpbSectors); 113 return FSFATAL; 114 } 115 116 /* Media type: ignored */ 117 boot->bpbMedia = block[21]; 118 119 /* FAT12/FAT16: 16-bit count of sectors per FAT */ 120 boot->bpbFATsmall = block[22] + (block[23] << 8); 121 if (boot->bpbFATsmall != 0 && (boot->flags & FAT32)) { 122 pfatal("Invalid 16-bit FAT sector count on FAT32: %u", 123 boot->bpbFATsmall); 124 return FSFATAL; 125 } 126 127 /* Legacy CHS geometry numbers: ignored */ 128 boot->SecPerTrack = block[24] + (block[25] << 8); 129 boot->bpbHeads = block[26] + (block[27] << 8); 130 131 /* Hidden sectors: ignored */ 132 boot->bpbHiddenSecs = block[28] + (block[29] << 8) + 133 (block[30] << 16) + (block[31] << 24); 134 135 /* Total sectors (32 bits) */ 136 boot->bpbHugeSectors = block[32] + (block[33] << 8) + 137 (block[34] << 16) + (block[35] << 24); 138 if (boot->bpbHugeSectors == 0) { 139 if (boot->flags & FAT32) { 140 pfatal("FAT32 with sector count of zero"); 141 return FSFATAL; 142 } else if (boot->bpbSectors == 0) { 143 pfatal("FAT with sector count of zero"); 144 return FSFATAL; 145 } 146 boot->NumSectors = boot->bpbSectors; 147 } else { 148 if (boot->bpbSectors != 0) { 149 pfatal("Invalid FAT sector count"); 150 return FSFATAL; 151 } 152 boot->NumSectors = boot->bpbHugeSectors; 153 } 154 155 if (boot->flags & FAT32) { 156 /* If the OEM Name field is EXFAT, it's not FAT32, so bail */ 157 if (!memcmp(&block[3], "EXFAT ", 8)) { 158 pfatal("exFAT filesystem is not supported."); 159 return FSFATAL; 160 } 161 162 /* 32-bit count of sectors per FAT */ 163 boot->FATsecs = block[36] + (block[37] << 8) 164 + (block[38] << 16) + (block[39] << 24); 165 166 if (block[40] & 0x80) 167 boot->ValidFat = block[40] & 0x0f; 168 169 /* FAT32 version, bail out if not 0.0 */ 170 if (block[42] || block[43]) { 171 pfatal("Unknown file system version: %x.%x", 172 block[43], block[42]); 173 return FSFATAL; 174 } 175 176 /* 177 * Cluster number of the first cluster of root directory. 178 * 179 * Should be 2 but do not require it. 180 */ 181 boot->bpbRootClust = block[44] + (block[45] << 8) 182 + (block[46] << 16) + (block[47] << 24); 183 184 /* Sector number of the FSInfo structure, usually 1 */ 185 boot->bpbFSInfo = block[48] + (block[49] << 8); 186 187 /* Sector number of the backup boot block, ignored */ 188 boot->bpbBackup = block[50] + (block[51] << 8); 189 190 /* Check basic parameters */ 191 if (boot->bpbFSInfo == 0) { 192 /* 193 * Either the BIOS Parameter Block has been corrupted, 194 * or this is not a FAT32 filesystem, most likely an 195 * exFAT filesystem. 196 */ 197 pfatal("Invalid FAT32 Extended BIOS Parameter Block"); 198 return FSFATAL; 199 } 200 201 /* Read in and verify the FSInfo block */ 202 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, 203 SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec 204 || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) { 205 perr("could not read fsinfo block"); 206 return FSFATAL; 207 } 208 if (memcmp(fsinfo, "RRaA", 4) 209 || memcmp(fsinfo + 0x1e4, "rrAa", 4) 210 || fsinfo[0x1fc] 211 || fsinfo[0x1fd] 212 || fsinfo[0x1fe] != 0x55 213 || fsinfo[0x1ff] != 0xaa 214 || fsinfo[0x3fc] 215 || fsinfo[0x3fd] 216 || fsinfo[0x3fe] != 0x55 217 || fsinfo[0x3ff] != 0xaa) { 218 pwarn("Invalid signature in fsinfo block\n"); 219 if (ask(0, "Fix")) { 220 memcpy(fsinfo, "RRaA", 4); 221 memcpy(fsinfo + 0x1e4, "rrAa", 4); 222 fsinfo[0x1fc] = fsinfo[0x1fd] = 0; 223 fsinfo[0x1fe] = 0x55; 224 fsinfo[0x1ff] = 0xaa; 225 fsinfo[0x3fc] = fsinfo[0x3fd] = 0; 226 fsinfo[0x3fe] = 0x55; 227 fsinfo[0x3ff] = 0xaa; 228 if (lseek(dosfs, boot->bpbFSInfo * 229 boot->bpbBytesPerSec, SEEK_SET) 230 != boot->bpbFSInfo * boot->bpbBytesPerSec 231 || write(dosfs, fsinfo, sizeof fsinfo) 232 != sizeof fsinfo) { 233 perr("Unable to write bpbFSInfo"); 234 return FSFATAL; 235 } 236 ret = FSBOOTMOD; 237 } else 238 boot->bpbFSInfo = 0; 239 } else { 240 /* We appear to have a valid FSInfo block, decode */ 241 boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8) 242 + (fsinfo[0x1ea] << 16) 243 + (fsinfo[0x1eb] << 24); 244 boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8) 245 + (fsinfo[0x1ee] << 16) 246 + (fsinfo[0x1ef] << 24); 247 } 248 } else { 249 /* !FAT32: FAT12/FAT16 */ 250 boot->FATsecs = boot->bpbFATsmall; 251 } 252 253 if (boot->FATsecs < 1 || boot->FATsecs > UINT32_MAX / boot->bpbFATs) { 254 pfatal("Invalid FATs(%u) with FATsecs(%zu)", 255 boot->bpbFATs, (size_t)boot->FATsecs); 256 return FSFATAL; 257 } 258 259 boot->FirstCluster = (boot->bpbRootDirEnts * 32 + 260 boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec + 261 boot->bpbResSectors + boot->bpbFATs * boot->FATsecs; 262 263 if (boot->FirstCluster + boot->bpbSecPerClust > boot->NumSectors) { 264 pfatal("Cluster offset too large (%u clusters)\n", 265 boot->FirstCluster); 266 return FSFATAL; 267 } 268 269 /* 270 * The number of clusters is derived from available data sectors, 271 * divided by sectors per cluster. 272 */ 273 boot->NumClusters = 274 (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust; 275 276 if (boot->flags & FAT32) { 277 if (boot->NumClusters > (CLUST_RSRVD & CLUST32_MASK)) { 278 pfatal("Filesystem too big (%u clusters) for FAT32 partition", 279 boot->NumClusters); 280 return FSFATAL; 281 } 282 if (boot->NumClusters < (CLUST_RSRVD & CLUST16_MASK)) { 283 pfatal("Filesystem too small (%u clusters) for FAT32 partition", 284 boot->NumClusters); 285 return FSFATAL; 286 } 287 boot->ClustMask = CLUST32_MASK; 288 289 if (boot->bpbRootClust < CLUST_FIRST || 290 boot->bpbRootClust >= boot->NumClusters) { 291 pfatal("Root directory starts with cluster out of range(%u)", 292 boot->bpbRootClust); 293 return FSFATAL; 294 } 295 } else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK)) { 296 boot->ClustMask = CLUST12_MASK; 297 } else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK)) { 298 boot->ClustMask = CLUST16_MASK; 299 } else { 300 pfatal("Filesystem too big (%u clusters) for non-FAT32 partition", 301 boot->NumClusters); 302 return FSFATAL; 303 } 304 305 switch (boot->ClustMask) { 306 case CLUST32_MASK: 307 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4; 308 break; 309 case CLUST16_MASK: 310 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2; 311 break; 312 default: 313 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3; 314 break; 315 } 316 317 if (boot->NumFatEntries < boot->NumClusters) { 318 pfatal("FAT size too small, %u entries won't fit into %u sectors\n", 319 boot->NumClusters, boot->FATsecs); 320 return FSFATAL; 321 } 322 323 /* 324 * There are two reserved clusters. To avoid adding CLUST_FIRST every 325 * time we perform boundary checks, we increment the NumClusters by 2, 326 * which is CLUST_FIRST to denote the first out-of-range cluster number. 327 */ 328 boot->NumClusters += CLUST_FIRST; 329 330 boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust; 331 332 boot->NumFiles = 1; 333 boot->NumFree = 0; 334 335 return ret; 336} 337 338int 339writefsinfo(int dosfs, struct bootblock *boot) 340{ 341 u_char fsinfo[2 * DOSBOOTBLOCKSIZE]; 342 343 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET) 344 != boot->bpbFSInfo * boot->bpbBytesPerSec 345 || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) { 346 perr("could not read fsinfo block"); 347 return FSFATAL; 348 } 349 fsinfo[0x1e8] = (u_char)boot->FSFree; 350 fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8); 351 fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16); 352 fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24); 353 fsinfo[0x1ec] = (u_char)boot->FSNext; 354 fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8); 355 fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16); 356 fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24); 357 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET) 358 != boot->bpbFSInfo * boot->bpbBytesPerSec 359 || write(dosfs, fsinfo, sizeof fsinfo) 360 != sizeof fsinfo) { 361 perr("Unable to write bpbFSInfo"); 362 return FSFATAL; 363 } 364 /* 365 * Technically, we should return FSBOOTMOD here. 366 * 367 * However, since Win95 OSR2 (the first M$ OS that has 368 * support for FAT32) doesn't maintain the FSINFO block 369 * correctly, it has to be fixed pretty often. 370 * 371 * Therefore, we handle the FSINFO block only informally, 372 * fixing it if necessary, but otherwise ignoring the 373 * fact that it was incorrect. 374 */ 375 return 0; 376} 377