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