1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 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 $"); 32 #endif /* not lint */ 33 34 #include <sys/param.h> 35 #include <sys/endian.h> 36 37 #include <stdint.h> 38 #include <stdlib.h> 39 #include <string.h> 40 #include <stdio.h> 41 #include <unistd.h> 42 43 #include "ext.h" 44 #include "fsutil.h" 45 46 int 47 readboot(int dosfs, struct bootblock *boot) 48 { 49 u_char block[DOSBOOTBLOCKSIZE]; 50 u_char fsinfo[2 * DOSBOOTBLOCKSIZE]; 51 int ret = FSOK; 52 53 if ((size_t)read(dosfs, block, sizeof block) != sizeof block) { 54 perr("could not read boot block"); 55 return FSFATAL; 56 } 57 58 if (block[510] != 0x55 || block[511] != 0xaa) { 59 pfatal("Invalid signature in boot block: %02x%02x", 60 block[511], block[510]); 61 return FSFATAL; 62 } 63 64 memset(boot, 0, sizeof *boot); 65 boot->ValidFat = -1; 66 67 /* Decode BIOS Parameter Block */ 68 69 /* Bytes per sector: can only be 512, 1024, 2048 and 4096. */ 70 boot->bpbBytesPerSec = block[11] + (block[12] << 8); 71 if (boot->bpbBytesPerSec < DOSBOOTBLOCKSIZE_REAL || 72 boot->bpbBytesPerSec > DOSBOOTBLOCKSIZE || 73 !powerof2(boot->bpbBytesPerSec)) { 74 pfatal("Invalid sector size: %u", boot->bpbBytesPerSec); 75 return FSFATAL; 76 } 77 78 /* Sectors per cluster: can only be: 1, 2, 4, 8, 16, 32, 64, 128. */ 79 boot->bpbSecPerClust = block[13]; 80 if (boot->bpbSecPerClust == 0 || !powerof2(boot->bpbSecPerClust)) { 81 pfatal("Invalid cluster size: %u", boot->bpbSecPerClust); 82 return FSFATAL; 83 } 84 85 /* Reserved sectors: must be non-zero */ 86 boot->bpbResSectors = block[14] + (block[15] << 8); 87 if (boot->bpbResSectors < 1) { 88 pfatal("Invalid reserved sectors: %u", 89 boot->bpbResSectors); 90 return FSFATAL; 91 } 92 93 /* Number of FATs */ 94 boot->bpbFATs = block[16]; 95 if (boot->bpbFATs == 0) { 96 pfatal("Invalid number of FATs: %u", boot->bpbFATs); 97 return FSFATAL; 98 } 99 100 /* Root directory entries for FAT12 and FAT16 */ 101 boot->bpbRootDirEnts = block[17] + (block[18] << 8); 102 if (!boot->bpbRootDirEnts) { 103 /* bpbRootDirEnts = 0 suggests that we are FAT32 */ 104 boot->flags |= FAT32; 105 } 106 107 /* Total sectors (16 bits) */ 108 boot->bpbSectors = block[19] + (block[20] << 8); 109 if (boot->bpbSectors != 0 && (boot->flags & FAT32)) { 110 pfatal("Invalid 16-bit total sector count on FAT32: %u", 111 boot->bpbSectors); 112 return FSFATAL; 113 } 114 115 /* Media type: ignored */ 116 boot->bpbMedia = block[21]; 117 118 /* FAT12/FAT16: 16-bit count of sectors per FAT */ 119 boot->bpbFATsmall = block[22] + (block[23] << 8); 120 if (boot->bpbFATsmall != 0 && (boot->flags & FAT32)) { 121 pfatal("Invalid 16-bit FAT sector count on FAT32: %u", 122 boot->bpbFATsmall); 123 return FSFATAL; 124 } 125 126 /* Legacy CHS geometry numbers: ignored */ 127 boot->SecPerTrack = block[24] + (block[25] << 8); 128 boot->bpbHeads = block[26] + (block[27] << 8); 129 130 /* Hidden sectors: ignored */ 131 boot->bpbHiddenSecs = le32dec(&block[28]); 132 133 /* Total sectors (32 bits) */ 134 boot->bpbHugeSectors = le32dec(&block[32]); 135 if (boot->bpbHugeSectors == 0) { 136 if (boot->flags & FAT32) { 137 pfatal("FAT32 with sector count of zero"); 138 return FSFATAL; 139 } else if (boot->bpbSectors == 0) { 140 pfatal("FAT with sector count of zero"); 141 return FSFATAL; 142 } 143 boot->NumSectors = boot->bpbSectors; 144 } else { 145 if (boot->bpbSectors != 0) { 146 pfatal("Invalid FAT sector count"); 147 return FSFATAL; 148 } 149 boot->NumSectors = boot->bpbHugeSectors; 150 } 151 152 if (boot->flags & FAT32) { 153 /* If the OEM Name field is EXFAT, it's not FAT32, so bail */ 154 if (!memcmp(&block[3], "EXFAT ", 8)) { 155 pfatal("exFAT filesystem is not supported."); 156 return FSFATAL; 157 } 158 159 /* 32-bit count of sectors per FAT */ 160 boot->FATsecs = le32dec(&block[36]); 161 162 if (block[40] & 0x80) 163 boot->ValidFat = block[40] & 0x0f; 164 165 /* FAT32 version, bail out if not 0.0 */ 166 if (block[42] || block[43]) { 167 pfatal("Unknown file system version: %x.%x", 168 block[43], block[42]); 169 return FSFATAL; 170 } 171 172 /* 173 * Cluster number of the first cluster of root directory. 174 * 175 * Should be 2 but do not require it. 176 */ 177 boot->bpbRootClust = le32dec(&block[44]); 178 179 /* Sector number of the FSInfo structure, usually 1 */ 180 boot->bpbFSInfo = block[48] + (block[49] << 8); 181 182 /* Sector number of the backup boot block, ignored */ 183 boot->bpbBackup = block[50] + (block[51] << 8); 184 185 /* Check basic parameters */ 186 if (boot->bpbFSInfo == 0) { 187 /* 188 * Either the BIOS Parameter Block has been corrupted, 189 * or this is not a FAT32 filesystem, most likely an 190 * exFAT filesystem. 191 */ 192 pfatal("Invalid FAT32 Extended BIOS Parameter Block"); 193 return FSFATAL; 194 } 195 196 /* Read in and verify the FSInfo block */ 197 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, 198 SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec 199 || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) { 200 perr("could not read fsinfo block"); 201 return FSFATAL; 202 } 203 if (memcmp(fsinfo, "RRaA", 4) 204 || memcmp(fsinfo + 0x1e4, "rrAa", 4) 205 || fsinfo[0x1fc] 206 || fsinfo[0x1fd] 207 || fsinfo[0x1fe] != 0x55 208 || fsinfo[0x1ff] != 0xaa 209 || fsinfo[0x3fc] 210 || fsinfo[0x3fd] 211 || fsinfo[0x3fe] != 0x55 212 || fsinfo[0x3ff] != 0xaa) { 213 pwarn("Invalid signature in fsinfo block\n"); 214 if (ask(0, "Fix")) { 215 memcpy(fsinfo, "RRaA", 4); 216 memcpy(fsinfo + 0x1e4, "rrAa", 4); 217 fsinfo[0x1fc] = fsinfo[0x1fd] = 0; 218 fsinfo[0x1fe] = 0x55; 219 fsinfo[0x1ff] = 0xaa; 220 fsinfo[0x3fc] = fsinfo[0x3fd] = 0; 221 fsinfo[0x3fe] = 0x55; 222 fsinfo[0x3ff] = 0xaa; 223 if (lseek(dosfs, boot->bpbFSInfo * 224 boot->bpbBytesPerSec, SEEK_SET) 225 != boot->bpbFSInfo * boot->bpbBytesPerSec 226 || write(dosfs, fsinfo, sizeof fsinfo) 227 != sizeof fsinfo) { 228 perr("Unable to write bpbFSInfo"); 229 return FSFATAL; 230 } 231 ret = FSBOOTMOD; 232 } else 233 boot->bpbFSInfo = 0; 234 } else { 235 /* We appear to have a valid FSInfo block, decode */ 236 boot->FSFree = le32dec(&fsinfo[0x1e8]); 237 boot->FSNext = le32dec(&fsinfo[0x1ec]); 238 } 239 } else { 240 /* !FAT32: FAT12/FAT16 */ 241 boot->FATsecs = boot->bpbFATsmall; 242 } 243 244 if (boot->FATsecs < 1 || boot->FATsecs > UINT32_MAX / boot->bpbFATs) { 245 pfatal("Invalid FATs(%u) with FATsecs(%zu)", 246 boot->bpbFATs, (size_t)boot->FATsecs); 247 return FSFATAL; 248 } 249 250 boot->FirstCluster = (boot->bpbRootDirEnts * 32 + 251 boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec + 252 boot->bpbResSectors + boot->bpbFATs * boot->FATsecs; 253 254 if (boot->FirstCluster + boot->bpbSecPerClust > boot->NumSectors) { 255 pfatal("Cluster offset too large (%u clusters)\n", 256 boot->FirstCluster); 257 return FSFATAL; 258 } 259 260 /* 261 * The number of clusters is derived from available data sectors, 262 * divided by sectors per cluster. 263 */ 264 boot->NumClusters = 265 (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust; 266 267 if (boot->flags & FAT32) { 268 if (boot->NumClusters > (CLUST_RSRVD & CLUST32_MASK)) { 269 pfatal("Filesystem too big (%u clusters) for FAT32 partition", 270 boot->NumClusters); 271 return FSFATAL; 272 } 273 if (boot->NumClusters < (CLUST_RSRVD & CLUST16_MASK)) { 274 pfatal("Filesystem too small (%u clusters) for FAT32 partition", 275 boot->NumClusters); 276 return FSFATAL; 277 } 278 boot->ClustMask = CLUST32_MASK; 279 280 if (boot->bpbRootClust < CLUST_FIRST || 281 boot->bpbRootClust >= boot->NumClusters) { 282 pfatal("Root directory starts with cluster out of range(%u)", 283 boot->bpbRootClust); 284 return FSFATAL; 285 } 286 } else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK)) { 287 boot->ClustMask = CLUST12_MASK; 288 } else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK)) { 289 boot->ClustMask = CLUST16_MASK; 290 } else { 291 pfatal("Filesystem too big (%u clusters) for non-FAT32 partition", 292 boot->NumClusters); 293 return FSFATAL; 294 } 295 296 switch (boot->ClustMask) { 297 case CLUST32_MASK: 298 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4; 299 break; 300 case CLUST16_MASK: 301 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2; 302 break; 303 default: 304 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3; 305 break; 306 } 307 308 if (boot->NumFatEntries < boot->NumClusters) { 309 pfatal("FAT size too small, %u entries won't fit into %u sectors\n", 310 boot->NumClusters, boot->FATsecs); 311 return FSFATAL; 312 } 313 314 /* 315 * There are two reserved clusters. To avoid adding CLUST_FIRST every 316 * time we perform boundary checks, we increment the NumClusters by 2, 317 * which is CLUST_FIRST to denote the first out-of-range cluster number. 318 */ 319 boot->NumClusters += CLUST_FIRST; 320 321 boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust; 322 323 boot->NumFiles = 1; 324 boot->NumFree = 0; 325 326 return ret; 327 } 328 329 int 330 writefsinfo(int dosfs, struct bootblock *boot) 331 { 332 u_char fsinfo[2 * DOSBOOTBLOCKSIZE]; 333 334 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET) 335 != boot->bpbFSInfo * boot->bpbBytesPerSec 336 || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) { 337 perr("could not read fsinfo block"); 338 return FSFATAL; 339 } 340 fsinfo[0x1e8] = (u_char)boot->FSFree; 341 fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8); 342 fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16); 343 fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24); 344 fsinfo[0x1ec] = (u_char)boot->FSNext; 345 fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8); 346 fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16); 347 fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24); 348 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET) 349 != boot->bpbFSInfo * boot->bpbBytesPerSec 350 || write(dosfs, fsinfo, sizeof fsinfo) 351 != sizeof fsinfo) { 352 perr("Unable to write bpbFSInfo"); 353 return FSFATAL; 354 } 355 /* 356 * Technically, we should return FSBOOTMOD here. 357 * 358 * However, since Win95 OSR2 (the first M$ OS that has 359 * support for FAT32) doesn't maintain the FSINFO block 360 * correctly, it has to be fixed pretty often. 361 * 362 * Therefore, we handle the FSINFO block only informally, 363 * fixing it if necessary, but otherwise ignoring the 364 * fact that it was incorrect. 365 */ 366 return 0; 367 } 368