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