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 $");
32 static const char rcsid[] =
33 "$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
47 int
readboot(int dosfs,struct bootblock * boot)48 readboot(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
338 int
writefsinfo(int dosfs,struct bootblock * boot)339 writefsinfo(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