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
readboot(int dosfs,struct bootblock * boot)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
writefsinfo(int dosfs,struct bootblock * boot)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