1 /*
2  * Copyright (C) 1995, 1997 Wolfgang Solfrank
3  * Copyright (c) 1995 Martin Husemann
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17  * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24  */
25 
26 
27 #include <stdlib.h>
28 #include <string.h>
29 #include <stdio.h>
30 #include <unistd.h>
31 
32 #include "ext.h"
33 
34 int
readboot(int dosfs,struct bootblock * boot)35 readboot(int dosfs, struct bootblock *boot)
36 {
37 	u_char block[DOSBOOTBLOCKSIZE];
38 	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
39 	u_char backup[DOSBOOTBLOCKSIZE];
40 	int ret = FSOK;
41 	int i;
42 
43 	if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
44 		perr("could not read boot block");
45 		return FSFATAL;
46 	}
47 
48 	if (block[510] != 0x55 || block[511] != 0xaa) {
49 		pfatal("Invalid signature in boot block: %02x%02x",
50 		    block[511], block[510]);
51 		return FSFATAL;
52 	}
53 
54 	memset(boot, 0, sizeof *boot);
55 	boot->ValidFat = -1;
56 
57 	/* decode bios parameter block */
58 	boot->bpbBytesPerSec = block[11] + (block[12] << 8);
59 	boot->bpbSecPerClust = block[13];
60 	boot->bpbResSectors = block[14] + (block[15] << 8);
61 	boot->bpbFATs = block[16];
62 	boot->bpbRootDirEnts = block[17] + (block[18] << 8);
63 	boot->bpbSectors = block[19] + (block[20] << 8);
64 	boot->bpbMedia = block[21];
65 	boot->bpbFATsmall = block[22] + (block[23] << 8);
66 	boot->SecPerTrack = block[24] + (block[25] << 8);
67 	boot->bpbHeads = block[26] + (block[27] << 8);
68 	boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
69 	    (block[30] << 16) + (block[31] << 24);
70 	boot->bpbHugeSectors = block[32] + (block[33] << 8) +
71 	    (block[34] << 16) + (block[35] << 24);
72 
73 	boot->FATsecs = boot->bpbFATsmall;
74 
75 	if (!boot->bpbRootDirEnts)
76 		boot->flags |= FAT32;
77 	if (boot->flags & FAT32) {
78 		boot->FATsecs = block[36] + (block[37] << 8)
79 				+ (block[38] << 16) + (block[39] << 24);
80 		if (block[40] & 0x80)
81 			boot->ValidFat = block[40] & 0x0f;
82 
83 		/* check version number: */
84 		if (block[42] || block[43]) {
85 			/* Correct?				XXX */
86 			pfatal("Unknown file system version: %x.%x",
87 			       block[43], block[42]);
88 			return FSFATAL;
89 		}
90 		boot->bpbRootClust = block[44] + (block[45] << 8)
91 			       + (block[46] << 16) + (block[47] << 24);
92 		boot->bpbFSInfo = block[48] + (block[49] << 8);
93 		boot->bpbBackup = block[50] + (block[51] << 8);
94 
95 		if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
96 		    SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
97 		    || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
98 			perr("could not read fsinfo block");
99 			return FSFATAL;
100 		}
101 		if (memcmp(fsinfo, "RRaA", 4)
102 		    || memcmp(fsinfo + 0x1e4, "rrAa", 4)
103 		    || fsinfo[0x1fc]
104 		    || fsinfo[0x1fd]
105 		    || fsinfo[0x1fe] != 0x55
106 		    || fsinfo[0x1ff] != 0xaa
107 		    || fsinfo[0x3fc]
108 		    || fsinfo[0x3fd]
109 		    || fsinfo[0x3fe] != 0x55
110 		    || fsinfo[0x3ff] != 0xaa) {
111 			pwarn("Invalid signature in fsinfo block\n");
112 			if (ask(0, "Fix")) {
113 				memcpy(fsinfo, "RRaA", 4);
114 				memcpy(fsinfo + 0x1e4, "rrAa", 4);
115 				fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
116 				fsinfo[0x1fe] = 0x55;
117 				fsinfo[0x1ff] = 0xaa;
118 				fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
119 				fsinfo[0x3fe] = 0x55;
120 				fsinfo[0x3ff] = 0xaa;
121 				if (lseek(dosfs, boot->bpbFSInfo *
122 				    boot->bpbBytesPerSec, SEEK_SET)
123 				    != boot->bpbFSInfo * boot->bpbBytesPerSec
124 				    || write(dosfs, fsinfo, sizeof fsinfo)
125 				    != sizeof fsinfo) {
126 					perr("Unable to write bpbFSInfo");
127 					return FSFATAL;
128 				}
129 				ret = FSBOOTMOD;
130 			} else
131 				boot->bpbFSInfo = 0;
132 		}
133 		if (boot->bpbFSInfo) {
134 			boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
135 				       + (fsinfo[0x1ea] << 16)
136 				       + (fsinfo[0x1eb] << 24);
137 			boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
138 				       + (fsinfo[0x1ee] << 16)
139 				       + (fsinfo[0x1ef] << 24);
140 		}
141 
142 		if (lseek(dosfs, boot->bpbBackup * boot->bpbBytesPerSec,
143 		    SEEK_SET)
144 		    != boot->bpbBackup * boot->bpbBytesPerSec
145 		    || read(dosfs, backup, sizeof backup) != sizeof  backup) {
146 			perr("could not read backup bootblock");
147 			return FSFATAL;
148 		}
149 		backup[65] = block[65];				/* XXX */
150 		if (memcmp(block + 11, backup + 11, 79)) {
151 			/*
152 			 * XXX We require a reference that explains
153 			 * that these bytes need to match, or should
154 			 * drop the check.  gdt@NetBSD has observed
155 			 * filesystems that work fine under Windows XP
156 			 * and NetBSD that do not match, so the
157 			 * requirement is suspect.  For now, just
158 			 * print out useful information and continue.
159 			 */
160 			pfatal("backup (block %d) mismatch with primary bootblock:\n",
161 			        boot->bpbBackup);
162 			for (i = 11; i < 11 + 90; i++) {
163 				if (block[i] != backup[i])
164 					pfatal("\ti=%d\tprimary 0x%02x\tbackup 0x%02x\n",
165 					       i, block[i], backup[i]);
166 			}
167 		}
168 		/* Check backup bpbFSInfo?					XXX */
169 	}
170 
171 	boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
172 	    boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
173 	    boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
174 	    CLUST_FIRST * boot->bpbSecPerClust;
175 
176 	if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0) {
177 		pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
178 		return FSFATAL;
179 	}
180 	if (boot->bpbSecPerClust == 0) {
181 		pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
182 		return FSFATAL;
183 	}
184 	if (boot->bpbSectors) {
185 		boot->bpbHugeSectors = 0;
186 		boot->NumSectors = boot->bpbSectors;
187 	} else
188 		boot->NumSectors = boot->bpbHugeSectors;
189 	boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) /
190 	    boot->bpbSecPerClust;
191 
192 	if (boot->flags&FAT32)
193 		boot->ClustMask = CLUST32_MASK;
194 	else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK))
195 		boot->ClustMask = CLUST12_MASK;
196 	else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK))
197 		boot->ClustMask = CLUST16_MASK;
198 	else {
199 		pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
200 		       boot->NumClusters);
201 		return FSFATAL;
202 	}
203 
204 	switch (boot->ClustMask) {
205 	case CLUST32_MASK:
206 		boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4;
207 		break;
208 	case CLUST16_MASK:
209 		boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2;
210 		break;
211 	default:
212 		boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3;
213 		break;
214 	}
215 
216 	if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) {
217 		pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
218 		       boot->NumClusters, boot->FATsecs);
219 		return FSFATAL;
220 	}
221 	boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust;
222 
223 	boot->NumFiles = 1;
224 	boot->NumFree = 0;
225 
226 	// @localmod begin
227 	// The BSD FAT driver follows the FAT specification of the "dirty bit"
228 	// exactly. The Linux FAT driver, however, marks a bit in the boot sector as
229 	// "dirty", which is outside the typical FAT specification. For maximum
230 	// compatibility, this modification allows fsck to detect (and clean) the
231 	// unspecified Linux dirty bit.
232 	int dirtybyte = boot->flags&FAT32 ? 0x41 : 0x25;
233 	if (block[dirtybyte] & 0x01) {
234 		if (ask(1, "MARK BOOT BLOCK CLEAN") == 0) {
235 			pwarn("\n***** BOOT BLOCK IS LEFT MARKED AS DIRTY *****\n");
236 			return FSERROR;
237 		}
238 		pwarn("MARKING BOOT BLOCK CLEAN\n");
239 		block[dirtybyte] &= ~0x01;
240 		if (lseek(dosfs, 0, SEEK_SET) != 0
241 			|| write(dosfs, block, sizeof block) != sizeof block) {
242 			perr("could not write boot block");
243 			return FSFATAL;
244 		}
245 	}
246 	// @localmod end
247 
248 	return ret;
249 }
250 
251 int
writefsinfo(int dosfs,struct bootblock * boot)252 writefsinfo(int dosfs, struct bootblock *boot)
253 {
254 	u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
255 
256 	if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
257 	    != boot->bpbFSInfo * boot->bpbBytesPerSec
258 	    || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
259 		perr("could not read fsinfo block");
260 		return FSFATAL;
261 	}
262 	fsinfo[0x1e8] = (u_char)boot->FSFree;
263 	fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
264 	fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
265 	fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
266 	fsinfo[0x1ec] = (u_char)boot->FSNext;
267 	fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
268 	fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
269 	fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
270 	if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
271 	    != boot->bpbFSInfo * boot->bpbBytesPerSec
272 	    || write(dosfs, fsinfo, sizeof fsinfo)
273 	    != sizeof fsinfo) {
274 		perr("Unable to write bpbFSInfo");
275 		return FSFATAL;
276 	}
277 	/*
278 	 * Technically, we should return FSBOOTMOD here.
279 	 *
280 	 * However, since Win95 OSR2 (the first M$ OS that has
281 	 * support for FAT32) doesn't maintain the FSINFO block
282 	 * correctly, it has to be fixed pretty often.
283 	 *
284 	 * Therefor, we handle the FSINFO block only informally,
285 	 * fixing it if necessary, but otherwise ignoring the
286 	 * fact that it was incorrect.
287 	 */
288 	return 0;
289 }
290