xref: /freebsd/usr.sbin/fstyp/msdosfs.c (revision ec0ea6efa1ad229d75c394c1a9b9cac33af2b1d3)
1 /*-
2  * Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
3  * Copyright (c) 2006 Tobias Reifenberger
4  * Copyright (c) 2014 The FreeBSD Foundation
5  * All rights reserved.
6  *
7  * This software was developed by Edward Tomasz Napierala under sponsorship
8  * from the FreeBSD Foundation.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29  * SUCH DAMAGE.
30  */
31 
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
34 
35 #include <stdio.h>
36 #include <stdlib.h>
37 #include <string.h>
38 
39 #include "fstyp.h"
40 #include "msdosfs.h"
41 
42 #define LABEL_NO_NAME		"NO NAME    "
43 
44 int
45 fstyp_msdosfs(FILE *fp, char *label, size_t size)
46 {
47 	FAT_BSBPB *pfat_bsbpb;
48 	FAT32_BSBPB *pfat32_bsbpb;
49 	FAT_DES *pfat_entry;
50 	uint8_t *sector0, *sector;
51 	size_t copysize;
52 
53 	sector0 = NULL;
54 	sector = NULL;
55 
56 	/* Load 1st sector with boot sector and boot parameter block. */
57 	sector0 = (uint8_t *)read_buf(fp, 0, 512);
58 	if (sector0 == NULL)
59 		return (1);
60 
61 	/* Check for the FAT boot sector signature. */
62 	if (sector0[510] != 0x55 || sector0[511] != 0xaa) {
63 		goto error;
64 	}
65 
66 	/*
67 	 * Test if this is really a FAT volume and determine the FAT type.
68 	 */
69 
70 	pfat_bsbpb = (FAT_BSBPB *)sector0;
71 	pfat32_bsbpb = (FAT32_BSBPB *)sector0;
72 
73 	if (UINT16BYTES(pfat_bsbpb->BPB_FATSz16) != 0) {
74 		/*
75 		 * If the BPB_FATSz16 field is not zero and the string "FAT" is
76 		 * at the right place, this should be a FAT12 or FAT16 volume.
77 		 */
78 		if (strncmp(pfat_bsbpb->BS_FilSysType, "FAT", 3) != 0) {
79 			goto error;
80 		}
81 
82 		/* A volume with no name should have "NO NAME    " as label. */
83 		if (strncmp(pfat_bsbpb->BS_VolLab, LABEL_NO_NAME,
84 		    sizeof(pfat_bsbpb->BS_VolLab)) == 0) {
85 			goto endofchecks;
86 		}
87 		copysize = MIN(size - 1, sizeof(pfat_bsbpb->BS_VolLab));
88 		memcpy(label, pfat_bsbpb->BS_VolLab, copysize);
89 		label[copysize] = '\0';
90 	} else if (UINT32BYTES(pfat32_bsbpb->BPB_FATSz32) != 0) {
91 		uint32_t fat_FirstDataSector, fat_BytesPerSector, offset;
92 
93 		/*
94 		 * If the BPB_FATSz32 field is not zero and the string "FAT" is
95 		 * at the right place, this should be a FAT32 volume.
96 		 */
97 		if (strncmp(pfat32_bsbpb->BS_FilSysType, "FAT", 3) != 0) {
98 			goto error;
99 		}
100 
101 		/*
102 		 * If the volume label is not "NO NAME    " we're done.
103 		 */
104 		if (strncmp(pfat32_bsbpb->BS_VolLab, LABEL_NO_NAME,
105 		    sizeof(pfat32_bsbpb->BS_VolLab)) != 0) {
106 			copysize = MIN(size - 1,
107 			    sizeof(pfat32_bsbpb->BS_VolLab));
108 			memcpy(label, pfat32_bsbpb->BS_VolLab, copysize);
109 			label[copysize] = '\0';
110 			goto endofchecks;
111 		}
112 
113 		/*
114 		 * If the volume label "NO NAME    " is in the boot sector, the
115 		 * label of FAT32 volumes may be stored as a special entry in
116 		 * the root directory.
117 		 */
118 		fat_FirstDataSector =
119 		    UINT16BYTES(pfat32_bsbpb->BPB_RsvdSecCnt) +
120 		    (pfat32_bsbpb->BPB_NumFATs *
121 		     UINT32BYTES(pfat32_bsbpb->BPB_FATSz32));
122 		fat_BytesPerSector = UINT16BYTES(pfat32_bsbpb->BPB_BytsPerSec);
123 
124 		//    fat_FirstDataSector, fat_BytesPerSector);
125 
126 		for (offset = fat_BytesPerSector * fat_FirstDataSector;;
127 		    offset += fat_BytesPerSector) {
128 			sector = (uint8_t *)read_buf(fp, offset, fat_BytesPerSector);
129 			if (sector == NULL)
130 				goto error;
131 
132 			pfat_entry = (FAT_DES *)sector;
133 			do {
134 				/* No more entries available. */
135 				if (pfat_entry->DIR_Name[0] == 0) {
136 					goto endofchecks;
137 				}
138 
139 				/* Skip empty or long name entries. */
140 				if (pfat_entry->DIR_Name[0] == 0xe5 ||
141 				    (pfat_entry->DIR_Attr &
142 				     FAT_DES_ATTR_LONG_NAME) ==
143 				    FAT_DES_ATTR_LONG_NAME) {
144 					continue;
145 				}
146 
147 				/*
148 				 * The name of the entry is the volume label if
149 				 * ATTR_VOLUME_ID is set.
150 				 */
151 				if (pfat_entry->DIR_Attr &
152 				    FAT_DES_ATTR_VOLUME_ID) {
153 					copysize = MIN(size - 1,
154 					    sizeof(pfat_entry->DIR_Name));
155 					memcpy(label, pfat_entry->DIR_Name,
156 					    copysize);
157 					label[copysize] = '\0';
158 					goto endofchecks;
159 				}
160 			} while((uint8_t *)(++pfat_entry) <
161 			    (uint8_t *)(sector + fat_BytesPerSector));
162 			free(sector);
163 		}
164 	} else {
165 		goto error;
166 	}
167 
168 endofchecks:
169 	rtrim(label, size);
170 
171 	free(sector0);
172 	free(sector);
173 
174 	return (0);
175 
176 error:
177 	free(sector0);
178 	free(sector);
179 
180 	return (1);
181 }
182