.NODE

UFS2 Superblock

The UFS 2 superblock stores the same basic information as the UFS1 version, but it has removed many of the unused fields and is a little simpler. It has many of the same fields but has replaced the essential fields that were only 32 bits with 64 bit versions. It is typically located in sector 128, and the version that is used by FreeBSD and NetBSD has the fields shown in Table 17.3.

Table 17.3. Data structure for the UFS2 superblock.

Byte Range

Description

Essential

07

Unused

No

811

Offset to backup superblock in cylinder group relative to a "base"

Yes

1215

Offset to group descriptor in cylinder group relative to a "base"

Yes

1619

Offset to inode table in cylinder group relative to a "base"

Yes

2023

Offset to first data block in cylinder group relative to a "base"

No

2443

Unused

No

4447

Number of cylinder groups in file system

Yes

4851

Size of a block in bytes

Yes

5255

Size of a fragment in bytes

Yes

5659

Size of a block in fragments

No

6063

Minimum % of free blocks

No

6471

Unused

No

7275

Mask used to calculate the address for a block

No

7679

Mask used to calculate the address for a fragment

No

8083

Shift used to calculate the byte address for a block

No

8487

Shift used to calculate the byte address for a fragment

No

8891

Maximum number of contiguous blocks to allocate

No

9295

Maximum number of blocks per cylinder group

No

9699

Number of bits to convert between a block address and a fragment address

No

100103

Number of bits to convert between a fragment address and a sector address

No

104107

Size of superblock

No

108115

Unused

No

116119

Number of indirect addresses per fragment

No

120123

Number of inodes per block in inode table

No

124127

Unused

No

128131

Optimization technique

No

132143

Unused

No

144151

File System Id

No

152155

Unused

No

156159

Size of cylinder group summary area in bytes

No

160163

Size of cylinder group descriptor in bytes

No

164183

Unused

No

184187

Inodes per cylinder group

Yes

188191

Fragments per cylinder group

Yes

192207

Unused

No

208208

Super block modified flag

No

209209

FS was clean when it was mounted

No

210210

Mounted read only flag (set to 1 if read only)

No

211211

Unused

No

212679

Last mount point

No

680711

Volume name

No

712719

System UID

No

720723

Unused

No

724727

Last cylinder group searched

No

728999

Unused

No

10001007

Location of superblock

No

10081015

Number of directories

No

10161023

Number of free blocks

No

10241031

Number of free inodes

No

10321039

Number of free fragments

No

10401047

Number of free clusters

No

10481071

Unused

No

10721079

Last written time

No

10801087

Number of fragments in file system

Yes

10881095

Number of fragments that can store file data

No

10961103

Fragment address of cylinder group summary area

No

11041111

Blocks in process of being freed

No

11121115

Inodes in process of being freed

No

11161195

Array inode addresses for snap inodes

No

11961199

Expected average file size

No

12001203

Expected number of files per directory

No

12041311

Unused

No

13121315

Flags (see Table 17.2)

No

1316 1319

Size of cluster summary array in group descriptors

No

13201323

Maximum length of internal symbolic link

Yes

13241327

Format of inodes

Yes

13281335

Maximum file size

No

13361343

Mask used to calculate the offset in a block for an address

No

13441351

Mask used to calculate the offset in a fragment for an address

No

13521355

File system state

No

13561371

Unused

No

13721375

Signature value (0x19540119)

Yes

You might notice that fields have moved around. The only changes that could be of interest are that the mount point is shorter and there is now a volume label field. The flags field is four bytes instead of only one, but the same flag values given in Table 17.2 are used. Also note that the magic value is different, which is how we can differentiate between UFS1 and UFS2.

Here are the contents of a UFS2 file system from a FreeBSD 5 system:


# dd if=freebsd5.dd skip=128 count=4 | xxd

0000000: 0000 0000 0000 0000 2800 0000 3000 0000 ........(...0...

0000016: 3800 0000 d800 0000 0000 0000 0000 0000 8...............

0000032: 0000 0000 0000 0000 0000 0000 0400 0000 ................

0000048: 0040 0000 0008 0000 0800 0000 0800 0000 .@..............

0000064: 0000 0000 0000 0000 00c0 ffff 00f8 ffff ................

0000080: 0e00 0000 0b00 0000 0800 0000 0008 0000 ................

0000096: 0300 0000 0200 0000 0008 0000 0000 0000 ................

0000112: 0000 0000 0008 0000 4000 0000 0000 0000 ........@.......

0000128: 0000 0000 0000 0000 0000 0000 0000 0000 ................

0000144: adb2 0f41 fd01 4a17 0000 0000 0008 0000 ...A..J.........

0000160: 0008 0000 0000 0000 0000 0000 0000 0000 ................

0000176: 0000 0000 0000 0000 0005 0000 b813 0000 ................

0000192: 0000 0000 0000 0000 0000 0000 0000 0000 ................

0000208: 0000 0080 2f6d 6e74 0000 0000 0000 0000 ..../mnt........

[REMOVED]

0000672: 0000 0000 0000 0000 5546 5332 0000 0000 ........UFS2....

[REMOVED]

0000832: 0000 0000 0000 0000 1038 66c3 0030 66c3 .........8f..0f.

0000848: 0038 66c3 0000 0000 0000 0000 0040 0000 .8f..........@..

[REMOVED]

0000992: 0000 0000 0000 0000 0000 0100 0000 0000 ................

0001008: 0400 0000 0000 0000 f308 0000 0000 0000 ................

0001024: e213 0000 0000 0000 1800 0000 0000 0000 ................

[REMOVED]

0001072: bdb4 0f41 0000 0000 c04e 0000 0000 0000 ...A.....N......

0001088: d74b 0000 0000 0000 d800 0000 0000 0000 .K..............

[REMOVED]

0001184: 0000 0000 0000 0000 0000 0000 0040 0000 .............@..

0001200: 4000 0000 0000 0000 0000 0000 0000 0000 @...............

[REMOVED]

0001312: 0000 0000 0800 0000 7800 0000 0000 0000 ........x.......

0001328: ffff 0202 1080 0000 ff3f 0000 0000 0000 .........?......

0001344: ff07 0000 0000 0000 0000 0000 0000 0000 ................

0001360: 0000 0000 0000 0000 0000 0000 1901 5419 ..............T.

We see in bytes 8 to 11, 12 to 15, and 16 to 19 that the superblock is located 40 fragments (0x28) from the start of each cylinder group, the group descriptor is 48 fragments (0x30) from the start, and the inode table is 56 fragments (0x38) from the start. Bytes 44 to 47 show that there are four cylinder groups.

The size of a block is given in bytes 48 to 51, and we see that it is 16,384 bytes (0x4000), and the size of each fragment is in bytes 52 to 55, which is 2,048 bytes (0x0800). Bytes 184 to 187 show that there are 1,280 (0x0500) inodes per cylinder group, and bytes 188 to 191 show that there are 5,048 (0x13b8) fragments per group. The total number of fragments is given in bytes 1080 to 1087, and this small file system has only 20,160.

Here is the relevant output from running fsstat on the UFS2 image:


# fsstat f freebsd freebsd5.dd

FILE SYSTEM INFORMATION

--------------------------------------------

File System Type: UFS 2

Last Written: Tue Aug 3 10:52:29 2004

Last Mount Point: /mnt

Volume Name: UFS2

System UID: 0



METADATA INFORMATION

--------------------------------------------

Inode Range: 0 - 5119

Root Directory: 2

Num of Avail Inodes: 5090

Num of Directories: 4



CONTENT INFORMATION

--------------------------------------------

Fragment Range: 0 - 20159

Block Size: 16384

Fragment Size: 2048

Num of Avail Full Blocks: 2291

Num of Avail Fragments: 24

[REMOVED]


Part I: Foundations

Digital Investigation Foundations

Computer Foundations

Hard Disk Data Acquisition

Part II: Volume Analysis

Volume Analysis

PC-based Partitions

Server-based Partitions

Multiple Disk Volumes

Part III: File System Analysis

File System Analysis

FAT Concepts and Analysis

FAT Data Structures

NTFS Concepts

NTFS Analysis

NTFS Data Structures

Ext2 and Ext3 Concepts and Analysis

Ext2 and Ext3 Data Structures

UFS1 and UFS2 Concepts and Analysis

UFS1 and UFS2 Data Structures

Summary

Bibliography

Bibliography

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File System Forensic Analysis
File System Forensic Analysis
ISBN: 0321268172
EAN: 2147483647
Year: 2006
Pages: 184
Authors: Brian Carrier
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