Linux Forensics by Philip Polstra

Linux Forensics by Philip Polstra

Author:Philip Polstra [Polstra, Philip]
Language: eng
Format: azw3, epub
Publisher: Pentester Academy
Published: 2015-09-30T04:00:00+00:00


Metadata Csum

Checksums are used on metadata items



The filesystem supports replicas



Should only be mounted as read-only

When the Sparse Superblock feature is in use, the superblock is only found in block group 0 or in block groups that are a power of 3, 5, or 7. If there is at least one file greater than 2 gigabytes on the filesystem, the Large File feature flag will be set. The Huge File feature flag indicates at least one huge file is present. Huge files have their sizes specified in clusters (the size of which is stored in the superblock) instead of data blocks.

The Btree Directory feature allows large directories to be stored in binary-trees. This is not common. Another feature related to large directories is Directory Nlink. When the Directory Nlink flag is set, subdirectories are not limited to 32,768 entries as in previous versions of ext3.

The GDT Checksum feature allows checksums to be stored in the group descriptor tables. The Extra Isize feature flag indicates that large inodes are present on the filesystem. If a filesystem snapshot is present, the Has Snapshot flag will be set. Disk quota use is indicated by the Quota feature flag.

The Big Alloc feature is useful if most of the files on the filesystem are huge. When this is in use, file extents (discussed later in this chapter) and other filesystem structures use multi-block clusters for units. The Metadata Checksum flag indicates that checksums are stored for the metadata items in inodes, etc. If a filesystem supports replicas, the Replica flag will be set. A filesystem with the Read Only flag set should only be mounted as read-only. This flag can be set to prevent others from modifying the filesystem’s contents.

Only two features in the read-only compatible set affect the filesystem layout: Sparse Super Blocks and Extra Isize. Sparse super blocks affect which block groups have superblock backups. Like 64-bit mode, the Extra Isize feature affects the layout indirectly by changing the inode size.


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