Linux Forensics

Initial Information Gathering

Basic Information

First of all, it's recommended to have some USB with good known binaries and libraries on it (you can just get a ubuntu and copy the folders /bin, /sbin, /lib, and /lib64), then mount the USN, and modify the env variables to use those binaries:

export PATH=/mnt/usb/bin:/mnt/usb/sbin
export LD_LIBRARY_PATH=/mnt/usb/lib:/mnt/usb/lib64

Once you have configured the system to use good and known binaries you can start extracting some basic information:

date #Date and time (Clock my be skewed, Might be in different timezone)
uname -a #OS info
ifconfig -a || ip a #Network interfaces (promiscuosu mode?)
ps -ef #Running processes
netstat -anp #Proccess and ports
lsof -V #Open files
netstat -rn; route #Routing table
df; mount #Free space and mounted devices
free #Meam and swap space
w #Who is connected
last -Faiwx #Logins
lsmod #What is loaded
cat /etc/passwd #Unexpected data?
cat /etc/shadow #Unexpected data?
find /directory -type f -mtime -1 -print #Find modified files during the last minute in the directory

Suspicious information

While obtaining the basic information you should check for weird things like:

root processes usually run with low PIDS, so if you find a root process with a big PID you may suspect
Check registered logins of users without a shell inside /etc/passwd
Check for password hashes inside /etc/shadow for users without a shell

Memory Dump

In order to obtain the memory of the running system it's recommended to use LiME. In order to compile it you need to use the exact same kernel the victim machine is using.

Remember that you cannot install LiME or any other thing in the victim machine it will make several changes to it

So, if you have an identical version of Ubuntu you can use apt-get install lime-forensics-dkms In other cases you need to download LiME from github can compile it with correct kernel headers. In order to obtain the exact kernel headers of the victim machine, you can just copy the directory /lib/modules/<kernel version> to your machine, and then compile LiME using them:

make -C /lib/modules/<kernel version>/build M=$PWD
sudo insmod lime.ko "path=/home/sansforensics/Desktop/mem_dump.bin format=lime"

LiME supports 3 formats:

Raw (every segment concatenated together)
Padded (same as raw, but with zeroes in right bits)
Lime (recommended format with metadata

LiME can also be use to send the dump via network instead of storing it on the system using something like: path=tcp:4444

Disk Imaging

Shutting down

First of all you will need to shutdown the system. This isn't always an option as some times system will be a production server that the company cannot afford to shutdown. There are 2 ways of shutting down the system, a normal shutdown and a "plug the plug" shutdown. The first one will allow the processes to terminate as usual and the filesystem to be synchronized, but I will also allow the possible malware to destroy evidences. The "pull the plug" approach may carry some information loss (as we have already took an image of the memory not much info is going to be lost) and the malware won't have any opportunity to do anything about it. Therefore, if you suspect that there may be a malware, just execute the sync command on the system and pull the plug.

Taking an image of the disk

It's important to note that before connecting to your computer anything related to the case, you need to be sure that it's going to be mounted as read only to avoid modifying the any information.

#Create a raw copy of the disk
dd if=<subject device> of=<image file> bs=512

#Raw copy with hashes along the way (more secur s it checks hashes while it's copying the data)
dcfldd if=<subject device> of=<image file> bs=512 hash=<algorithm> hashwindow=<chunk size> hashlog=<hash file>
dcfldd if=/dev/sdc of=/media/usb/pc.image hash=sha256 hashwindow=1M hashlog=/media/usb/pc.hashes

Disk Image pre-analysis

Imaging that you receive a disk image with no more data.

#Find that it's actually a disk imageusing "file" command
file disk.img 
disk.img: Linux rev 1.0 ext4 filesystem data, UUID=59e7a736-9c90-4fab-ae35-1d6a28e5de27 (extents) (64bit) (large files) (huge files)

#Check which type of disk image it's
img_stat -t evidence.img 
raw
#You can list supported types with
img_stat -i list
Supported image format types:
        raw (Single or split raw file (dd))
        aff (Advanced Forensic Format)
        afd (AFF Multiple File)
        afm (AFF with external metadata)
        afflib (All AFFLIB image formats (including beta ones))
        ewf (Expert Witness Format (EnCase))

#Data of the image
fsstat -i raw -f ext4 disk.img 
FILE SYSTEM INFORMATION
--------------------------------------------
File System Type: Ext4
Volume Name: 
Volume ID: 162850f203fd75afab4f1e4736a7e776

Last Written at: 2020-02-06 06:22:48 (UTC)
Last Checked at: 2020-02-06 06:15:09 (UTC)

Last Mounted at: 2020-02-06 06:15:18 (UTC)
Unmounted properly
Last mounted on: /mnt/disk0

Source OS: Linux
[...]

#ls inside the image
fls -i raw -f ext4 disk.img
d/d 11: lost+found
d/d 12: Documents
d/d 8193:       folder1
d/d 8194:       folder2
V/V 65537:      $OrphanFiles

#ls inside folder
fls -i raw -f ext4 disk.img 12
r/r 16: secret.txt

#cat file inside image
icat -i raw -f ext4 disk.img 16
ThisisTheMasterSecret

Search for known Malware

Modified System Files

Some Linux systems have a feature to verify the integrity of many installed components, providing an effective way to identify unusual or out of place files. For instance, rpm -Va on Linux is designed to verify all packages that were installed using RedHat Package Manager.

#RedHat
rpm -Va
#Debian
dpkg --verify
debsums | grep -v "OK$" #apt-get install debsums

Malware/Rootkit Detectors

Read the following page to learn about tools that can be useful to find malware:

Malware Analysis

Search installed programs

Package Manager

On Debian-based systems, the /var/ lib/dpkg/status file contains details about installed packages and the /var/log/dpkg.log file records information when a package is installed. On RedHat and related Linux distributions the rpm -qa --root=/ mntpath/var/lib/rpm command will list the contents of an RPM database on a subject systems.

#Debian
cat /var/lib/dpkg/status | grep -E "Package:|Status:"
cat /var/log/dpkg.log | grep installed
#RedHat
rpm -qa --root=/ mntpath/var/lib/rpm

Other

Not all installed programs will be listed by the above commands because some applications are not available as packages for certain systems and must be installed from source. Therefore, a review of locations such as /usr/local and /opt may reveal other applications that have been compiled and installed from source code.

ls /opt /usr/local

Another good idea is to check the common folders inside $PATH for binaries not related to installed packages:

#Both lines are going to print the executables in /sbin non related to installed packages
#Debian
find /sbin/ -exec dpkg -S {} \; | grep "no path found"
#RedHat
find /sbin/ –exec rpm -qf {} \; | grep "is not"

Inspect AutoStart locations

Scheduled Tasks

cat /var/spool/cron/crontabs/*  \
/var/spool/cron/atjobs \
/var/spool/anacron \
/etc/cron* \
/etc/at* \
/etc/anacrontab \
/etc/incron.d/* \
/var/spool/incron/* \

#MacOS
ls -l /usr/lib/cron/tabs/ /Library/LaunchAgents/ /Library/LaunchDaemons/ ~/Library/LaunchAgents/

Services

It is extremely common for malware to entrench itself as a new, unauthorized service. Linux has a number of scripts that are used to start services as the computer boots. The initialization startup script /etc/inittab calls other scripts such as rc.sysinit and various startup scripts under the /etc/rc.d/ directory, or /etc/rc.boot/ in some older versions. On other versions of Linux, such as Debian, startup scripts are stored in the /etc/init.d/ directory. In addition, some common services are enabled in /etc/inetd.conf or /etc/xinetd/ depending on the version of Linux. Digital investigators should inspect each of these startup scripts for anomalous entries.

/etc/inittab
/etc/rc.d/
/etc/rc.boot/
/etc/init.d/
/etc/inetd.conf
/etc/xinetd/
/etc/systemd/system
/etc/systemd/system/multi-user.target.wants/

Kernel Modules

On Linux systems, kernel modules are commonly used as rootkit components to malware packages. Kernel modules are loaded when the system boots up based on the configuration information in the /lib/modules/'uname -r' and /etc/modprobe.d directories, and the /etc/modprobe or /etc/modprobe.conf file. These areas should be inspected for items that are related to malware.

Other AutoStart Locations

There are several configuration files that Linux uses to automatically launch an executable when a user logs into the system that may contain traces of malware.

/etc/profile.d/* , /etc/profile , /etc/bash.bashrc are executed when any user account logs in.
∼/.bashrc , ∼/.bash_profile , ~/.profile , ∼/.config/autostart are executed when the specific user logs in.
/etc/rc.local It is traditionally executed after all the normal system services are started, at the end of the process of switching to a multiuser runlevel.

Examine Logs

Look in all available log files on the compromised system for traces of malicious execution and associated activities such as creation of a new service.

Pure Logs

Logon events recorded in the system and security logs, including logons via the network, can reveal that malware or an intruder gained access to a compromised system via a given account at a specific time. Other events around the time of a malware infection can be captured in system logs, including the creation of a new service or new accounts around the time of an incident. Interesting system logons:

/var/log/syslog (debian) **or /var/log/messages** (Redhat)
- Shows general messages and info regarding the system. Basically a data log of all activity throughout the global system.
/var/log/auth.log (debian) **or /var/log/secure** (Redhat)
- Keep authentication logs for both successful or failed logins, and authentication processes. Storage depends on system type.
- cat /var/log/auth.log | grep -iE "session opened for|accepted password|new session|not in sudoers"
/var/log/boot.log: start-up messages and boot info.
/var/log/maillog or var/log/mail.log: is for mail server logs, handy for postfix, smtpd, or email-related services info running on your server.
/var/log/kern.log: keeps in Kernel logs and warning info. Kernel activity logs (e.g., dmesg, kern.log, klog) can show that a particular service crashed repeatedly, potentially indicating that an unstable trojanized version was installed.
/var/log/dmesg: a repository for device driver messages. Use dmesg to see messages in this file.
/var/log/faillog: records info on failed logins. Hence, handy for examining potential security breaches like login credential hacks and brute-force attacks.
/var/log/cron: keeps a record of Crond-related messages (cron jobs). Like when the cron daemon started a job.
/var/log/daemon.log: keeps track of running background services but doesn’t represent them graphically.
/var/log/btmp: keeps a note of all failed login attempts.
/var/log/httpd/: a directory containing error_log and access_log files of the Apache httpd daemon. Every error that httpd comes across is kept in the error_log file. Think of memory problems and other system-related errors. access_log logs all requests which come in via HTTP.
/var/log/mysqld.log or /var/log/mysql.log : MySQL log file that records every debug, failure and success message, including starting, stopping and restarting of MySQL daemon mysqld. The system decides on the directory. RedHat, CentOS, Fedora, and other RedHat-based systems use /var/log/mariadb/mariadb.log. However, Debian/Ubuntu use /var/log/mysql/error.log directory.
/var/log/xferlog: keeps FTP file transfer sessions. Includes info like file names and user-initiated FTP transfers.
/var/log/* : You should always check for unexpected logs in this directory

Linux system logs and audit subsystems may be disabled or deleted in an intrusion or malware incident. In fact, because logs on Linux systems generally contain some of the most useful information about malicious activities, intruders routinely delete them. Therefore, when examining available log files, it is important to look for gaps or out of order entries that might be an indication of deletion or tampering.

Command History

Many Linux systems are configured to maintain a command history for each user account:

~/.bash_history
~/.history
~/.sh_history
~/.*_history

Logins

Using the command last -Faiwx it's possible to get the list of users that have logged in. It's recommended to check if those logins make sense:

Any unknown user?
Any user that shouldn't have a shell has logged in?

This is important as attackers some times may copy /bin/bash inside /bin/false so users like lightdm may be able to login.

Note that you can also take a look to this information reading the logs.

Application Traces

SSH: Connections to systems made using SSH to and from a compromised system result in entries being made in files for each user account (∼/.ssh/authorized_keys and ∼/.ssh/known_keys). These entries can reveal the hostname or IP address of the remote hosts.
Gnome Desktop: User accounts may have a ∼/.recently-used.xbel file that contains information about files that were recently accessed using applications running in the Gnome desktop.
VIM: User accounts may have a ∼/.viminfo file that contains details about the use of VIM, including search string history and paths to files that were opened using vim.
Open Office: Recent files.
MySQL: User accounts may have a ∼/.mysql_history file that contains queries executed using MySQL.
Less: User accounts may have a ∼/.lesshst file that contains details about the use of less, including search string history and shell commands executed via less

USB Logs

usbrip is a small piece of software written in pure Python 3 which parses Linux log files (/var/log/syslog* or /var/log/messages* depending on the distro) for constructing USB event history tables.

It is interesting to know all the USBs that have been used and it will be more useful if you have an authorized list of USB to find "violation events" (the use of USBs that aren't inside that list).

Installation

pip3 install usbrip
usbrip ids download #Downloal USB ID database

Examples

usbrip events history #Get USB history of your curent linux machine
usbrip events history --pid 0002 --vid 0e0f --user kali #Search by pid OR vid OR user
#Search for vid and/or pid
usbrip ids download #Downlaod database
usbrip ids search --pid 0002 --vid 0e0f #Search for pid AND vid

More examples and info inside the github: https://github.com/snovvcrash/usbrip

Review User Accounts and Logon Activities

Examine the /etc/passwd, /etc/shadow and security logs for unusual names or accounts created and/or used in close proximity to known unauthorized events. Also check possible sudo brute-force attacks. Moreover, check files like /etc/sudoers and /etc/groups for unexpected privileges given to users. Finally look for accounts with no passwords or easily guessed passwords.

Examine File System

File system data structures can provide substantial amounts of information related to a malware incident, including the timing of events and the actual content of malware. Malware is increasingly being designed to thwart file system analysis. Some malware alter date-time stamps on malicious files to make it more difficult to find them with time line analysis. Other malicious code is designed to only store certain information in memory to minimize the amount of data stored in the file system. To deal with such anti-forensic techniques, it is necessary to pay careful attention to time line analysis of file system date-time stamps and to files stored in common locations where malware might be found.

Using autopsy you can see the timeline of events that may be useful to discover suspicions activity. You can also use the mactime feature from Sleuth Kit directly.
Check for unexpected scripts inside $PATH (maybe some sh or php scripts?)
Files in /dev use to be special files, you may find non-special files here related to malware.
Look for unusual or hidden files and directories, such as “.. ” (dot dot space) or “..^G ” (dot dot control-G)
setuid copies of /bin/bash on the system find / -user root -perm -04000 –print
Review date-time stamps of deleted inodes for large numbers of files being deleted around the same time, which might indicate malicious activity such as installation of a rootkit or trojanized service.
Because inodes are allocated on a next available basis, malicious files placed on the system at around the same time may be assigned consecutive inodes. Therefore, after one component of malware is located, it can be productive to inspect neighbouring inodes.
Also check directories like /bin or /sbin as the modified and/or changed time of new or modified files me be interesting.
It's interesting to see the files and folders of a directory sorted by creation date instead alphabetically to see which files/folders are more recent (last ones usually).

You can check the most recent files of a folder using ls -laR --sort=time /bin You can check the inodes of the files inside a folder using ls -lai /bin |sort -n

Note that an attacker can modify the time to make files appear legitimate, but he cannot modify the inode. If you find that a file indicates that it was created and modify at the same time of the rest of the files in the same folder, but the inode is unexpectedly bigger, then the timestamps of that file were modified.

Compare files of different filesystem versions

Find added files

git diff --no-index --diff-filter=A _openwrt1.extracted/squashfs-root/ _openwrt2.extracted/squashfs-root/

Find Modified content

git diff --no-index --diff-filter=M _openwrt1.extracted/squashfs-root/ _openwrt2.extracted/squashfs-root/ | grep -E "^\+" | grep -v "Installed-Time"

Find deleted files

git diff --no-index --diff-filter=A _openwrt1.extracted/squashfs-root/ _openwrt2.extracted/squashfs-root/

Other filters

-diff-filter=[(A|C|D|M|R|T|U|X|B)…[*]]

Select only files that are Added (A), Copied (C), Deleted (D), Modified (M), Renamed (R), have their type (i.e. regular file, symlink, submodule, …) changed (T), are Unmerged (U), are Unknown (X), or have had their pairing Broken (B). Any combination of the filter characters (including none) can be used. When * (All-or-none) is added to the combination, all paths are selected if there is any file that matches other criteria in the comparison; if there is no file that matches other criteria, nothing is selected.

Also, these upper-case letters can be downcased to exclude. E.g. --diff-filter=ad excludes added and deleted paths.

Note that not all diffs can feature all types. For instance, diffs from the index to the working tree can never have Added entries (because the set of paths included in the diff is limited by what is in the index). Similarly, copied and renamed entries cannot appear if detection for those types is disabled.

References

MBR - Master Boot Record

The MBR occupies the sector 0 of the disk (the first sector) and it's used to indicate the partitions of the disc. This sector is essential to indicate the PC what and from where a partition should be mounted. It allows up to four partitions (at most just 1 can be active/bootable). However, if you need more partitions you can use extended partitions.

Format:

Offset

Length

Item

0 (0x00)

446(0x1BE)

Boot code

446 (0x1BE)

16 (0x10)

First Partition

462 (0x1CE)

16 (0x10)

Second Partition

478 (0x1DE)

16 (0x10)

Third Partition

494 (0x1EE)

16 (0x10)

Fourth Partition

510 (0x1FE)

2 (0x2)

Signature 0x55 0xAA

Partition Record Format:

Offset

Length

Item

0 (0x00)

1 (0x01)

Active flag (0x80 = bootable)

1 (0x01)

Start head

2 (0x02)

1 (0x01)

Start sector (bits 0-5); upper bits of cylinder (6- 7)

3 (0x03)

1 (0x01)

Start cylinder lowest 8 bits

4 (0x04)

1 (0x01)

Partition type code (0x83 = Linux)

5 (0x05)

1 (0x01)

End head

6 (0x06)

1 (0x01)

End sector (bits 0-5); upper bits of cylinder (6- 7)

7 (0x07)

1 (0x01)

End cylinder lowest 8 bits

8 (0x08)

4 (0x04)

Sectors preceding partition (little endian)

12 (0x0C)

4 (0x04)

Sectors in partition

In order to mount a MBR in Linux you first need to get the start offset (you can use fdisk and the the p command)

An then use the following code

#Mount MBR in Linux
mount -o ro,loop,offset=<Bytes>
#63x512 = 32256Bytes
mount -o ro,loop,offset=32256,noatime /path/to/image.dd /media/part/

Ext - Extended Filesystem

Ext2 is the most common filesystem for not journaling partitions (partitions that don't change much) like the boot partition. Ext3/4 are journaling and are used usually for the rest partitions.

All block groups in the filesystem have the same size and are stored sequentially. This allows the kernel to easily derive the location of a block group in a disk from its integer index.

Every block group contains the following pieces of information:

A copy of the filesystem’s superblock
A copy of the block group descriptors
A data block bitmap which is used to identify the free blocks inside the group
An inode bitmap, which is used to identify the free inodes inside the group
inode table: it consists of a series of consecutive blocks, each of which contains a predefined Figure 1 Ext2 inode number of inodes. All inodes have the same size: 128 bytes. A 1,024 byte block contains 8 inodes, while a 4,096-byte block contains 32 inodes. Note that in Ext2, there is no need to store on disk a mapping between an inode number and the corresponding block number because the latter value can be derived from the block group number and the relative position inside the inode table. For example, suppose that each block group contains 4,096 inodes and that we want to know the address on disk of inode 13,021. In this case, the inode belongs to the third block group and its disk address is stored in the 733rd entry of the corresponding inode table. As you can see, the inode number is just a key used by the Ext2 routines to retrieve the proper inode descriptor on disk quickly
data blocks, containing files. Any block which does not contain any meaningful information, it is said to be free.

Ext Optional Features

Features affect where the data is located, how the data is stored in inodes and some of them might supply additional metadata for analysis, therefore features are important in Ext.

Ext has optional features that your OS may or may not support, there are 3 possibilities:

Compatible
Incompatible
Compatible Read Only: It can be mounted but not for writing

If there are incompatible features you won't be able to mount the filesystem as the OS won't know how the access the data.

Suspected attacker might have non-standard extensions

Any utility that reads the superblock will be able to indicate the features of a Ext filesystem, but you could also use file -sL /dev/sd*

Superblock

The superblock is the first 1024 bytes from the start, it's repeated in the first block of each group and contains:

Block size
Total blocks
Blocks per block group
Reserved blocks before the first block group
Total inodes
Inodes per block group
Volume name
Last write time
Last mount time
Path where the file system was last mounted
Filesystem status (clean?)

It's possible to obtain this information from an Ext filesystem file using:

fsstat -o <offsetstart> /pat/to/filesystem-file.ext
#You can get the <offsetstart> with the "p" command inside fdisk

You can also use the free gui application: https://www.disk-editor.org/index.html Or you can also use python to obtain the superblock information: https://pypi.org/project/superblock/

inodes

The inodes contain the list of blocks that contains the actual data of a file. If the file is big, and inode may contain pointers to other inodes that points to the blocks/more inodes containing the file data.

In Ext2 and Ext3 inodes are of size 128B, Ext4 currently uses 156B but allocates 256B on disk to allow a future expansion.

Inode structure:

Offset

Size

Name

DescriptionF

0x0

File Mode

File mode and type

0x2

UID

Lower 16 bits of owner ID

0x4

Size Il

Lower 32 bits of file size

0x8

Atime

Access time in seconds since epoch

0xC

Ctime

Change time in seconds since epoch

0x10

Mtime

Modify time in seconds since epoch

0x14

Dtime

Delete time in seconds since epoch

0x18

GID

Lower 16 bits of group ID

0x1A

Hlink count

Hard link count

0xC

Blocks Io

Lower 32 bits of block count

0x20

Flags

0x24

Union osd1

Linux: I version

0x28

Block[15]

15 pointes to data block

0x64

Version

File version for NFS

0x68

File ACL low

Lower 32 bits of extended attributes (ACL, etc)

0x6C

File size hi

Upper 32 bits of file size (ext4 only)

0x70

Obsolete fragment

An obsoleted fragment address

0x74

Osd 2

Second operating system dependent union

0x74

Blocks hi

Upper 16 bits of block count

0x76

File ACL hi

Upper 16 bits of extended attributes (ACL, etc.)

0x78

UID hi

Upper 16 bits of owner ID

0x7A

GID hi

Upper 16 bits of group ID

0x7C

Checksum Io

Lower 16 bits of inode checksum

"Modify" is the timestamp of the last time the file's content has been mofified. This is often called "mtime". "Change" is the timestamp of the last time the file's inode has been changed, like by changing permissions, ownership, file name, number of hard links. It's often called "ctime".

Inode structure extended (Ext4):

Offset

Size

Name

Description

0x80

Extra size

How many bytes beyond standard 128 are used

0x82

Checksum hi

Upper 16 bits of inode checksum

0x84

Ctime extra

Change time extra bits

0x88

Mtime extra

Modify time extra bits

0x8C

Atime extra

Access time extra bits

0x90

Crtime

File create time (seconds since epoch)

0x94

Crtime extra

File create time extra bits

0x98

Version hi

Upper 32 bits of version

0x9C

Unused

Reserved space for future expansions

Special inodes:

Inode

Special Purpose

No such inode, numberings starts at 1

Defective block list

Root directory

User quotas

Group quotas

Boot loader

Undelete directory

Reserved group descriptors (for resizing filesystem)

Journal

Exclude inode (for snapshots)

Replica inode

First non-reserved inode (often lost + found)

Not that the creation time only appears in Ext4.

Knowing the inode number you can easily find it's index:

Block group where an inode belongs: (Inode number - 1) / (Inodes per group)
Index inside it's group: (Inode number - 1) mod(Inodes/groups)
Offset into inode table: Inode number * (Inode size)
The "-1" is because the inode 0 is undefined (not used)

ls -ali /bin | sort -n #Get all inode numbers and sort by them
stat /bin/ls #Get the inode information of a file
istat -o <start offset> /path/to/image.ext 657103 #Get information of that inode inside the given ext file
icat -o <start offset> /path/to/image.ext 657103 #Cat the file

File Mode

Number

Description

Reg/Slink-13/Socket-14

Directory/Block Bit 13

Char Device/Block Bit 14

FIFO

Set UID

Set GID

Sticky Bit (without it, anyone with Write & exec perms on a directory can delete and rename files)

Owner Read

Owner Write

Owner Exec

Group Read

Group Write

Group Exec

Others Read

Others Write

Others Exec

The bold bits (12, 13, 14, 15) indicate the type of file the file is (a directory, socket...) only one of the options in bold may exit.

Directories

Offset

Size

Name

Description

0x0

Inode

0x4

Rec len

Record length

0x6

Name len

Name length

0x7

File type

0x00 Unknown 0x01 Regular

0x02 Director

0x03 Char device

0x04 Block device

0x05 FIFO

0x06 Socket

0x07 Sym link

0x8

Name

Name string (up to 255 characters)

In order to increase the performance, Root hash Directory blocks may be used.

Extended Attributes

Can be stored in

Extra space between inodes (256 - inode size, usually = 100)
A data block pointed to by file_acl in inode

Can be used to store anything as a users attribute if name starts with "user".

Data can ne hidden this way.

Extended Attributes Entries

Offset

Size

Name

Description

0x0

Name len

Length of attribute name

0x1

Name index

0x0 = no prefix

0x1 = user. Prefix

0x2 = system.posix_acl_access

0x3 = system.posix_acl_default

0x4 = trusted.

0x6 = security.

0x7 = system.

0x8 = system.richacl

0x2

Value offs

Offset from first inode entry or start of block

0x4

Value blocks

Disk block where value stored or zero for this block

0x8

Value size

Length of value

0xC

Hash

Hash for attribs in block or zero if in inode

0x10

Name

Attribute name w/o trailing NULL

setfattr -n 'user.secret' -v 'This is a secret' file.txt #Save a secret using extended attributes
getfattr file.txt #Get extended attribute names of a file
getdattr -n 'user.secret' file.txt #Get extended attribute called "user.secret"

Filesystem View

In order to see the contents of the file system you can use the free tool: https://www.disk-editor.org/index.html Or you can mount it in your linux using mount command.

https://piazza.com/class_profile/get_resource/il71xfllx3l16f/inz4wsb2m0w2oz#:~:text=The%20Ext2%20file%20system%20divides,lower%20average%20disk%20seek%20time.

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Last updated 3 years ago