Linux File Permissions

Author: Dariusz Piasecki Project Type: File System Security – Permission Management
Environment: Linux (Terminal)

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📋 Project Description

As a security professional working with a research team at a large organization, my objective is to ensure that users are authorized with appropriate file and directory permissions. This project involves examining existing permissions on the file system, identifying any misconfigurations, and modifying them to comply with organizational security policies.

The analysis and changes were performed within the /tmp/projects directory using standard Linux commands (ls, chmod).

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🎯 Objectives

1. Review current file and directory permissions in the target directory
2. Identify files and directories with unauthorized access
3. Modify permissions to align with organizational security policies
4. Verify changes were applied correctly

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📁 Step 1: Review Current Permissions

The first step was to examine all files and directories, including hidden files, using the following command:

ls -la /tmp/projects

Command Breakdown:

Flag	Purpose
ls	Lists directory contents
-l	Displays detailed information (permissions, ownership, size)
-a	Includes hidden files (files starting with .)

Output:

-rw-rw----  1 root  root  0 Feb  3 09:41 .project_x.txt
drwxr-x---  2 root  root  6 Feb  3 09:41 drafts
-rw-rw-rw-  1 root  root  0 Feb  3 09:41 project_k.txt
-rw-r-----  1 root  root  0 Feb  3 09:41 project_m.txt
-rw-rw-r--  1 root  root  0 Feb  3 09:41 project_r.txt
-rw-rw-r--  1 root  root  0 Feb  3 09:41 project_t.txt

Permission String Breakdown

Using project_k.txt (-rw-rw-rw-) as an example:

Position	Characters	Meaning
1st	-	Regular file (not a directory)
2nd–4th	rw-	Owner (user): read + write
5th–7th	rw-	Group: read + write
8th–10th	rw-	Others: read + write

Initial Permission Summary

File / Directory	Type	Owner	Group	Others	Issue
drafts	Directory	rwx	r-x	---	Group has access – should be owner only
project_k.txt	File	rw-	rw-	rw-	⚠️ Others have write access
project_m.txt	File	rw-	r--	---	✅ No issues
project_r.txt	File	rw-	rw-	r--	✅ Others have read only
project_t.txt	File	rw-	rw-	r--	✅ Others have read only
.project_x.txt	Hidden file	rw-	rw-	---	⚠️ Group and owner have write access

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🔧 Step 2: Remove Write Access for Others

Security Policy: No file should allow write access for "others."

After reviewing the initial permissions, only project_k.txt had write access for others (-rw-rw-rw-). The files project_r.txt and project_t.txt already had read-only permissions for others (-rw-rw-r--), so no changes were required for them.

Command Applied:

chmod o-w /tmp/projects/project_k.txt

Command Breakdown:

Component	Meaning
chmod	Change file permissions
o-w	Remove (-) write (w) permission for others (o)
/tmp/projects/project_k.txt	Target file path

Verification:

ls -l /tmp/projects

Result:

File	Permissions Before	Permissions After	Change Applied
project_k.txt	-rw-rw-rw-	-rw-rw-r--	✅ Write removed for others
project_m.txt	-rw-r-----	-rw-r-----	— No change needed
project_r.txt	-rw-rw-r--	-rw-rw-r--	— Already compliant
project_t.txt	-rw-rw-r--	-rw-rw-r--	— Already compliant

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🔧 Step 3: Modify Permissions on a Hidden File

Security Policy: The hidden file .project_x.txt must allow read access for the owner and group only. No write access for anyone.

Command Applied:

chmod u=r,g=r,o= /tmp/projects/.project_x.txt

Command Breakdown:

Component	Meaning
u=r	Set owner (user) permissions to read only
g=r	Set group permissions to read only
o=	Remove all permissions for others

Verification:

ls -la /tmp/projects/.project_x.txt

Result:

File	Permissions Before	Permissions After	Change Applied
.project_x.txt	-rw-rw----	-r--r-----	✅ Write removed for owner and group

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🔧 Step 4: Restrict Directory Access

Security Policy: The drafts directory should only be accessible by its owner (researcher2).

The original permissions (drwxr-x---) allowed the research group to read and navigate the directory. To restrict access to the owner only, the permissions were changed using the numeric (octal) method.

Command Applied:

chmod 700 /tmp/projects/drafts

Command Breakdown:

Value	Who	Permissions Granted
7	Owner (user)	Read + Write + Execute (rwx)
0	Group	No permissions (---)
0	Others	No permissions (---)

Verification:

ls -ld /tmp/projects/drafts

Result:

Directory	Permissions Before	Permissions After	Change Applied
drafts	drwxr-x---	drwx------	✅ Access restricted to owner only

Note: The research group previously had read and execute access to the drafts directory. Removing this access means other team members can no longer browse or read files inside drafts. This change should be confirmed with the team manager before deployment.

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📊 Final Permissions Overview

After all changes were applied, the final state of the directory is as follows:

drwx------  2 root  root  6 Feb  3 09:41 drafts
-rw-rw-r--  1 root  root  0 Feb  3 09:41 project_k.txt
-rw-r-----  1 root  root  0 Feb  3 09:41 project_m.txt
-rw-rw-r--  1 root  root  0 Feb  3 09:41 project_r.txt
-rw-rw-r--  1 root  root  0 Feb  3 09:41 project_t.txt
-r--r-----  1 root  root  0 Feb  3 09:41 .project_x.txt

Complete Change Summary

File / Directory	Before	After	Action Taken
drafts	drwxr-x---	drwx------	Removed group access
project_k.txt	-rw-rw-rw-	-rw-rw-r--	Removed write for others
project_m.txt	-rw-r-----	-rw-r-----	No change – already compliant
project_r.txt	-rw-rw-r--	-rw-rw-r--	No change – already compliant
project_t.txt	-rw-rw-r--	-rw-rw-r--	No change – already compliant
.project_x.txt	-rw-rw----	-r--r-----	Removed write for owner and group

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🛠️ Commands Reference

Command	Purpose	Used In
ls -la	List all files including hidden, with details	Step 1
ls -l	List files with permission details	Steps 2, 3
ls -ld	List directory details (not contents)	Step 4
chmod o-w	Remove write permission for others	Step 2
chmod u=r,g=r,o=	Set exact permissions for user, group, others	Step 3
chmod 700	Set permissions using octal notation	Step 4

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🎯 Skills Demonstrated

Skill Category	Specific Skills
Linux Administration	File system navigation, permission management
Security Hardening	Identifying and fixing unauthorized access
chmod Usage	Symbolic (o-w, u=r) and octal (700) notation
Access Control	Least privilege principle, user/group/others model
Documentation	Step-by-step technical reporting with verification

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📧 Contact

Dariusz Piasecki
📧 Email: dariusz.piasecki.sec@gmail.com
🔗 LinkedIn: linkedin.com/in/dariusz-piasecki
🐙 GitHub: github.com/Dariusz-Piasecki

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This project demonstrates practical Linux file permission management as part of a cybersecurity portfolio, focusing on access control and security hardening.