Present	Absence	of	
Linux	Filesystem	Security
Philip	Derbeko
January,	2018
About	Me	(philip@ensilo.com)
Present	Absence
A	character	who	does	not	appear	for	
much	of,	if	not	all	the	plot,	but	whose	
presence	is	nevertheless	felt.	More	
accurately,	the	absence	of	the	
character	is	most	significant.
Recap	of	FS	Security
Recap	of	FS	Security
Recap	of	FS	Security
Recap	of	FS	Security
Recap	of	FS	Security
Recap	of	FS	Security
Recap	of	FS	Security
1. Read/Write/Execute
2. Inheritance
3. Only	“Allow”	permissions
Recap	of	FS	Security
Recap	of	FS	Security
Privacy	vs.	Security
The	“Root”	of	the	problem
Permanent	link	to	this	comic:	https://xkcd.com/149/
Capabilities	Anyone?
Capabilities	Anyone?
LSM	to	the	rescue	???
Issues:
- Not	mandatory
- Single	active	module
- Kernel	compilation
- Limited	Hooks
3	Security	Gaps
1.Context	of	operations
2.Weird	Operations
3.Destructive	Operations
Context	of	operations
Do	you	really	know	what	is	going	on?
Do	you	really	know	what	is	going	on?
Context	of	Operations
Weird	Operations
Weird	Operations
Weird	Operations
Weird	Operations
Destructive	Operations
Destructive	Operations
Destructive	Operations
KillDisk –
encryption	loop
Destructive	Operations
Encoder	–
encryption	loop
Destructive	Operations
Destructive	Operations	– ShieldFS assumptions/findings
1. #	of	folder	listing	operations
2. #	of	read	files
3. #	of	written	files
4. #	of	renamed	or	moved	files
5. #	of	accessed	files
6. Average	entropy	of	file-write	operations
Solution	?
contact@enSilo.com www.ensilo.com company/enSilo @enSiloSec
Thank	You
Weird	Operations

Present Absence of Linux Filesystem Security