CODEWITHSUNDEEP
security
Tai Kwangi Chicken
Tai Kwangi Chicken

Reputation: 623

What Really Protects File Priveleges?

In Windows for instance, and all operating systems, file priveleges exist that "prevent" a file from being written to if that rule is set.

This is hard to describe but please listen. People coding in a C language obviously would use some form of framework to easily modify a file. Using the built-in .Net framework, Microsoft obviously would put prevention into their classes checking file permissions before writing to a file. Since file permissions are stored via software and not hardware, what really prevents a file from being tampered with?

Let's hop over to Assembly. Suppose I create an Assembly program that directly accesses hard drive data and changes the bytes of a file. How could file permissions possibly prevent me from doing this? I guess what I am trying to ask is how a file permission really stays secure if the compiled program does not check for file permissions before writing to a file?

Upvotes: 1

Views: 44

Answers (1)

Mike Samuel
Mike Samuel

Reputation: 120526

Suppose I create an Assembly program that directly accesses hard drive data and changes the bytes of a file. How could file permissions possibly prevent me from doing this?

If you write in assembly, your assembly is still run in a CPU mode that prevents direct access to memory and devices.

CPU modes … place restrictions on the type and scope of operations that can be performed by certain processes being run by the CPU. This design allows the operating system to run with more privileges than application software.

Your code still needs to issue system calls to get the OS to interact with memory not owned by your process and devices.

a system call is how a program requests a service from an operating system's kernel. This may include hardware related services (e.g. accessing the hard disk), creating and executing new processes, and communicating with integral kernel services (like scheduling).

The OS maintains security by monopolizing the ability to switch CPU modes and by crafting system calls so that they are safe for user-land code to initiate.

Upvotes: 6

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