Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

On Wed, 19 Dec 2007 21:11:11 +0900
Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:

Hello.

Radoslaw Szkodzinski (AstralStorm) wrote:
Actually, who needs to create device nodes? Just prohibit everyone from
creating them, except "installer" and "udev" personality.
This means removing CAP_MKNOD on a global scale.

What happens if the root tampers udev's configuration file?
The udev will create inappropriate (i.e. filename with unexpected attributes)
device nodes, won't it?

Yes. But root doesn't need access to these files, at least not usually.
Create a separate user for editing config files - much lower
probability of breakage. Remove almost all capabilities from root and
profit.

After all, revoking CAP_MKNOD is not enough for guaranteeing
filename and its attributes.

This filesystem is designed to guarantee filename and its attributes,
but this filesystem has additional access control capability.
You can forbid mknod/unlink /dev/null if you want nobody to do so.
You can forbid chmod/chown /dev/null if you want nobody to do so.

You can forbid all operations on /dev (except udev) with an ACL.
So, what is the need for this filesystem?

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