linux-kernel - Re: [RFC 1/1] LSM ptags: Add tagging of processes

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Message-Id: <201611282241.FCF69778.FFMOFQLJtSVOOH@I-love.SAKURA.ne.jp>
Date:   Mon, 28 Nov 2016 22:41:53 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     jobol@...adev.net
Cc:     linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/1] LSM ptags: Add tagging of processes

Jose Bollo wrote:
> The fact is that ptags is seat behind the implementation of the special
> files in /proc/PID/attr/.. Thus, it has to return an allocated buffer.
> I'm not aware of what kind of allocation is possible to use for this
> subsystem. Is it possible to use vmalloc? I dont know.

If you replace kfree() with kvfree() in proc_pid_attr_read() in fs/proc/base.c ,
you will be able to use vmalloc(). However, proc_pid_attr_write() accepts only
PAGE_SIZE bytes from the beginning. If you want to use attributes longer than
PAGE_SIZE bytes, I think that you will need to use a different interface because
implementing I/O protocol for ptags which reads/writes PAGE_SIZE bytes chunk
at a time using /proc/PID/attr/ interface is not userspace friendly.