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From: (Eric W. Biederman)
To: James Morris <>
Cc: Mimi Zohar <>,,,, David Howells <>,
	"Luis R . Rodriguez" <>,, Andres Rodriguez <>,
	Greg Kroah-Hartman <>,
	Ard Biesheuvel <>,
	Kees Cook <>,
	Casey Schaufler <>
Subject: Re: [PATCH v3 1/7] security: rename security_kernel_read_file() hook
Date: Tue, 29 May 2018 16:10:30 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <> (James Morris's message of "Wed, 30 May 2018 06:32:16 +1000 (AEST)")

James Morris <> writes:

> On Fri, 25 May 2018, Eric W. Biederman wrote:
>> James Morris <> writes:
>> > On Thu, 24 May 2018, Eric W. Biederman wrote:
>> >
>> >> Below is where I suggest you start on sorting out these security hooks.
>> >> - Adding a security_kernel_arg to catch when you want to allow/deny the
>> >>   use of an argument to a syscall.  What security_kernel_file_read and
>> >>   security_kernel_file_post_read have been abused for.
>> >
>> > NAK. This abstraction is too semantically weak.
>> >
>> > LSM hooks need to map to stronger semantics so we can reason about what 
>> > the hook and the policy is supposed to be mediating.
>> I will take that as an extremely weak nack as all I did was expose the
>> existing code and what the code is currently doing.  I don't see how you
>> can NAK what is already being merged and used.
> It's a strong NAK.

We are either not understading each other or you have just strong NAK'd
part of the existing LSM api.  Not my proposal.

> LSM is a logical API, it provides an abstraction layer for security 
> policies to mediate kernel security behaviors.

The way it deals with firmware blobs and module loading is not logical.
It is some random pass a NULL pointer into some other security hook.

> Adding an argument to a syscall is not a security behavior.
> Loading a firmware file is.

It is a firmware blob not a file.  Perhaps the blob is stored as a file
on-disk, perhaps it is not.

The similar case with kexec never stores all of the data in a file.

Why module_init (which does not take a file) is calling a file based lsm
hook is also bizarre.

Perhaps that means all 3 of these cases should have their own void
security hooks.  Perhaps it means something else.  I just know the name
on the security hook, how it is getting called, and how it is getting
used simply do not agree.


  reply	other threads:[~2018-05-29 21:10 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-24 11:09 [PATCH v3 0/7] kexec/firmware: support system wide policy requiring signatures Mimi Zohar
2018-05-24 11:09 ` [PATCH v3 1/7] security: rename security_kernel_read_file() hook Mimi Zohar
2018-05-24 20:49   ` Eric W. Biederman
2018-05-24 23:29     ` Mimi Zohar
2018-05-25 12:22     ` Mimi Zohar
2018-05-25 15:41     ` James Morris
2018-05-25 19:51       ` Eric W. Biederman
2018-05-29 20:32         ` James Morris
2018-05-29 21:10           ` Eric W. Biederman [this message]
2018-05-24 11:09 ` [PATCH v3 2/7] kexec: add call to LSM hook in original kexec_load syscall Mimi Zohar
2018-05-24 20:50   ` Eric W. Biederman
2018-05-24 11:09 ` [PATCH v3 3/7] ima: based on policy require signed kexec kernel images Mimi Zohar
2018-05-24 11:09 ` [PATCH v3 4/7] firmware: add call to LSM hook before firmware sysfs fallback Mimi Zohar
2018-05-24 11:09 ` [PATCH v3 5/7] ima: based on policy require signed firmware (sysfs fallback) Mimi Zohar
2018-05-24 11:09 ` [PATCH v3 6/7] ima: add build time policy Mimi Zohar
2018-05-24 11:09 ` [RFC PATCH v3 7/7] ima: based on policy prevent loading firmware (pre-allocated buffer) Mimi Zohar

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