LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Casey Schaufler <casey@schaufler-ca.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>,
	Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>,
	Matthew Garrett <mjg59@google.com>,
	linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] kexec: call LSM hook for kexec_load syscall
Date: Thu, 3 May 2018 09:05:22 -0700	[thread overview]
Message-ID: <6203b1e4-70c3-6d0e-60e0-56c6e8f72ec9@schaufler-ca.com> (raw)
In-Reply-To: <87h8nospo5.fsf@xmission.com>

On 5/3/2018 8:51 AM, Eric W. Biederman wrote:
> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
>
>> On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote:
>>> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
>>>
>>>> Allow LSMs and IMA to differentiate between the kexec_load and
>>>> kexec_file_load syscalls by adding an "unnecessary" call to
>>>> security_kernel_read_file() in kexec_load.  This would be similar to the
>>>> existing init_module syscall calling security_kernel_read_file().
>>> Given the reasonable desire to load a policy that ensures everything
>>> has a signature I don't have fundamental objections.
>>>
>>> security_kernel_read_file as a hook seems an odd choice.  At the very
>>> least it has a bad name because there is no file reading going on here.
>>>
>>> I am concerned that I don't see CONFIG_KEXEC_VERIFY_SIG being tested
>>> anywhere.  Which means I could have a kernel compiled without that and I
>>> would be allowed to use kexec_file_load without signature checking.
>>> While kexec_load would be denied.
>>>
>>> Am I missing something here?
>> The kexec_file_load() calls kernel_read_file_from_fd(), which in turn
>> calls security_kernel_read_file().  So kexec_file_load and kexec_load
>> syscall would be using the same method for enforcing signature
>> verification.
> Having looked at your patches and the kernel a little more I think
> this should be a separate security hook that does not take a file
> parameter.
>
> Right now every other security module assumes !file is init_module.
> So I think this change has the potential to confuse other security
> modules, with the result of unintended policy being applied.
>
> So just for good security module hygeine I think this needs a dedicated
> kexec_load security hook.

I would rather see the existing modules updated than a new
hook added. Too many hooks spoil the broth. Two hooks with
trivial differences just add to the clutter and make it harder
for non-lsm developers to figure out what to use in their
code. 

  reply	other threads:[~2018-05-03 16:05 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-12 22:41 [PATCH 0/3] kexec: limit " Mimi Zohar
2018-04-12 22:41 ` [PATCH 1/3] ima: based on the "secure_boot" policy limit syscalls Mimi Zohar
2018-04-12 22:41 ` [PATCH 2/3] kexec: call LSM hook for kexec_load syscall Mimi Zohar
2018-05-02 14:45   ` Eric W. Biederman
2018-05-02 15:45     ` Mimi Zohar
2018-05-03 15:51       ` Eric W. Biederman
2018-05-03 16:05         ` Casey Schaufler [this message]
2018-05-03 16:42           ` Eric W. Biederman
2018-05-03 21:06             ` Mimi Zohar
2018-05-03 21:36               ` Eric W. Biederman
2018-04-12 22:41 ` [PATCH 3/3] ima: based on policy require signed kexec kernel images Mimi Zohar
2018-05-03 20:13 ` [PATCH 0/3] kexec: limit kexec_load syscall Eric W. Biederman
2018-05-03 20:39   ` Matthew Garrett
2018-05-03 21:58     ` Eric W. Biederman
2018-05-03 22:51       ` Matthew Garrett
2018-05-03 21:31   ` Mimi Zohar
2018-05-03 21:38     ` Eric W. Biederman
2018-05-03 21:57       ` Mimi Zohar
2018-05-03 23:03         ` Eric W. Biederman
2018-05-04  2:29           ` Mimi Zohar
2018-05-11  1:36 Mimi Zohar
2018-05-11  1:36 ` [PATCH 2/3] kexec: call LSM hook for " Mimi Zohar

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=6203b1e4-70c3-6d0e-60e0-56c6e8f72ec9@schaufler-ca.com \
    --to=casey@schaufler-ca.com \
    --cc=dhowells@redhat.com \
    --cc=ebiederm@xmission.com \
    --cc=kexec@lists.infradead.org \
    --cc=linux-integrity@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=mjg59@google.com \
    --cc=zohar@linux.vnet.ibm.com \
    --subject='Re: [PATCH 2/3] kexec: call LSM hook for kexec_load syscall' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).