linux-kernel - Re: [PATCH 2/3] kill_pid_info_as_uid: don't use security_task

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Message-ID: <20080225200328.GA83@tv-sign.ru>
Date:	Mon, 25 Feb 2008 23:03:28 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	David Quigley <dpquigl@...ho.nsa.gov>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Eric Paris <eparis@...hat.com>,
	Harald Welte <laforge@...monks.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"Serge E. Hallyn" <serue@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] kill_pid_info_as_uid: don't use security_task_kill()

On 02/25, Stephen Smalley wrote:
> 
> On Mon, 2008-02-25 at 20:42 +0300, Oleg Nesterov wrote:
> > kill_pid_info_as_uid() is solely used by drivers/usb/core/. The original
> > "[PATCH] Fix signal sending in usbdevio on async URB completion" commit
> > 46113830a18847cff8da73005e57bc49c2f95a56 was right, but nowadays we use
> > struct pid and this solves most of the addressed problems.
> > 
> > It would be nice to use kill_pid_info() instead, but we can't because USB
> > uses .si_code = SI_ASYNCIO which fools SI_FROMUSER() and thus security checks.
> > 
> > I think we should omit the permission checks completely, the task which does
> > ioctl(USBDEVFS_SUBMITURB) explicitly asks to send the signal to it, we should
> > not deny the signal even if the task changes its credentials in any way.
> 
> If we are applying checks based on uid/gid to protect suid/sgid
> programs, then we ought to also invoke the LSM hook to allow protection
> of other credential-changing transformations, like SELinux context
> transitions.  You either remove all checking or none, please.

Yes, you are right. I'd like to remove all uid/euid checks. This patch doesn't
do this because

	- perhaps it will be possible to kill this helper

	- if we remove these checks, we should do some subsequent cleanups
	  in drivers/usb/core/, while this series is all about LSM hooks.

I am going to do this later.

> And if all, what's the rationale?

I think it is not good that LSM has some special (and unneeded!) hacks for USB.
Please also look at the next patch.


Do you agree?

Oleg.

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