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

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Date:	Tue, 26 Feb 2008 01:18:32 +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, Oleg Nesterov wrote:
>
> 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.

Actually, I may be wrong, sorry. If the task does setuid exec, we probably
should do these checks.

OK, please ignore 2nd and 3rd patches.

Still. The usage of security_task_kill(secid) doesn't look good, imho.
We have the similar issues with send_sigio(). In that case we use
security_file_send_sigiotask(), not security_task_kill().

Oleg.

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