linux-kernel - Re: Possible problem in linux file posix capabilities

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Date:	Sun, 17 Feb 2008 17:20:21 -0800
From:	"Andrew G. Morgan" <morgan@...nel.org>
To:	"Serge E. Hallyn" <serue@...ibm.com>
CC:	charles.kirsch@...ernet.lu, lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Gerald Combs <gerald@...eshark.org>,
	Gilbert Ramirez <gram@...mni.rice.edu>,
	Guy Harris <guy@...m.mit.edu>
Subject: Re: Possible problem in linux file posix capabilities

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Serge E. Hallyn wrote:
| Andrew, this pretty much was bound to happen...  we need to figure out
| what our approach here should be.  My preference is still to allow
| signals when p->uid==current->uid so long as !SECURE_NOROOT.  Then as
| people start using secure_noroot process trees they at least must know
| what they're asking for.

I don't think there is anything special about root.

I've been trying to advocate that we remove the *uid == 0 part of this
check since we discussed it in November:

As I said 11/29/07 [Re: [patch 31/55] file capabilities: don't prevent
signaling	setuid root programs]:
| I actually said (11/26/07):
|> >> Serge,
|> >>
|> >> I still feel a bit uneasy about this. Looking ahead, with filesystem
|> >> capabilities, one can simulate this same situation with a setuid
|> >> 'non-root' program as follows:
|> >>
|> >> [... example of simulating the same situation with setuid-non-root
...]
|> >>
|> >> Is there a compelling reason to include the euid==0 check?

So, independent of whether SECURE_NOROOT is in effect or not, I think
this particular line should simply read:

~        if (p->uid == current->uid)
~                 return 0;

| An alternative stance is to accept these things as they come up and try
| to quickly work with the authors of such programs to work around it.  I
| suppose in a security sense that's the superior way :)  But it also
| seems likely to lead to most people choosing option 2 above and not
| bothering to fix the problem.

Cheers

Andrew
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