From: Andrew Morgan <morgan@kernel.org>
To: casey@schaufler-ca.com
Cc: "Serge E. Hallyn" <serue@us.ibm.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
Chris Wright <chrisw@sous-sol.org>,
Andrew Morton <akpm@linux-foundation.org>,
Stephen Smalley <sds@tycho.nsa.gov>,
James Morris <jmorris@namei.org>,
linux-security-module@vger.kernel.org,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: implement-file-posix-capabilities.patch
Date: Thu, 28 Jun 2007 22:30:27 -0700 [thread overview]
Message-ID: <468498F3.5040001@kernel.org> (raw)
In-Reply-To: <325190.92239.qm@web36610.mail.mud.yahoo.com>
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Casey Schaufler wrote:
>> Would there be a difference between that and setting either fI or fP
>> (depending on your intent) to those caps, and setting fE=1 in Andrew's
>> scheme?
>
> Arg, you're making me think. The POSIX group went through this,
> let me see if I can reconstruct the logic.
>
> The main issue is one if there being a possible case where you
> have a capability ignorant program that you want to exec with
> a different fP and fE. On first glance it seems that since the
> program is capability ignorant it can't matter. But what if your
> capability ignorant program exec's a capability aware program
> to perform a helper function? You may well want the first program
> to have a capability that it does not use in fP (but not fE)
> to pass along to the helper program. True, you could probably
I'm not sure I've quite flogged this horse to death yet.. :-)
In my other reply, I quoted the rules. Here they are again:
pI' = pI
pP' = (X & fP) | (pI & fI)
pE' = pP' & fE
If program A exec()utes helper program B, then the only capabilities
(p*') that B can get from A are a subset of A's pI set.
If A doesn't know about capabilities, then nothing about the fE value
associated with the A program file can alter A's pI set and thus affect
B. That is, nothing about the fE or fP value used to exec()ute A gets
propagated through a subsequent exec() to B.
So far as I can see, to achieve the helper program support you are
describing, the value of pI that program A (and thus program B) inherits
will have to contain the relevant capabilities, and B will have to have
a sufficient fI value to pick them up...
Incidentally, this is also where my request that we require (pP' >= fP)
be true comes in. If a helper program (which may also be a legacy
program) is used in a way that it is configured (via fP) to have powers
that are denied to it (via X=cap_bset etc.,) then it should simply not
be permitted to run (-EPERM). It should not have the opportunity to
silently confuse itself (as was the case with sendmail when we tried to
emulate setuid-0 behavior with capabilities a few years back).
> come up with a way to set the capabilities on the helper program
> to account for this use, but there may be design and security
> constraints that make doing so complicated.
I've not seen anything yet to make be believe there is a case for a
non-single bit fE value... Its a little ironic that I read all of the
rationale I've been espousing in POSIX drafts - so far as I'm aware the
only detail I'm mixing in there is the (pP' >= fP), -EPERM, thing.
If you or anyone can cite some counter examples, please do!
Cheers
Andrew
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next prev parent reply other threads:[~2007-06-29 5:30 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20070611123714.GA2063@sergelap.austin.ibm.com>
[not found] ` <878322.98602.qm@web36606.mail.mud.yahoo.com>
[not found] ` <afff21250706110926l244ddc28i44289cb08a6721e2@mail.gmail.com>
[not found] ` <20070617135239.GA17689@sergelap>
[not found] ` <4676007F.7060503@kernel.org>
[not found] ` <20070618044017.GW3723@sequoia.sous-sol.org>
[not found] ` <20070620171037.GA28670@sergelap.ibm.com>
[not found] ` <20070620174613.GF3723@sequoia.sous-sol.org>
2007-06-21 16:00 ` implement-file-posix-capabilities.patch Serge E. Hallyn
2007-06-23 8:13 ` implement-file-posix-capabilities.patch Andrew Morgan
2007-06-24 15:51 ` implement-file-posix-capabilities.patch Serge E. Hallyn
2007-06-24 16:18 ` implement-file-posix-capabilities.patch James Morris
2007-06-24 20:58 ` [PATCH][RFC] security: Convert LSM into a static interface James Morris
2007-06-24 22:09 ` Chris Wright
2007-06-24 22:37 ` James Morris
2007-06-25 1:38 ` Chris Wright
2007-06-24 23:40 ` Casey Schaufler
2007-06-25 1:39 ` Chris Wright
2007-06-25 3:37 ` Casey Schaufler
2007-06-25 3:57 ` Chris Wright
2007-06-25 13:02 ` Casey Schaufler
2007-06-25 14:24 ` Roberto De Ioris
2007-06-25 4:33 ` [PATCH try #2] " James Morris
2007-06-25 4:48 ` Petr Vandrovec
2007-06-25 4:58 ` James Morris
2007-06-25 16:59 ` Stephen Smalley
2007-06-25 23:56 ` [PATCH try #3] " James Morris
2007-06-25 20:37 ` [PATCH try #2] " Andreas Gruenbacher
2007-06-25 21:14 ` James Morris
2007-06-26 3:57 ` Serge E. Hallyn
2007-06-26 13:15 ` Adrian Bunk
2007-06-26 14:06 ` Serge E. Hallyn
2007-06-26 14:59 ` Adrian Bunk
2007-06-26 15:53 ` Serge E. Hallyn
2007-06-26 18:52 ` Adrian Bunk
2007-06-26 18:18 ` Greg KH
2007-06-26 18:40 ` Serge E. Hallyn
2007-06-26 4:09 ` Kyle Moffett
2007-06-26 4:25 ` Kyle Moffett
2007-06-26 13:47 ` Serge E. Hallyn
2007-06-27 0:07 ` Kyle Moffett
2007-06-27 0:57 ` Crispin Cowan
2007-06-27 1:22 ` Kyle Moffett
2007-06-27 4:24 ` Chris Wright
2007-06-27 13:41 ` Serge E. Hallyn
2007-06-27 14:36 ` James Morris
2007-06-27 17:21 ` Serge E. Hallyn
2007-06-27 18:51 ` Serge E. Hallyn
2007-06-27 19:28 ` James Morris
2007-06-28 2:48 ` Serge E. Hallyn
2007-06-25 3:57 ` [PATCH][RFC] " Serge E. Hallyn
2007-06-25 4:10 ` Chris Wright
2007-06-25 4:54 ` Serge E. Hallyn
2007-06-25 13:50 ` Casey Schaufler
2007-06-25 13:54 ` James Morris
2007-06-25 14:32 ` Serge E. Hallyn
2007-06-25 15:08 ` Casey Schaufler
2007-06-27 5:00 ` implement-file-posix-capabilities.patch Andrew Morgan
2007-06-27 13:16 ` implement-file-posix-capabilities.patch Serge E. Hallyn
2007-06-28 6:19 ` implement-file-posix-capabilities.patch Andrew Morgan
2007-06-28 13:36 ` implement-file-posix-capabilities.patch Serge E. Hallyn
2007-06-28 15:14 ` implement-file-posix-capabilities.patch Casey Schaufler
2007-06-28 15:38 ` implement-file-posix-capabilities.patch Serge E. Hallyn
2007-06-28 15:56 ` implement-file-posix-capabilities.patch Casey Schaufler
2007-06-29 5:30 ` Andrew Morgan [this message]
2007-06-29 13:24 ` implement-file-posix-capabilities.patch Serge E. Hallyn
2007-06-29 14:46 ` implement-file-posix-capabilities.patch Casey Schaufler
2007-06-28 15:50 ` implement-file-posix-capabilities.patch Andrew Morgan
2007-07-02 14:38 ` implement-file-posix-capabilities.patch Serge E. Hallyn
2007-07-04 21:29 ` implement-file-posix-capabilities.patch Andrew Morgan
2007-07-04 23:00 ` implement-file-posix-capabilities.patch Casey Schaufler
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