From: Stephen Smalley <sds@tycho.nsa.gov>
To: Sebastien Buisson <sbuisson.ddn@gmail.com>
Cc: linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, selinux@tycho.nsa.gov,
serge@hallyn.com, james.l.morris@oracle.com,
Eric Paris <eparis@parisplace.org>,
Paul Moore <paul@paul-moore.com>,
Daniel Jurgens <danielj@mellanox.com>,
Sebastien Buisson <sbuisson@ddn.com>
Subject: Re: [PATCH 2/3] selinux: add checksum to policydb
Date: Fri, 28 Apr 2017 12:38:07 -0400 [thread overview]
Message-ID: <1493397487.6177.10.camel@tycho.nsa.gov> (raw)
In-Reply-To: <CAPkE-bWd0ArebM+8Vm5ZCQd90avZQ5sPSAR_2P5Y1brK5wKwJQ@mail.gmail.com>
On Fri, 2017-04-28 at 18:08 +0200, Sebastien Buisson wrote:
> 2017-04-28 17:50 GMT+02:00 Stephen Smalley <sds@tycho.nsa.gov>:
> > You seem to be conflating kernel policy with userspace policy.
> > security_load_policy() is provided with the kernel policy image,
> > which
> > is the result of linking the kernel-relevant portions of all policy
> > modules together. A hash of that image will change if you insert a
> > policy module that affects the kernel policy in any way. But a
> > change
> > that only affects userspace policy isn't ever going to be reflected
> > in
> > the kernel. It doesn't matter where or when you compute your
> > checksum
> > within the kernel; it isn't ever going to reflect those userspace
> > policy changes.
>
> Here is the content of the module is used for my tests:
>
> #============= user_t ==============
> allow user_t mnt_t:dir { write add_name };
> allow user_t mnt_t:file { write create };
>
> After loading the .pp corresponding to it, I can see that with the
> method of computing the checksum on the (data, len) pair on entry to
> security_load_policy(), the checksum does not change. However, when
> using the (data, len) pair got from
> security_read_policy(), the checksum changes. And when I remove the
> module, the checksum is back to its previous value.
> So this is what makes me think there is a difference. Am I missing
> something?
Policy is loaded via security_load_policy(), so the policy image has to
go through it in the first place to be loaded (ignoring kernel exploits
or direct /dev/mem access). You couldn't have loaded the modified
policy with your new rules without the modified policy getting
processed by security_load_policy(). So I'm assuming there is a bug in
your code or your testing.
next prev parent reply other threads:[~2017-04-28 16:34 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-26 15:02 [PATCH 1/3] selinux: Implement LSM notification system Sebastien Buisson
2017-04-26 15:02 ` [PATCH 2/3] selinux: add checksum to policydb Sebastien Buisson
2017-04-26 18:30 ` Stephen Smalley
2017-04-27 8:41 ` Sebastien Buisson
2017-04-27 15:18 ` Stephen Smalley
2017-04-27 17:12 ` Sebastien Buisson
2017-04-27 18:47 ` Stephen Smalley
2017-04-28 15:16 ` Sebastien Buisson
2017-04-28 15:50 ` Stephen Smalley
2017-04-28 16:08 ` Sebastien Buisson
2017-04-28 16:38 ` Stephen Smalley [this message]
2017-04-26 15:02 ` [PATCH 3/3] selinux: expose policy SHA256 checksum via selinuxfs Sebastien Buisson
2017-04-26 18:31 ` Stephen Smalley
2017-04-27 1:08 ` James Morris
2017-04-26 15:38 ` [PATCH 1/3] selinux: Implement LSM notification system Casey Schaufler
2017-04-26 15:48 ` Daniel Jurgens
2017-04-26 15:57 ` Sebastien Buisson
2017-04-26 16:11 ` Casey Schaufler
2017-04-26 17:36 ` Stephen Smalley
2017-04-26 17:47 ` Casey Schaufler
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