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From: Richard Haines <richard_c_haines@btinternet.com>
To: Paul Moore <paul@paul-moore.com>, David Howells <dhowells@redhat.com>
Cc: keyrings@vger.kernel.org, selinux@vger.kernel.org,
	linux-security-module@vger.kernel.org
Subject: Re: Problem with 9ba09998baa9 ("selinux: Implement the watch_key security hook") in linux-next
Date: Fri, 17 Apr 2020 17:32:28 +0100
Message-ID: <56808ee47c8b6e184fd013b90072c6fb07ef84f2.camel@btinternet.com> (raw)
In-Reply-To: <CAHC9VhT95GJKNTMvTtmZL35UOoVwbGH-eDWZyELb5oZ5rQU+Tw@mail.gmail.com>

On Fri, 2020-04-17 at 11:48 -0400, Paul Moore wrote:
> I just notice that the "selinux: Implement the watch_key security
> hook" patch made it's way into linux-next via 9ba09998baa9:
> 
>   commit 9ba09998baa995518d94c9a32e6329b28ccb9045
>   Author: David Howells <dhowells@redhat.com>
>   Date:   Tue Jan 14 17:07:13 2020 +0000
> 
>    selinux: Implement the watch_key security hook
> 
>    Implement the watch_key security hook to make sure that a key
> grants the
>    caller View permission in order to set a watch on a key.
> 
>    For the moment, the watch_devices security hook is left
> unimplemented as
>    it's not obvious what the object should be since the queue is
> global and
>    didn't previously exist.
> 
>    Signed-off-by: David Howells <dhowells@redhat.com>
>    Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
> 
> I'm reasonably confident that this code hasn't been tested as I
> expect
> it would fail, or at the very least behave in unintended ways.  The
> problem is the selinux_watch_key(...) function, shown below:

I built an selinx-testsuite test for this last year and it worked fine
then. I'll send the test as an RFC patch as its been some time since I
ran it. David also has a test in kernel
samples/watch_queue/watch_test.c

> 
> +static int selinux_watch_key(struct key *key)
> +{
> +       struct key_security_struct *ksec = key->security;
> +       u32 sid = current_sid();
> +
> +       return avc_has_perm(&selinux_state,
> +                           sid, ksec->sid, SECCLASS_KEY,
> KEY_NEED_VIEW, NULL);
> +}
> 
> ... in particular it is the fifth argument to avc_has_perm(),
> "KEY_NEED_VIEW" which is a problem.  KEY_NEED_VIEW is not a SELinux

True, however by magic the KEY_NEED_* perms match with the bits defined
in classmap.h. I did some work on this during the 'keys' saga, see
various emails in list like [1]

[1] 
https://lore.kernel.org/selinux/20200220181031.156674-2-richard_c_haines@btinternet.com/

> permission and would likely result in odd behavior when passed to
> avc_has_perm().  Given that the keyring permission to SELinux object
> class permission is variable depending on the key_perms policy
> capability, it probably makes the most sense to pull the permission
> mapping in selinux_key_permission() out into a separate function,
> e.g.
> key_perm_to_av(...) (see the other XXX_to_av() functions in
> security/selinux/hooks.c), and then use this newly created mapping
> function in both selinux_key_permission() and
> selinux_watch_key().  Or
> you could just duplicate the KEY_NEED_VIEW mapping code in both
> functions, but I would advise against that.
> 


  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-17 15:48 Paul Moore
2020-04-17 16:32 ` Richard Haines [this message]
2020-04-17 16:59   ` Paul Moore
2020-04-21 12:29 ` David Howells
2020-04-22 19:20   ` Paul Moore
2020-04-22 21:09     ` Paul Moore
2020-04-24 23:43   ` David Howells
2020-04-26 20:53     ` Paul Moore
2020-04-27 14:12     ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms David Howells
2020-04-27 14:36       ` Stephen Smalley
2020-04-27 15:24         ` Paul Moore
2020-04-27 17:02       ` Stephen Smalley
2020-04-27 22:17         ` Paul Moore
2020-04-28 12:54 ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms [v2] David Howells
2020-04-28 14:32   ` Stephen Smalley
2020-04-28 15:57   ` David Howells
2020-04-28 16:19     ` Stephen Smalley
2020-05-01 16:37       ` Paul Moore
2020-05-12 22:33       ` [PATCH] keys: Make the KEY_NEED_* perms an enum rather than a mask David Howells
2020-05-13  1:04         ` Paul Moore
2020-05-13 12:58         ` Stephen Smalley
2020-05-13 15:25         ` Casey Schaufler
2020-05-13 23:13         ` David Howells
2020-05-14 12:08           ` Stephen Smalley
2020-05-14 14:45             ` Stephen Smalley
2020-05-13 23:16         ` David Howells
2020-05-13 23:25         ` David Howells
2020-05-14 11:00         ` Jarkko Sakkinen
2020-05-14 16:58         ` [PATCH] keys: Move permissions checking decisions into the checking code David Howells
2020-05-14 17:06           ` Casey Schaufler
2020-05-15 15:06           ` Stephen Smalley
2020-05-15 16:45           ` David Howells
2020-05-15 18:55             ` Stephen Smalley
2020-05-15 19:10               ` Casey Schaufler
2020-05-15 22:27             ` David Howells

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