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From: Paul Moore <paul@paul-moore.com>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: casey.schaufler@intel.com, James Morris <jmorris@namei.org>,
	linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
	keescook@chromium.org, john.johansen@canonical.com,
	penguin-kernel@i-love.sakura.ne.jp,
	Stephen Smalley <sds@tycho.nsa.gov>
Subject: Re: [PATCH v15 05/23] net: Prepare UDS for security module stacking
Date: Mon, 9 Mar 2020 21:02:41 -0400
Message-ID: <CAHC9VhTAk7+Zuh6vcOd=9hb-5aWY6=Rgv2aVqnSCm1q+TCHNGA@mail.gmail.com> (raw)
In-Reply-To: <50b463c1-1ff1-caad-3e4c-6e822e1c4a7a@schaufler-ca.com>

On Mon, Mar 9, 2020 at 8:13 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
> On 3/6/2020 2:14 PM, Paul Moore wrote:
> > On Fri, Feb 14, 2020 at 6:42 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
> >> Change the data used in UDS SO_PEERSEC processing from a
> >> secid to a more general struct lsmblob. Update the
> >> security_socket_getpeersec_dgram() interface to use the
> >> lsmblob. There is a small amount of scaffolding code
> >> that will come out when the security_secid_to_secctx()
> >> code is brought in line with the lsmblob.
> >>
> >> Reviewed-by: Kees Cook <keescook@chromium.org>
> >> Reviewed-by: John Johansen <john.johansen@canonical.com>
> >> Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
> >> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> >> cc: netdev@vger.kernel.org
> >> ---
> >>  include/linux/security.h |  7 +++++--
> >>  include/net/af_unix.h    |  2 +-
> >>  include/net/scm.h        |  8 +++++---
> >>  net/ipv4/ip_sockglue.c   |  8 +++++---
> >>  net/unix/af_unix.c       |  6 +++---
> >>  security/security.c      | 18 +++++++++++++++---
> >>  6 files changed, 34 insertions(+), 15 deletions(-)
> > ...
> >
> >> diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> >> index 17e10fba2152..59af08ca802f 100644
> >> --- a/include/net/af_unix.h
> >> +++ b/include/net/af_unix.h
> >> @@ -36,7 +36,7 @@ struct unix_skb_parms {
> >>         kgid_t                  gid;
> >>         struct scm_fp_list      *fp;            /* Passed files         */
> >>  #ifdef CONFIG_SECURITY_NETWORK
> >> -       u32                     secid;          /* Security ID          */
> >> +       struct lsmblob          lsmblob;        /* Security LSM data    */
> >>  #endif
> >>         u32                     consumed;
> >>  } __randomize_layout;
> > This might be a problem.  As it currently stands, the sk_buff.cb field
> > is 48 bytes; with CONFIG_SECURITY_NETWORK=n unix_skb_parms is 28 bytes
> > on a 64-bit system.  That leaves 20 bytes (room for 5 LSMs) assuming a
> > tight packing *and* that netdev doesn't swoop in and drop another few
> > fields in unix_skb_parms.
> >
> > This may work now, and you might manage to sneak this by the netdev
> > crowd, but I predict problems in the future.
>
> Do you think that making this a struct lsmblob * instead would make
> the change more likely to be accepted? It would complicate the code
> but remove the issue.

I honestly have no idea anymore when it comes to the netdev crowd.  I
can toss out a few examples, but you've been in this space long enough
to have seen the same things I have wrt to LSMs and the networking
folks.

Regardless of the implementation, I don't think you can embed the
lsmblob struct in the skb.cb; room for five LSMs is likely going to be
a limiting factor.  Once you settle on that, no matter what you do for
a reference, pointer/index/etc., the problems are all roughly the
same.  The trick is to find out what netdev will begrudgingly accept,
and for that I'm afraid you'll need to ask them directly.

-- 
paul moore
www.paul-moore.com

  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200214234203.7086-1-casey.ref@schaufler-ca.com>
2020-02-14 23:41 ` [PATCH v15 00/23] LSM: Module stacking for AppArmor Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 01/23] LSM: Infrastructure management of the sock security Casey Schaufler
2020-03-06 20:37     ` Paul Moore
2020-02-14 23:41   ` [PATCH v15 02/23] LSM: Create and manage the lsmblob data structure Casey Schaufler
2020-02-18 17:56     ` Stephen Smalley
2020-02-24 17:56     ` Mimi Zohar
2020-02-14 23:41   ` [PATCH v15 03/23] LSM: Use lsmblob in security_audit_rule_match Casey Schaufler
2020-02-24 18:26     ` Mimi Zohar
2020-02-14 23:41   ` [PATCH v15 04/23] LSM: Use lsmblob in security_kernel_act_as Casey Schaufler
2020-03-06 22:06     ` Paul Moore
2020-02-14 23:41   ` [PATCH v15 05/23] net: Prepare UDS for security module stacking Casey Schaufler
2020-03-06 22:14     ` Paul Moore
2020-03-10  0:13       ` Casey Schaufler
2020-03-10  1:02         ` Paul Moore [this message]
2020-02-14 23:41   ` [PATCH v15 06/23] Use lsmblob in security_secctx_to_secid Casey Schaufler
2020-03-07  0:58     ` Paul Moore
2020-03-10  1:13       ` Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 07/23] LSM: Use lsmblob in security_secid_to_secctx Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 08/23] LSM: Use lsmblob in security_ipc_getsecid Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 09/23] LSM: Use lsmblob in security_task_getsecid Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 10/23] LSM: Use lsmblob in security_inode_getsecid Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 11/23] LSM: Use lsmblob in security_cred_getsecid Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 12/23] IMA: Change internal interfaces to use lsmblobs Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 13/23] LSM: Specify which LSM to display Casey Schaufler
2020-03-07  1:49     ` Paul Moore
2020-02-14 23:41   ` [PATCH v15 14/23] LSM: Ensure the correct LSM context releaser Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 15/23] LSM: Use lsmcontext in security_secid_to_secctx Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 16/23] LSM: Use lsmcontext in security_inode_getsecctx Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 17/23] LSM: security_secid_to_secctx in netlink netfilter Casey Schaufler
2020-03-07  2:06     ` Paul Moore
2020-02-14 23:41   ` [PATCH v15 18/23] NET: Store LSM netlabel data in a lsmblob Casey Schaufler
2020-03-07  2:14     ` Paul Moore
2020-03-10  1:21       ` Casey Schaufler
2020-02-14 23:41   ` [PATCH v15 19/23] LSM: Verify LSM display sanity in binder Casey Schaufler
2020-02-14 23:42   ` [PATCH v15 20/23] Audit: Add subj_LSM fields when necessary Casey Schaufler
2020-02-14 23:42   ` [PATCH v15 21/23] Audit: Include object data for all security modules Casey Schaufler
2020-02-14 23:42   ` [PATCH v15 22/23] LSM: Add /proc attr entry for full LSM context Casey Schaufler
2020-02-18 18:17     ` Stephen Smalley
2020-02-14 23:42   ` [PATCH v15 23/23] AppArmor: Remove the exclusive flag Casey Schaufler
2020-02-18 18:19     ` Stephen Smalley

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