[PATCH v20 05/23] net: Prepare UDS for security module stacking

[Paul Moore]

On Wed, Aug 26, 2020 at 11:07 AM Casey Schaufler <casey at 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.
>
> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
> ---
>  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 f42fdddecd41..a86da0cb5ec1 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    */

As mentioned in a previous revision, I remain concerned that this is
going to become a problem due to the size limit on unix_skb_parms.  I
would need to redo the math to be certain, but if I recall correctly
this would limit us to five LSMs assuming both that we don't need to
grow the per-LSM size of lsmblob *and* the netdev folks don't decide
to add more fields to the unix_skb_parms.

I lost track of that earlier discussion so I'm not sure where it ended
up, but if there is a viable alternative it might be a good idea to
pursue it.

-- 
paul moore
www.paul-moore.com