On Mon, Mar 9, 2020 at 8:13 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
> On 3/6/2020 2:14 PM, Paul Moore wrote:
> > On Fri, Feb 14, 2020 at 6:42 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> >> Reviewed-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
> >> Acked-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
> >> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> >> cc: netdev@xxxxxxxxxxxxxxx
> >> ---
> >> 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
