On 9/4/2020 1:08 PM, Paul Moore wrote:

On Wed, Aug 26, 2020 at 11:07 AM Casey Schaufler [off-list ref] wrote:

quoted

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@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(-)

...

quoted

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.

Stephen had concerns about the lifecycle management involved. He also
pointed out that I had taken a cowards way out when allocations failed.
That could result in unexpected behavior when an allocation failed.
Fixing that would have required a major re-write of the currently simple
UDS attribute code, which I suspect would be as hard a sell to netdev as
expanding the secid to a lsmblob. I also thought I'd gotten netdev on the
CC: for this patch, but it looks like I missed it.

I did start on the UDS attribute re-do, and discovered that I was going
to have to introduce new failure paths, and that it might not be possible
to maintain compatibility for all cases because of the new possibilities
of failure.