irmd: Deliver flow re-keying

Re-key each encrypted flow's batch root periodically so a long-lived
flow never exhausts or over-uses a single root. The IRMd re-runs the
OAP exchange with the peer IRMd over the flow-update relay. The
per-flow re-keying state is tracked in the registry (reg_flow).

A re-key delivers one root seed from the OAP exchange. keyrot
immediately HKDF-expands it into 128 node keys (KR_NODES_SZ = 128 × 32
B) and wipes the root. Then each of the 128 node keys is itself a root
→ HKDF-expanded into 64 (2^KEY_NODE_BITS) leaf keys, forked per
direction; each leaf key is the actual AEAD key, good for 2^20 packets
(the low counter bits are its nonce/seq). If the number of keys runs
low, a re-key will be triggered (KEY_REKEY_WATERMARK).

The rekey is signalled out of band to the application. The rbuff ACL
is generalized into a flags word, so an RB_REKEY bit rides alongside
the access RB_RD/RB_WR and FLOWDOWN/FLOWPEER bits. The RD and WR bits
are revised ditching the fcntl historical weirdness. The seed is
pulled via flow_read/flow_write, installed with crypt_rekey(). TX
holds the old epoch until the peer is observed on the new one (or a
grace deadline elapses), promoted from both the read and write paths
so a recv-mostly flow still advances.

Also fix the FLOW_ACCEPT and FLOW_ALLOC handlers, which on a key-buffer
allocation failure returned from inside the cleanup-push region: that
leaked the reply message and skipped both the stack-key scrub and the
cleanup pop.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

2 files changed, 14 insertions, 8 deletions

diff --git a/include/ouroboros/fqueue.h b/include/ouroboros/fqueue.h
index 2546c79d..322da3ea 100644
--- a/include/ouroboros/fqueue.h
+++ b/include/ouroboros/fqueue.h
@@ -34,7 +34,8 @@ enum fqtype {
         FLOW_UP      = (1 << 2),
         FLOW_ALLOC   = (1 << 3),
         FLOW_DEALLOC = (1 << 4),
-        FLOW_PEER    = (1 << 5)
+        FLOW_PEER    = (1 << 5),
+        FLOW_UPD     = (1 << 6)
 };
 
 struct flow_set;
diff --git a/include/ouroboros/ssm_rbuff.h b/include/ouroboros/ssm_rbuff.h
index 2443b63d..e77eec09 100644
--- a/include/ouroboros/ssm_rbuff.h
+++ b/include/ouroboros/ssm_rbuff.h
@@ -28,10 +28,12 @@
 
 #include <stdint.h>
 
-#define ACL_RDWR     0000
-#define ACL_RDONLY   0001
-#define ACL_FLOWDOWN 0002
-#define ACL_FLOWPEER 0004
+#define RB_RD       0001 /* read permitted  (0 = no access)        */
+#define RB_WR       0002 /* write permitted (0 = no access)        */
+#define RB_RDWR     (RB_RD | RB_WR)
+#define RB_FLOWDOWN 0004
+#define RB_FLOWPEER 0010
+#define RB_REKEY    0020 /* re-key seed parked (out-of-band signal) */
 
 struct ssm_rbuff;
 
@@ -45,10 +47,13 @@ struct ssm_rbuff * ssm_rbuff_open(pid_t pid,
 
 void               ssm_rbuff_close(struct ssm_rbuff * rb);
 
-void               ssm_rbuff_set_acl(struct ssm_rbuff * rb,
-                                     uint32_t           flags);
+void               ssm_rbuff_set_bits(struct ssm_rbuff * rb,
+                                      uint32_t           bits);
 
-uint32_t           ssm_rbuff_get_acl(struct ssm_rbuff * rb);
+void               ssm_rbuff_clr_bits(struct ssm_rbuff * rb,
+                                      uint32_t           bits);
+
+uint32_t           ssm_rbuff_get_flags(struct ssm_rbuff * rb);
 
 void               ssm_rbuff_fini(struct ssm_rbuff * rb);