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>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/lib/frct.c b/src/lib/frct.c
index 3077df65..c055433d 100644
--- a/src/lib/frct.c
+++ b/src/lib/frct.c
@@ -878,10 +878,10 @@ static void frct_mark_flow_down(struct frcti * frcti)
         struct flow * f = frcti_to_flow(frcti);
 
         if (f->rx_rb != NULL)
-                ssm_rbuff_set_acl(f->rx_rb, ACL_FLOWDOWN);
+                ssm_rbuff_set_bits(f->rx_rb, RB_FLOWDOWN);
 
         if (f->tx_rb != NULL)
-                ssm_rbuff_set_acl(f->tx_rb, ACL_FLOWDOWN);
+                ssm_rbuff_set_bits(f->tx_rb, RB_FLOWDOWN);
 }
 
 __attribute__((cold))
@@ -890,7 +890,7 @@ static void frct_mark_peer_dead(struct frcti * frcti)
         struct flow * f = frcti_to_flow(frcti);
 
         if (f->rx_rb != NULL)
-                ssm_rbuff_set_acl(f->rx_rb, ACL_FLOWPEER);
+                ssm_rbuff_set_bits(f->rx_rb, RB_FLOWPEER);
 
         if (proc.fqset != NULL)
                 ssm_flow_set_notify(proc.fqset, f->info.id, FLOW_PEER);