Harden Sigil: sigil/viewcodes.py

sigil/viewcodes.py

@@ -53,17 +53,32 @@ def normalise(code: str) -> str:
 
 def issue_code(
     store: Store,
-    agent: str,
+    session_token: str,
     scopes: Optional[List[str]] = None,
     code_ttl: int = DEFAULT_CODE_TTL,
     view_ttl: int = DEFAULT_VIEW_TTL,
+    limit: Optional[int] = None,
+    window: Optional[int] = None,
 ) -> dict:
-    """Mint a one-time view code on behalf of an agent.
+    """Mint a one-time view code for the agent that owns `session_token`.
 
-    Called only from an agent session. The agent is recorded as the grantor so
-    the audit trail shows a human was let in by that agent, not that the agent
-    itself was present.
+    The caller must present a live agent session. There is deliberately no
+    `agent` argument: the agent is derived from the session, so a code can
+    never be minted for some other agent, and a route that forgets to
+    authenticate fails closed instead of minting a session for whoever asked.
+
+    The code lives code_ttl seconds; the session it mints lives view_ttl
+    seconds from the moment it is redeemed.
+
+    The agent is recorded as the grantor so the audit trail shows a human was
+    let in by that agent, not that the agent itself was present.
     """
+    principal = sessions.resolve(store, session_token)
+    agent = sessions.assert_may_act_as_agent(principal)
+
+    if not store.allow(f"code_issue:{agent}", limit=limit, window=window):
+        raise errors.RateLimited(f"too many view codes for {agent}")
+
     agent_row = store.get_agent(agent)
     if agent_row is None:
         raise errors.UnknownAgent(f"{agent} is not enrolled")
@@ -87,7 +102,7 @@ def issue_code(
         agent,
         granted,
         redeem_expires_at=now + code_ttl,
-        session_expires_at=now + view_ttl,
+        view_ttl=view_ttl,
     )
     store.record(
         "view_code.issued",
@@ -98,7 +113,6 @@ def issue_code(
             "code_prefix": code[:5],
             "scopes": granted,
             "redeem_expires_at": now + code_ttl,
-            "session_expires_at": now + view_ttl,
         },
     )
     return {
@@ -108,12 +122,17 @@ def issue_code(
         "code_ttl": code_ttl,
         "view_ttl": view_ttl,
         "redeem_expires_at": now + code_ttl,
-        "session_expires_at": now + view_ttl,
+        "view_ttl": view_ttl,
     }
 
 
 def redeem_code(store: Store, code: str) -> dict:
     """Trade a one-time code for a human_via_agent session."""
+    # Rate-limit before the lookup so a guessing attacker cannot use response
+    # differences to probe for valid codes for free.
+    if not store.allow("code_redeem_fail"):
+        raise errors.RateLimited("too many redemption attempts")
+
     digest = _hash_code(normalise(code))
     row = store.get_code(digest)
     if row is None:
@@ -124,15 +143,6 @@ def redeem_code(store: Store, code: str) -> dict:
 
     agent = row["agent"]
 
-    if row["used_at"] is not None:
-        store.record(
-            "view_code.redeem_refused",
-            actor=agent,
-            subject=f"{agent}'s human",
-            detail={"reason": "already used"},
-        )
-        raise errors.CodeUsed("that code has already been used")
-
     if time.time() >= row["redeem_expires_at"]:
         store.record(
             "view_code.redeem_refused",
@@ -142,20 +152,31 @@ def redeem_code(store: Store, code: str) -> dict:
         )
         raise errors.CodeExpired("that code has expired")
 
-    # Consume before issuing, so a race cannot mint two sessions.
-    store.mark_code_used(digest)
+    # Claim the code before issuing anything. Compare-and-set, so a code cannot
+    # mint two sessions under a race, and an expired or replayed code is refused
+    # before any session exists.
+    if not store.claim_code(digest):
+        store.record(
+            "view_code.redeem_refused",
+            actor=agent,
+            subject=f"{agent}'s human",
+            detail={"reason": "already used or claimed"},
+        )
+        raise errors.CodeUsed("that code has already been used")
+
     store.record(
         "view_code.redeemed", actor=agent, subject=f"{agent}'s human", detail={}
     )
 
     import json as _json
 
-    remaining = max(0, row["session_expires_at"] - int(time.time()))
+    # The session window starts here, at redemption, not at issue. Waiting for a
+    # code must not eat into the hour the human was given.
     return sessions.issue_view_session(
         store,
         agent,
         scopes=_json.loads(row["scopes"]),
-        ttl=remaining,
+        ttl=row["view_ttl"],
         granted_by=agent,
     )
 
@@ -163,8 +184,8 @@ def redeem_code(store: Store, code: str) -> dict:
 def sweep(store: Store) -> int:
     """Report how many codes and sessions have lapsed. Housekeeping aid."""
     now = int(time.time())
-    codes = [r for r in store.conn.execute("SELECT * FROM codes").fetchall()
-             if r["used_at"] is None and now >= r["redeem_expires_at"]]
+    codes = [r for r in store.lapsed_codes()
+             if now >= r["redeem_expires_at"]]
     tokens = [r for r in store.sessions() if r["revoked_at"] is None
               and now >= r["expires_at"]]
     return len(codes) + len(tokens)