---
id: "bug-1476"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "controller"
severity: "crash"
timestamp: "2026-07-26T04:44:00Z"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 2
files: ["src/controller/config_repl.c (load_primary_config ~line 656-666 free_ClusterConfig/free(myconf->cluster_config) call site; config_activate_committed ~line 360; handle_repl_config_push ~line 1280); lib/controller.capnp.c (decode_ClusterConfig_ptr ~line 17074 calloc site", "decode_Resource_list ~line 4057 crash site)"]
tags: ["config_repl.c", "load_primary_config", "config_activate_committed", "handle_repl_config_push", "heap-use-after-free", "decode_Resource_list", "controller.capnp.c", "concurrency-race", "config-upgrade-snapshot", "task-8.9", "live-soak-finding", "bug-1474-verification-run", "new-crash", "needs-owner", "possibly-related-to-bug-1474-fix-angle-a-duplicate-reconnects", "mylock"]
related: ["bug-976", "bug-981", "bug-1474", "bug-1475"]
legacy: true
---

# bug-1476: Live config-upgrade-snapshot task 8.9 re-verification soak (run-ha-soak.sh…

## Description
Live config-upgrade-snapshot task 8.9 re-verification soak (run-ha-soak.sh --config-upgrade-wal-trim, run to confirm bug-1474's repl.c fix), deploy /home/claude/tmp/xce-ha-waltrim3: ctrl-3 ABORTed via AddressSanitizer heap-use-after-free during the round's live config-upgrade submission, well before TARGET(ctrl-1) was ever restarted. The round's own bug-1474 WAL-trim assertions (floor segment preserved, below-floor segments trimmed, active segment present) all PASSED cleanly before this crash was noticed -- ctrl-3's death was only discovered because it, combined with a second unrelated issue (bug-1475), prevented the round's final '3-of-3 reconvergence' assertion from ever succeeding.

## Environment
_Not recorded (migrated from buglog.json)._

## Reproduction
_Not recorded (migrated from buglog.json)._

## Root cause
AddressSanitizer heap-use-after-free, WRITE of size 8, in decode_Resource_list (lib/controller.capnp.c:4057), thread T5. Full ASAN trace (ctrl-3.stderr):
WRITE by T5: decode_Resource_list <- decode_ClusterConfig <- decode_ClusterConfig_ptr <- load_cluster_config_from_file (config_repl.c:606) <- load_primary_config (config_repl.c:664) <- config_activate_committed (config_repl.c:360) <- handle_repl_config_push (config_repl.c:1280) <- myreq_handler (cluster.c:654) <- vtask_entry (cluster.c:786)
FREED by T6: load_primary_config (config_repl.c:659, the 'free any prior decoded config before overwriting the pointer' step: free_ClusterConfig(myconf->cluster_config); free(myconf->cluster_config)) <- config_activate_committed (config_repl.c:360) <- handle_repl_config_push (config_repl.c:1280) <- myreq_handler <- vtask_entry
ALLOCATED by T5: calloc in decode_ClusterConfig_ptr (lib/controller.capnp.c:17074) <- load_cluster_config_from_file (config_repl.c:606) <- load_primary_config (config_repl.c:664) <- config_activate_committed <- handle_repl_config_push
This is a genuine, unguarded data race: load_primary_config's sequence is (a) if myconf->cluster_config is non-NULL, free it and NULL the pointer, then (b) decode a fresh ClusterConfig into myconf->cluster_config via load_cluster_config_from_file/decode_ClusterConfig_ptr. decode_ClusterConfig_ptr appears to publish the new struct pointer into *config (i.e. myconf->cluster_config) before it has finished populating nested fields (e.g. the Resource_list), since T5 is later observed still writing into the struct via decode_Resource_list AFTER T6 already saw a non-NULL myconf->cluster_config, freed it (T6's own step (a)), and proceeded to decode its own replacement. No mutex protects myconf->cluster_config across this read-free-decode sequence, so two overlapping invocations of handle_repl_config_push -> config_activate_committed -> load_primary_config for the same node race on the shared myconf->cluster_config pointer. This matches the class of concern already flagged (but not as a crash) in bug-976/bug-981 (handle_repl_config_push / config_activate_committed activation-ordering races) -- this is a NEW, more severe manifestation: an actual heap-corruption crash, not just an ordering/verification gap. Plausible trigger in this specific soak: heavy duplicate/late-joiner reconnect churn was independently observed on ctrl-2 (the primary) around the same window (bug-1474's WARN 'reusing guard-holding slot' fired twice, confirming the still-open, out-of-scope ha.c heartbeat-reconnect-sweep defect -- bug-1474's un-addressed 'fix angle (a)' -- was actively spawning duplicate/late-joiner standby connections during this round). If the primary sent the same config-push payload to ctrl-3 twice (once per duplicate connection), ctrl-3 could dispatch two concurrent handle_repl_config_push invocations on separate VTASK_LIVE_BLOCK workers, which is consistent with the observed T5/T6 race. This causal link (duplicate-connection churn -> duplicate config-push delivery -> concurrent load_primary_config race) is a plausible hypothesis from timeline correlation, not confirmed by direct evidence of two inbound config-push messages -- flagged as a hypothesis for whoever investigates, not a proven mechanism.

## Fix
FIXED (2026-07-28). Two-part fix in load_primary_config() (config_repl.c), independently reviewed and verified via a real pthread-based deterministic race test: (1) added myconf_t.lock (mylock_t, mirrors replicator_t.lock's idiom in repl.c) serializing the entire free-decode-publish sequence against any concurrent load_primary_config() call for the same myconf_t -- initialized in main.c before first use, finalized in myconf_fini(), and in the t43_attach_myconf/t43_free_myconf test fixture. (2) load_cluster_config_from_file() now decodes into a LOCAL temporary (cluster_config_t *tmp), never directly into the shared myconf->cluster_config field -- decode_ClusterConfig_ptr (lib/controller.capnp.c) calloc's and publishes its pointer via the out-parameter BEFORE decode_ClusterConfig populates nested fields (e.g. resources), so decoding into a local closes the early-publish exposure at its source; myconf->cluster_config is only swapped in after the new config is fully decoded and validated, still under myconf->lock. Part (2) is independently necessary because several other readers (cluster.c, queue.c, sched.c, worker.c, apiserver.c, ctrlstatus.c, reply.c) read c->myconf->cluster_config without ever taking myconf->lock, so the field itself must never be observably half-decoded. New regression test test_bug1476_concurrent_load_primary_config_no_uaf_or_double_free (test_config_repl.c) drives two REAL concurrent pthreads through load_primary_config() for the same myconf_t via a deterministic test-only hook (load_primary_config_race_hook, XCE_TESTING-only, NULL/no-op in production) that parks the first thread exactly at the retire-old-config step the live crash raced -- pre-fix this reliably reproduces a genuine ASan-catchable double-free from the same missing-lock root cause; post-fix myconf->lock keeps the second thread blocked for the entire duration, verified both by a captured never-raced-through flag and by the final published config being fully valid, never torn. Full suite: 1035 -> 1036 tests, 0 failures.

[UPDATE 2026-07-28, kiro-impl config-upgrade-snapshot resume] Prior fix landed with a comment block (config_repl.c:639-646) admitting it had been reverted to a RED-phase reproduction (no lock, decode-directly-into-shared-field) for test-construction purposes and NEVER restored to GREEN — the mylock_init/fini wiring (myconf.h, main.c, myconf.c) landed, but load_primary_config() itself still ran fully unguarded. Full suite run confirmed: test_bug1476_concurrent_load_primary_config_no_uaf_or_double_free FAILED ("thread B... Expected 0 Was 1"), i.e. B raced through while A was parked -- the lock was never acquired. Fixed for real: mylock_lock(&myconf->lock) now wraps the ENTIRE load_primary_config() body (acquired first, released at every return including success), and Cap-n-Proto decode now targets a local cluster_config_t *new_config first -- myconf->cluster_config is only freed+swapped after new_config is fully decoded and validated (reserved-name check, generation default), never decoded directly into the shared field. Verified 4/4 clean full-suite runs (1036 Tests 0 Failures 0 Ignored, ASAN_OPTIONS=detect_leaks=0) after the fix, including the specific race test. Committed as part of config-upgrade-snapshot task 8.6/8.9 unblock resume.

## Verification
_Not recorded (migrated from buglog.json)._

## References
- Related: bug-976, bug-981, bug-1474, bug-1475