---
id: "bug-1746"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "controller"
severity: "crash"
timestamp: "2026-09-01T00:00:00Z"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 2
files: ["src/controller/persist.c"]
tags: ["worker-rejoin-resync", "task-2.2", "persist-c", "wal-job-dispatch", "bug-1678", "bug-1745", "null-pointer-deref", "asan", "record_job_reconcile_assign_fact"]
related: ["bug-1678", "bug-1745", "bug-1631"]
legacy: true
---

# bug-1746: worker-rejoin-resync task 2.2 implementation: persist_submit_job_dispatch_fact(p, jobid, state…

## Description
worker-rejoin-resync task 2.2 implementation: persist_submit_job_dispatch_fact(p, jobid, state, ts, alloc=NULL) crashes with a NULL-pointer SEGV instead of producing the "no allocation" WAL_JOB_DISPATCH payload design.md (Data Models / Out-of-Boundary section) and bug-1745's own design-review fix claimed was already "a tested NULL-alloc path" reusable verbatim. Confirmed via AddressSanitizer: SEGV on unknown address 0x0 in encode_JobAlloc (lib/controller.capnp.c:9805), called from capnp_encode_joballoc (controller/persist.c:235), called from persist_submit_job_dispatch_fact (controller/persist.c:7856), called from the new record_job_reconcile_assign_fact (controller/job.c) -- reproduced twice, deterministically, both via the full meson controller-test suite and via an isolated -t test_worker_resync run.

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

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

## Root cause
persist_submit_job_dispatch_fact() (persist.c:7844) unconditionally calls capnp_encode_joballoc(alloc, ...) regardless of whether alloc is NULL. capnp_encode_joballoc() (persist.c:225) calls encode_JobAlloc(cs, &cja, (xce_job_alloc_t*)a) directly -- NOT the NULL-safe encode_JobAlloc_ptr() wrapper that already exists in the same generated file (lib/controller.capnp.c:9388, used correctly by every OTHER encode call site) and already has an explicit NULL guard (if s==NULL, sets a capn_null pointer instead of encoding). encode_JobAlloc() itself (lib/controller.capnp.c:9322, generated capnp binding) has no NULL guard at all: its first statement dereferences its xce_job_alloc_t* parameter unconditionally (reads s->jobid). design.md (worker-rejoin-resync) and bug-1745's own design-validation fix pass both asserted this call is safe -- quoting design.md: bug-1678 already gave WAL_JOB_DISPATCH a persist_submit_job_dispatch_fact() primitive with both apply seams decoding an optional trailing JobAlloc, a NULL alloc being the documented, tested backward-compatible case -- but that claim conflates two different things: the DECODE/apply seams (apply_committed_entry, apply_wal_entry) genuinely ARE NULL-safe and tested for a payload with no trailing alloc bytes (test_wal_job_dispatch_fact.c constructs such payloads by hand, e.g. test_wjd_apply_committed_entry_transitions_pend_to_run) -- but NO existing test, and no existing production call site (dispatch_a_job_ is the only one, job.c:1731, and it always passes a freshly-calloc'd non-NULL j->job.allocs), ever calls persist_submit_job_dispatch_fact() itself with alloc=NULL. The function's own doc comment (persist.h, near line 1447) actually states the opposite precondition: alloc must be non-NULL, the real call site (dispatch_a_job_) always has one by construction. The ENCODE side was never made NULL-safe when bug-1678 fixed the DECODE side.

## Fix
FIXED (coordinator-authorized scope expansion of worker-rejoin-resync task 2.2 to include exactly this one function in persist.c, mirroring task 1.1's typemap.h/clusterconfig.h expansion precedent -- no schema or generated-code change). Added a NULL guard as the first statement of capnp_encode_joballoc() (persist.c:225): `if (a == NULL) { *out = NULL; *out_len = 0; return 0; }`. Produces a genuinely ZERO-LENGTH buffer for NULL input -- NOT a capnp-encoded null-pointer JobAlloc (what the existing encode_JobAlloc_ptr() wrapper's NULL branch would produce, which is non-zero bytes on the wire). This distinction is load-bearing: both apply seams (apply_committed_entry persist.c:4206-4227, apply_wal_entry persist.c:4759-4781) discriminate 'is there an allocation to decode' purely by `alloc_len > 0` on the trailing bytes after the {jobid,state[,start_time]} header -- a non-zero null-pointer-encoding byte count would have been misdecoded as a real (if empty/garbage) allocation to adopt, silently producing a non-NULL-but-garbage job.allocs on replay instead of the required NULL. Verified: (1) record_job_reconcile_assign_fact()'s 2 new tests (test_reconcile_assign_applies_running_no_allocs_and_notifies, test_reconcile_assign_survives_restart_replay -- the latter exercising a real disk WAL append + persist_recover() restart-replay round trip) now PASS cleanly, no SEGV. (2) record_job_reconcile_pending_fact()'s 3 existing task-2.1 tests still PASS unchanged. (3) dispatch_a_job_()'s existing non-NULL-alloc call site (job.c:1731, the only other caller) is completely unaffected -- its 5 dispatch-commit tests in test_dispatch_commit.c (test_dc_success_commits_alloc_state_and_resets_counter, test_dc_success_stamps_start_time_synchronously, test_dc_success_notifies_job_update_hook_exactly_once, test_dc_worker_not_found_leaves_job_pend_and_alloc_uncommitted, and critically test_dc_success_appends_wal_job_dispatch_durably -- a real disk WAL + persist_recover() round trip through the non-NULL-alloc path) all still PASS unchanged, confirming the new guard is a pure early-return for the NULL case with zero effect on the non-NULL path. (4) Full controller test suite (meson test -C src/xce.build 'controller test'): 6/6 OK, zero regressions anywhere. Also confirmed no secondary UBSan issue from the resulting `memcpy(dst, NULL, 0)` in persist_submit_job_dispatch_fact() when alloclen==0 (allocbuf stays NULL) -- this build runs under UBSAN_OPTIONS=halt_on_error=1 and the full suite passed clean, so glibc's memcpy tolerates a NULL/0 call here in practice.

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

## References
- Related: bug-1678, bug-1745, bug-1631