---
id: "bug-1077"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "lib"
severity: "crash"
timestamp: "2026-06-24T17:30:00.000Z"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 1
files: ["src/lib/xcectx.c"]
tags: ["asan", "use-after-return", "union-type-confusion", "ha", "failover", "ctrlstatus", "libxce", "memory-safety", "regression-61e1391", "VERIFIED"]
related: ["bug-646", "bug-1060", "bug-1067"]
legacy: true
---

# bug-1077: AddressSanitizer: SEGV / stack-use-after-return in free_CtrlStatus (lib/controller.capnp.c:11638)…

## Description
AddressSanitizer: SEGV / stack-use-after-return in free_CtrlStatus (lib/controller.capnp.c:11638) via handle_reply -> free_CtrlStatus_ptr (lib/xcectx.c:91) on `ctrlstatus` after failover; READ derefs the dead-stack `getreply` of xce_get_with_condition (xceapi.c)

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

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

## Root cause
ctx->reply.u is an UNTAGGED union shared across opcodes (debugmsg/get/jobid/clusterconf/ctrlstatus alias the same 8 bytes). Commit 61e1391 ('fix bug-1060 bug-1067', unrelated Raft work) added speculative free-guards `if (ctx->reply.u.ctrlstatus) free_CtrlStatus_ptr(&ctx->reply.u.ctrlstatus)` (and the clusterconf twin). A non-NULL slot does NOT imply a CtrlStatus*: a failover-aborted reslist/joblist leaves ctx->reply.u.get == &getreply (a dead STACK pointer) because xce_get_with_condition/xce_resval only NULL the slot on the success path, not the xce_get_req<0 / cbuf_get<0 early-returns. The next ctrlstatus reply (worker thread) sees the foreign non-NULL slot and free_CtrlStatus walks it -> stack-use-after-return SEGV.

## Fix
1) Revert the two unsafe free-guards in handle_reply (untagged union slot can never be safely freed by type) — restores prior MOVE_PTR-overwrite behavior. 2) Clear ctx->reply.u.get = NULL on ALL early-return paths of xce_get_with_condition and xce_resval (kill the dangling-stack-pointer leak at its source; also prevents a late OPCode_get reply writing through the dead stack via handle_get_reply). 3) Defense-in-depth: handle_get_reply drops a reply when ctx->reply.u.get is NULL. Regression test: test_handle_reply_ctrlstatus_does_not_free_foreign_slot (exposes xce_handle_reply, proves a foreign heap value in the shared union is not freed). VERIFIED 2026-06-24 (Opus): re-confirmed 3-layer fix present in working tree; RED proven by re-injecting the ctrlstatus free-guard -> ASan double-free at test_ctrlstatus.c:384 (free_CtrlStatus_ptr at controller.capnp.c:11892), then restored -> GREEN. Full libxce suite 291 Tests / 0 Failures / 0 ASan errors under ASAN_OPTIONS=detect_leaks=0.

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

## References
- Related: bug-646, bug-1060, bug-1067