[gburd]

libumem 4.3.2 fixes the bug behind F1-002 and F1-003, which we reported on 2026-11-04.

The bug. Under LD_PRELOAD, UMEM_DEBUG=audit, and default, which includes it, re-entered the allocator. The first stack walk on each thread called pthread_getattr_np() while vmem locks were held, and that call mallocs. The result was the VMC_POPULATOR abort on the dev box, or a hang on the Ubuntu 26.04 runner.

The fix. 4.3.2 reads the stack bounds from /proc/self/maps with plain open/read, so nothing on that path allocates. Commits: fix 490c943, regression test 4abe0f6, release 60a6452. The ABI is unchanged.

Measured on the dev box (Debian 12, x86_64), 25 runs per cell. Each library was first shown to be live by catching a planted overflow. The programs are the one-malloc reproducer and a first-malloc-on-a-new-thread variant.

UMEM_DEBUG	fe9ff96 (old pin)	60a6452 (v4.3.2)
audit	25/25 abort	25/25 exit 0
audit + norseq	25/25 hang	25/25 exit 0
default	25/25 abort	25/25 exit 0
default + norseq	25/25 hang	25/25 exit 0

s3 against master with 4.3.2. s3-umem is clean and s3-umem-sabotage catches the planted overflow on seeds 1–5, under both default and guards,contents. The edited script, run without S3_UMEM_MODE, picks default and passes both arms.

Changes:

• install.sh: LIBUMEM_PIN → 60a6452. This also changes the CI tools cache key, so CI rebuilds libumem.
• s3_alloc_failure.sh: UMEM_DEBUG=default again, so the audit allocation and free stacks are back in its reports. S3_UMEM_MODE=guards,contents still selects the old mode.
• FINDINGS.md: F1-002 and F1-003 are marked fixed upstream, with the measurements.
• README.md: the tool note now says 4.3.2 or later is required.

Every libumem run stays under timeout -k, as libumem's maintainers recommended: on one of their hosts a hung LD_PRELOAD process outlived a plain timeout.

Test-only. No engine change, so no LTS backport.

[github-actions]

Coccinelle convention checks

No new violations. ✅

Resolved since baseline (3) -- update dist/cocci/baseline.txt to lock these in.

rule_mutex_unbalanced|MUTEX_UNBALANCED|src/btree/bt_curadj.c|return (ret);
rule_mutex_unbalanced|MUTEX_UNBALANCED|src/crypto/mersenne/mt19937db.c|return (ret);
rule_mutex_unbalanced|MUTEX_UNBALANCED|src/mp/mp_register.c|return (ret);

[github-actions]

ABI diff vs v2026.10.8 (libabigail — authoritative)

abidiff exit bitmask: 0

Removed exported symbols (nm -D, _NNNN version suffix normalized)

None.

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Advisory: libabigail/nm is the authoritative binary-ABI check; Coccinelle is complementary source-level early warning. See dist/cocci/README.md.