Fix use-after-free in sk_repl_idle()'s idle-tick VM resolution (FABRIC-3.md §XIII)

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Root-caused a heap-corruption bug that reliably failed WIREBIND identity
attach on the third attach/detach cycle in one boot. sk_console_readline()
and sk_console_getkey() captured `active_vm` once from their caller and
kept passing that same (possibly long-stale) pointer to sk_repl_idle() on
every idle tick serviced while blocked waiting for input. If the VM it
pointed at was killed (WIREBIND detach) mid-block, the existing bailout
only checked a generic "is anyone attached" boolean -- masked as soon as a
different identity attached next -- so blk_vm_flush_all() kept writing
into a freed VM struct sitting on kmalloc's own free list, corrupting the
free list's linked-list metadata itself.

Both idle branches now re-resolve the live active VM fresh from
g_repl_active_vm on every tick, matching the dispatch-side fix already
made for the sibling bug in §XII.3.

Verified: rebuilt amd64, reran the exact three-cycle repro that reliably
corrupted the heap before the fix -- free-list census stayed stable
through the same idle window that previously collapsed to zero. All three
architectures (amd64/aarch64/riscv64) boot clean to the zuse)ok> prompt.

kmalloc_debug_census()/kmalloc_debug_census_bytes() kept as permanent
diagnostic infrastructure; every other temporary probe added during the
investigation was reverted.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EXieurDfDSsDFdnSyusuWo

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This commit is contained in:

Robert Allan James

2026-09-10 20:30:41 -04:00

co-authored by Claude Sonnet 5

parent 70421bdd43

commit 9142dda2d6

38 changed files with 236983 additions and 3 deletions

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