26.7.6: unbound (and syslog-ng) segfault with signal 11 after upgrade (Hyper-V)

[Nex VII]

Hi,
after upgrading from 26.7.5 to 26.7.6 today, unbound keeps crashing with signal 11, roughly every 6-15 minutes, both at startup and at runtime.

Environment:
- OPNsense 26.7.6 (amd64), VM on Hyper-V
- unbound 1.26.1, unchanged since 18/09 and stable until today
- Unbound with DNSSEC, prefetch, serve-expired, aggressive NSEC, forwarding (DoT); DHCP lease registration off; DNSBL off

Observed (kernel log):
- unbound: 14x "exited on signal 11" since the upgrade, e.g. 19:29, 19:35, 19:41, 19:53, 19:59, 20:10, 20:18
- syslog-ng: 2x signal 11 right after boot
- python3.13: 2x signal 6 (abort)
- No "exited on signal" entries at all in the logs of the previous 4 weeks (since 10/09)
- Unbound logs nothing before dying: the last lines are normal resolution activity. A reboot doesn't help.

Since several unrelated binaries started segfaulting right after the update, this looks like a regression in base/libs rather than in unbound itself. Is anyone else seeing this on 26.7.6? I can enable kern.coredump and provide a backtrace if useful.

Thanks

[franco]

I have the feeling this is about https://github.com/opnsense/src/issues/297 which was supposed to be solved with 26.7.6, not cause more regressions on previously unaffected installs.

Can you try to confirm by downgrading the kernel?

# opnsense-update -zkr 26.7.4
(reboot)


Cheers,
Franco

[Nex VII]

Thanks Franco.

Host: Intel Xeon E-2236, Hyper-V Gen 2 VM with 4 vCPUs and 8 GB static RAM.

What I did:
- opnsense-revert -r 26.7.5 opnsense
- opnsense-update -bk -r 26.7.4
- reboot at 20:58

Current versions: core 26.7.5, base 26.7.4, kernel 26.7.4.

Result: since the reboot (about 1 hour so far) there have been no "exited on signal" entries at all. Before, on 26.7.6, unbound crashed repeatedly, the last time at 20:41.

I'll keep monitoring and will report back here if any crash happens again.

Cheers

[mnaim]

Same problem on Hyper-V.
Other physical machines are ok, no Unbound crashes.

[Monviech (Cedrik)]

I let AI run over this, take with a grain of salt (could, would...)

Two potential issues in sys/dev/hyperv/vmbus/hyperv_mmu.c:

* In hv_vm_tlb_flush(), (end == 0 || ...) > max_gvas compares a Boolean against max_gvas, making the condition always false and preventing full TLB flushes.
* In hv_flush_tlb_others_ex(), fill_gva_list() receives end, start instead of start, end, potentially invalidating the wrong page.

Both could leave stale TLB entries and explain the crashes.

[franco]

@Nex VII

Can you lock the kernel at 26.7.4 and update the rest back to 26.7.6? It would help narrowing this down before building a kernel that has the relevant commit reverted.


Thanks,
Franco

[franco]

@Monviech, yes both of these appear to be wrong...

https://github.com/opnsense/src/commit/412e76211e74ab

[Mabub]

Hi,

I'm seeing the same thing on Hyper-V, though less frequently than described here.

Environment:

OPNsense 26.7.6-amd64, FreeBSD 15.1-RELEASE-p4, OpenSSL 3.5.9
Virtualized on Hyper-V (host CPU: AMD EPYC 4584PX), VM with 8 GB RAM
Unbound 1.26.1 (since 18/09), Python module with dnsbl_module loaded
[Upgraded to 26.7.6 on: ...]

What I observe:

Today, 2026-10-09 04:15:53, kernel log:
pid 19272 (unbound), jid 0, uid 59: exited on signal 11 (no core dump - denied by kern.coredump)
The VM had rebooted at about 04:10 and Unbound started cleanly at 04:10:55. It crashed roughly 5 minutes later.
The resolver log shows nothing unusual before the crash. The last line is dnsbl_module: successfully opened pipe at 04:11:05, then silence until "Closing logger".
Earlier unclean death on 2026-10-04 at 03:01:31: the resolver log shows "Closing logger" without the usual "service stopped", and no restart afterwards. Unbound was apparently down until I rebooted on 2026-10-09 01:16, so about 5 days without DNS resolution from OPNsense. I can't confirm a signal 11 for that one, since my kernel log excerpt has no matching entry.
I restarted Unbound manually after noticing it was stopped on the dashboard.

I have not downgraded the kernel yet. Reverting to 26.7.5...

Thanks

[franco]

I've built a test kernel with the mentioned commit:

# opnsense-update -zkr 26.7.6-hyperv


Cheers,
Franco