BIRD 3.1.5 crash: Assertion failure in do_lock / if_find_by_index

[Moraxyc]

Hi David,

Thanks for the confirmation and explanation.

I will upgrade to v3.2 as suggested. Thanks for your work!

Best regards,
Moraxyc

On Mon, Jan 05, 2026 at 11:00:21PM +0100, David Petera via Bird-users wrote:
> Hi,
>
> we looked into it and it really is a regression bug in the v3.1.5 connected
> to locking domains in BGP.
>
> The newly released v3.2 should not have this issue so I recommend using that
> version.
> Though v3.1.6 with the fix will be released also.
>
> Thanks a lot for reporting this bug to us!
> David
>
> David Petera (he/him) | BIRD Tech Support | CZ.NIC, z.s.p.o.
>
> On 12/11/25 18:50, Moraxyc via Bird-users wrote:
> > Hi BIRD Team,
> >
> > I wanna report a crash with BIRD 3.1.5 running on NixOS.
> >
> > The crash triggers a `bug()` assertion failure related to locking
> > mechanisms during interface lookup (`if_find_by_index`).
> >
> > I have successfully reproduced this issue locally with a minimal
> > configuration.
> >
> > Environment:
> > - BIRD Version: 3.1.5
> > - OS: NixOS unstable (glibc 2.40)
> > - Kernel: Linux 6.17.9 #1-NixOS SMP PREEMPT_DYNAMIC x86_64 GNU/Linux
> >
> > Reproduction Steps:
> > 1. Configure a BGP protocol using an IPv6 Link-Local neighbor on a
> > physical interface.
> > 2. Start BIRD. Wait for the protocol to enter 'Active' or 'Connect'
> > state so the port is listening.
> > 3. Initiate a TCP connection to the BGP port:
> >    $ nc -6 -v <Link-Local-IP>%<interface> <port>
> > 4. BIRD crashes immediately upon receiving the connection.
> >
> > Crash Summary (from GDB):
> > The main thread (Thread 1) hits a bug() assertion:
> > #3  0x000056536f6ef97a in bug (msg=<optimized out>) at
> > sysdep/unix/log.c:412
> > #4  0x000056536f6fa9a1 in do_lock (dg=0x5653774ace60,
> > lsp=0x7fba0208a2a8) at sysdep/unix/domain.c:116
> > #5  0x000056536f64c8ac in if_find_by_index (idx=23) at nest/iface.c:721
> > #6  0x000056536f6e4ac8 in sockaddr_read6 ... at sysdep/unix/io.c:583
> > #8  0x000056536f6ecfd7 in sk_passive_connected ... at
> > sysdep/unix/io.c:1451
> >
> > Attachments:
> > 1. backtrace.txt: Full GDB backtrace.
> > 2. config_snippet.txt: The minimal config used to reproduce the crash.
> >
> > Best regards,
> > Moraxyc