Re: [PATCH 2/2 net v2] net: vxlan: fix nd_tbl NULL dereference when IPv6 is disabled

Ido Schimmel
2026-03-02T16:36:59Z

On Mon, Mar 02, 2026 at 04:13:14PM +0100, Fernando Fernandez Mancera wrote:
> On 3/2/26 3:43 PM, Sabrina Dubroca wrote:
> > 2026-03-02, 15:08:47 +0100, Fernando Fernandez Mancera wrote:
> > > When booting with the 'ipv6.disable=1' parameter, the nd_tbl is never
> > > initialized because inet6_init() exits before ndisc_init() is called
> > > which initializes it. If an IPv6 packet is injected into the interface,
> > > route_shortcircuit() is called and a NULL pointer dereference happens on
> > > neigh_lookup().
> >
> > VXLAN can be built-in even when IPv6 is built as a module, and then
> > ipv6_mod_enabled can't be used in VXLAN:
> >
> > ld: drivers/net/vxlan/vxlan_core.o: in function `route_shortcircuit':
> > drivers/net/vxlan/vxlan_core.c:2133:(.text+0x116e0): undefined reference to `ipv6_mod_enabled'
> >
> >
> > GENEVE has a Kconfig tweak to prevent this since 094be0927ff3
> > ("geneve: fix build with modular IPV6"):
> >
> > depends on IPV6 || !IPV6
> >
> > but VXLAN doesn't.
> >
>
> Ugh, good catch. Thanks Sabrina.
>
> > But then I think we don't need to use ipv6_stub at all.
>
> If we enforce "depends on IPV6 || IPV6=n" on VXLAN we could get rid of
> ipv6_stub completely and use direct calls instead.

I just noticed that this is already enforced for the bridge, so maybe
you can just remove ipv6_stub in patch #1?