On 3/3/26 12:02 AM, Sabrina Dubroca wrote:
2026-03-02, 19:04:14 +0100, Fernando Fernandez Mancera wrote:
On 3/2/26 6:44 PM, Fernando Fernandez Mancera wrote:
On 3/2/26 5:36 PM, Ido Schimmel wrote:
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?
Yes, after Sabrina mentioned it that was what I planned to do. But on
VXLAN I want to avoid such patch for net tree as a fix. Instead I
propose to use the __in6_dev_get() check as neigh_reduce() does.
I'm not convinced __in6_dev_get() makes more sense. It's also pretty
much a random NULL check to me, and at least with checking nd_tbl
directly it's clearly related to the code that follows.
In neigh_reduce(), __in6_dev_get() seems to have been present from the
start, and back then in6_dev was used in the function. Now, it might
easily be removed by a clean-up patch that doesn't notice it's useful.
Fair enough, let's just stick to the nd_tbl NULL check for now on VXLAN.
I will send a patch on net-next tree once this is merged to enforce
"depends on IPV6 || IPV6=n" and remove ipv6_stub from there.
I hope that sounds good to you all.
Should there be a helper ipv6_mod_available() (or a better name) in
net/ipv6/addrconf_core.c (so always available) to wrap those checks in
a way that doesn't rely on Kconfig magic nor non-obvious NULL checks?
(maybe even replacing ipv6_mod_enabled()?)
Maybe yes, but not sure if it is worth it. As discussed here [1]
dropping IPv6 as a module seems like a good idea. Anyway, let's discuss
that topic there!
[1] https://lore.kernel.org/netdev/[email protected]/
Thanks,
Fernando.
Later,
do a follow-up patch on net-next tree removing ipv6_stub and enforcing
"depends on IPV6 || IPV6=n".
FWIW; removing the ipv6_stub won't keep us from checking ipv6_mod_enabled()
as ipv6.disable=1 can still be set at booting time and therefore nd_tbl will
still be non-initialized because ndisc_init() and neigh_table_init() are
never called.
Ok.
