Subject: Re: [PATCH 1/2 net v3] net: bridge: fix nd_tbl NULL dereference when IPv6 is disabled

From: Ido Schimmel <[email-masked]>
Date: Thu, 5 Mar 2026 13:39:40 +0200

On Wed, Mar 04, 2026 at 01:03:56PM +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. Then, if neigh_suppress is enabled and an ICMPv6
> Neighbor Discovery packet reaches the bridge, br_do_suppress_nd() will
> dereference ipv6_stub->nd_tbl which is NULL, passing it to
> neigh_lookup(). This causes a kernel NULL pointer dereference.
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000268
>  Oops: 0000 [#1] PREEMPT SMP NOPTI
>  [...]
>  RIP: 0010:neigh_lookup+0x16/0xe0
>  [...]
>  Call Trace:
>   <IRQ>
>   ? neigh_lookup+0x16/0xe0
>   br_do_suppress_nd+0x160/0x290 [bridge]
>   br_handle_frame_finish+0x500/0x620 [bridge]
>   br_handle_frame+0x353/0x440 [bridge]
>   __netif_receive_skb_core.constprop.0+0x298/0x1110
>   __netif_receive_skb_one_core+0x3d/0xa0
>   process_backlog+0xa0/0x140
>   __napi_poll+0x2c/0x170
>   net_rx_action+0x2c4/0x3a0
>   handle_softirqs+0xd0/0x270
>   do_softirq+0x3f/0x60
> 
> Fix this by replacing IS_ENABLED(IPV6) call with ipv6_mod_enabled() in
> the callers. This is in essence disabling NS/NA suppression when IPv6 is
> disabled.
> 
> Fixes: ed842faeb2bd ("bridge: suppress nd pkts on BR_NEIGH_SUPPRESS ports")
> Reported-by: Guruprasad C P <[email-masked]>
> Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=[email-masked]/
> Signed-off-by: Fernando Fernandez Mancera <[email-masked]>

Reviewed-by: Ido Schimmel <[email-masked]>

I assume you will remove ipv6_stub from the bridge in net-next