Re: [PATCH net] net: bridge: fix nd_tbl NULL dereference when IPv6 is disabled

Fernando Fernandez Mancera
2026-02-27T00:09:57Z

On 2/27/26 12:40 AM, 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 adding a check before br_is_local_ip6() or neigh_lookup()
> call. If ipv6_stub->nd_tbl is NULL, return immediately.
>
> Fixes: ed842faeb2bd ("bridge: suppress nd pkts on BR_NEIGH_SUPPRESS ports")
> Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=utE2H2VTX5nqfgs7LDxQ@mail.gmail.com/
> Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
> ---
> Note: I am investigating more places where this might be happening too.
> ---

I can confirm that there is at least one more instance of this problem.
Although it is not on bridge driver. I will send a patch ASAP.

Thanks,
Fernando.