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

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 <[email protected]>
> ---
> 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.