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

On 3/5/26 12:39 PM, Ido Schimmel wrote:

On Wed, Mar 04, 2026 at 01:03:56PM +0100, Fernando Fernandez Mancera wrote:

quoted

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 <redacted>
Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=utE2H2VTX5nqfgs7LDxQ@mail.gmail.com/ (local)
Signed-off-by: Fernando Fernandez Mancera <redacted>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

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

Yes, a patch series dropping ipv6_stub is cooking.