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

Fernando Fernandez Mancera
2026-02-26T23:41:23Z

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.
---
net/bridge/br_arp_nd_proxy.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/net/bridge/br_arp_nd_proxy.c b/net/bridge/br_arp_nd_proxy.c
index 1e2b51769eec..ed756518cee0 100644
--- a/net/bridge/br_arp_nd_proxy.c
+++ b/net/bridge/br_arp_nd_proxy.c
@@ -437,6 +437,12 @@ void br_do_suppress_nd(struct sk_buff *skb, struct net_bridge *br,
return;
}

+ /* IPv6 disabled at boot, return before calling into br_is_local_ip6()
+ * or neigh_lookup()
+ */
+ if (!ipv6_stub->nd_tbl)
+ return;
+
if (vid != 0) {
/* build neigh table lookup on the vlan device */
vlandev = __vlan_find_dev_deep_rcu(br->dev, skb->vlan_proto,
--
2.53.0