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

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

[Fernando Fernandez Mancera]

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 <gurucp2005@gmail.com>
Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=utE2H2VTX5nqfgs7LDxQ@mail.gmail.com/
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
v2: use ipv6_mod_enabled() instead of a null check and replace the check
on the caller
v3: no changes
---
 net/bridge/br_device.c | 2 +-
 net/bridge/br_input.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index ee01122f466f..f7502e62dd35 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -74,7 +74,7 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 	     eth_hdr(skb)->h_proto == htons(ETH_P_RARP)) &&
 	    br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED)) {
 		br_do_proxy_suppress_arp(skb, br, vid, NULL);
-	} else if (IS_ENABLED(CONFIG_IPV6) &&
+	} else if (ipv6_mod_enabled() &&
 		   skb->protocol == htons(ETH_P_IPV6) &&
 		   br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED) &&
 		   pskb_may_pull(skb, sizeof(struct ipv6hdr) +
diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index 1405f1061a54..2cbae0f9ae1f 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -170,7 +170,7 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
 	    (skb->protocol == htons(ETH_P_ARP) ||
 	     skb->protocol == htons(ETH_P_RARP))) {
 		br_do_proxy_suppress_arp(skb, br, vid, p);
-	} else if (IS_ENABLED(CONFIG_IPV6) &&
+	} else if (ipv6_mod_enabled() &&
 		   skb->protocol == htons(ETH_P_IPV6) &&
 		   br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED) &&
 		   pskb_may_pull(skb, sizeof(struct ipv6hdr) +
-- 
2.53.0

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

[Fernando Fernandez Mancera]

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. If an IPv6 packet is injected into the interface,
route_shortcircuit() is called and a NULL pointer dereference happens on
neigh_lookup().

 BUG: kernel NULL pointer dereference, address: 0000000000000380
 Oops: Oops: 0000 [#1] SMP NOPTI
 [...]
 RIP: 0010:neigh_lookup+0x20/0x270
 [...]
 Call Trace:
  <TASK>
  vxlan_xmit+0x638/0x1ef0 [vxlan]
  dev_hard_start_xmit+0x9e/0x2e0
  __dev_queue_xmit+0xbee/0x14e0
  packet_sendmsg+0x116f/0x1930
  __sys_sendto+0x1f5/0x200
  __x64_sys_sendto+0x24/0x30
  do_syscall_64+0x12f/0x1590
  entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fix this by adding an early check on route_shortcircuit() when protocol
is ETH_P_IPV6. Note that ipv6_mod_enabled() cannot be used here because
VXLAN can be built-in even when IPv6 is built as a module.

Fixes: e15a00aafa4b ("vxlan: add ipv6 route short circuit support")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
v2: use ipv6_mod_enabled() instead of a NULL check
v3: go back to nd_tbl NULL check as ipv6_mod_enabled() might not be
available. Added a comment so it doesn't seem random.
---
 drivers/net/vxlan/vxlan_core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 05558b6afecd..17c941aac32d 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2130,6 +2130,11 @@ static bool route_shortcircuit(struct net_device *dev, struct sk_buff *skb)
 	{
 		struct ipv6hdr *pip6;
 
+		/* check if nd_tbl is not initiliazed due to
+		 * ipv6.disable=1 set during boot
+		 */
+		if (!ipv6_stub->nd_tbl)
+			return false;
 		if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 			return false;
 		pip6 = ipv6_hdr(skb);
-- 
2.53.0

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

[Ido Schimmel]

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 <gurucp2005@gmail.com>
> Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=utE2H2VTX5nqfgs7LDxQ@mail.gmail.com/
> Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>

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

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

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

[Fernando Fernandez Mancera]

On 3/5/26 12:39 PM, Ido Schimmel wrote:
> 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 <gurucp2005@gmail.com>
>> Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=utE2H2VTX5nqfgs7LDxQ@mail.gmail.com/
>> Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
> 
> 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.

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

[Nikolay Aleksandrov]

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 <gurucp2005@gmail.com>
> Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=utE2H2VTX5nqfgs7LDxQ@mail.gmail.com/
> Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
> ---
> v2: use ipv6_mod_enabled() instead of a null check and replace the check
> on the caller
> v3: no changes
> ---

Acked-by: Nikolay Aleksandrov <razor@blackwall.org>

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

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed,  4 Mar 2026 13:03:56 +0100 you 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.
> 
> [...]

Here is the summary with links:
  - [1/2,net,v3] net: bridge: fix nd_tbl NULL dereference when IPv6 is disabled
    https://git.kernel.org/netdev/net/c/e5e890630533
  - [2/2,net,v3] net: vxlan: fix nd_tbl NULL dereference when IPv6 is disabled
    https://git.kernel.org/netdev/net/c/168ff39e4758

You are awesome, thank you!
-- 
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