[PATCH 2/2 net v2] net: vxlan: fix nd_tbl NULL dereference when IPv6 is disabled

Fernando Fernandez Mancera
2026-03-02T14:09:02Z

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.

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
---
drivers/net/vxlan/vxlan_core.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 05558b6afecd..5fee680e4a8b 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2130,6 +2130,8 @@ static bool route_shortcircuit(struct net_device *dev, struct sk_buff *skb)
{
struct ipv6hdr *pip6;

+ if (!ipv6_mod_enabled())
+ return false;
if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
return false;
pip6 = ipv6_hdr(skb);
--
2.53.0