[PATCH 5.10 051/491] net: vxlan: fix nd_tbl NULL dereference when IPv6 is disabled

Greg Kroah-Hartman
2026-04-13T16:44:49Z

From: Fernando Fernandez Mancera <fmancera@suse.de>

[ Upstream commit 168ff39e4758897d2eee4756977d036d52884c7e ]

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>
Link: https://patch.msgid.link/20260304120357.9778-2-fmancera@suse.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 7973d4070ee3b..c24535dc051c0 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2258,6 +2258,11 @@ 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);
--
2.51.0