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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: netdev@vger.kernel.org, Xiang Mei , Weiming Shi Subject: [PATCH net v2] vxlan: fix NULL dereference in vxlan_igmp_join() and vxlan_igmp_leave() Date: Mon, 23 Mar 2026 17:55:47 +0800 Message-ID: <20260323095544.3311285-4-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vxlan_sock_add() tolerates IPv6 socket creation failure with -EAFNOSUPPORT and brings the VXLAN device up with only an IPv4 socket, leaving vn6_sock as NULL. However, vxlan_igmp_join() and vxlan_igmp_leave() unconditionally dereference vn6_sock when handling multicast group operations for IPv6. When a VNI filter entry with an IPv6 multicast group is added via RTM_NEWTUNNEL on a collect-metadata VXLAN device where the IPv6 socket was not created, the NULL vn6_sock pointer is dereferenced, causing a kernel crash. This can be triggered by booting with ipv6.disable=1, creating a collect-metadata VXLAN device with vnifilter, and adding a VNI filter entry with an IPv6 multicast group. BUG: kernel NULL pointer dereference, address: 0000000000000010 Oops: Oops: 0000 [#1] SMP NOPTI RIP: 0010:vxlan_igmp_join (drivers/net/vxlan/vxlan_multicast.c:40) Call Trace: vxlan_vni_update_group (drivers/net/vxlan/vxlan_vnifilter.c:573) vxlan_vnifilter_process (drivers/net/vxlan/vxlan_vnifilter.c:976) rtnetlink_rcv_msg (net/core/rtnetlink.c:6986) netlink_rcv_skb (net/netlink/af_netlink.c:2550) rtnetlink_rcv (net/core/rtnetlink.c:7005) netlink_unicast (net/netlink/af_netlink.c:1344) netlink_sendmsg (net/netlink/af_netlink.c:1894) ____sys_sendmsg (net/socket.c:2592) ___sys_sendmsg (net/socket.c:2648) __sys_sendmsg (net/socket.c:2678) do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) Fix this by adding NULL checks for vn6_sock in both vxlan_igmp_join() and vxlan_igmp_leave() before dereferencing. Return 0 rather than an error code because all callers treat non-zero returns as fatal -- vxlan_vni_update_group() would abort a VNI add that already inserted into the hash table, and vxlan_multicast_join_vnigrp() would fail vxlan_open(). Since vxlan_sock_add() already accepts -EAFNOSUPPORT as a non-error condition, the multicast helpers should do the same by simply skipping the join/leave when the socket is absent. Fixes: f9c4bb0b245c ("vxlan: vni filtering support on collect metadata device") Reported-by: Xiang Mei Signed-off-by: Weiming Shi --- v2: - Drop unnecessary sock4 NULL checksjjj --- drivers/net/vxlan/vxlan_multicast.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/net/vxlan/vxlan_multicast.c b/drivers/net/vxlan/vxlan_multicast.c index a7f2d67dc61b8..a442c9e6d1a72 100644 --- a/drivers/net/vxlan/vxlan_multicast.c +++ b/drivers/net/vxlan/vxlan_multicast.c @@ -37,6 +37,8 @@ int vxlan_igmp_join(struct vxlan_dev *vxlan, union vxlan_addr *rip, } else { struct vxlan_sock *sock6 = rtnl_dereference(vxlan->vn6_sock); + if (!sock6) + return 0; sk = sock6->sock->sk; lock_sock(sk); ret = ipv6_stub->ipv6_sock_mc_join(sk, ifindex, @@ -71,6 +73,8 @@ int vxlan_igmp_leave(struct vxlan_dev *vxlan, union vxlan_addr *rip, } else { struct vxlan_sock *sock6 = rtnl_dereference(vxlan->vn6_sock); + if (!sock6) + return 0; sk = sock6->sock->sk; lock_sock(sk); ret = ipv6_stub->ipv6_sock_mc_drop(sk, ifindex, -- 2.43.0