ipv6: Fix handling of LLA with VRF and sockets bound to VRF

mainline inclusion
from mainline-v5.0-rc1
commit c2027d1e17582903e368abf5d4838b22a98f2b7b
category: bugfix
bugzilla: 9289
CVE: NA

-------------------------------------------------

A recent commit allows sockets bound to a VRF to receive ipv6 link local
packets. However, it only works for UDP and worse TCP connection attempts
to the LLA with the only listener bound to the VRF just hang where as
before the client gets a reset and connection refused. Fix by adjusting
ir_iif for LL addresses and packets received through a device enslaved
to a VRF.

Fixes: 6f12fa775530 ("vrf: mark skb for multicast or link-local as enslaved to VRF")
Reported-by: NDonald Sharp <sharpd@cumulusnetworks.com>
Cc: Mike Manning <mmanning@vyatta.att-mail.com>
Signed-off-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NKeefe LIU <liuqifa@huawei.com>
Reviewed-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/ipv6/tcp_ipv6.c

@@ -734,6 +734,7 @@ static void tcp_v6_init_req(struct request_sock *req,
 			    const struct sock *sk_listener,
 			    struct sk_buff *skb)
 {
+	bool l3_slave = ipv6_l3mdev_skb(TCP_SKB_CB(skb)->header.h6.flags);
 	struct inet_request_sock *ireq = inet_rsk(req);
 	const struct ipv6_pinfo *np = inet6_sk(sk_listener);
 
@@ -741,7 +742,7 @@ static void tcp_v6_init_req(struct request_sock *req,
 	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
 
 	/* So that link locals have meaning */
-	if (!sk_listener->sk_bound_dev_if &&
+	if ((!sk_listener->sk_bound_dev_if || l3_slave) &&
 	    ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
 		ireq->ir_iif = tcp_v6_iif(skb);