From: Eric Dumazet <edumazet@google.com>
Date: Tue, 1 Oct 2019 10:49:06 -0700
Subject: tcp: add ipv6_addr_v4mapped_loopback() helper
Patch-mainline: v5.5-rc1
Git-commit: be2644aac3e1db02d09f45d56206bbdafca582a2
References: bsc#1154353

tcp_twsk_unique() has a hard coded assumption about ipv4 loopback
being 127/8

Lets instead use the standard ipv4_is_loopback() method,
in a new ipv6_addr_v4mapped_loopback() helper.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/net/ipv6.h  |    5 +++++
 net/ipv4/tcp_ipv4.c |    6 ++----
 2 files changed, 7 insertions(+), 4 deletions(-)

--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -696,6 +696,11 @@ static inline bool ipv6_addr_v4mapped(co
 					cpu_to_be32(0x0000ffff))) == 0UL;
 }
 
+static inline bool ipv6_addr_v4mapped_loopback(const struct in6_addr *a)
+{
+	return ipv6_addr_v4mapped(a) && ipv4_is_loopback(a->s6_addr32[3]);
+}
+
 static inline u32 ipv6_portaddr_hash(const struct net *net,
 				     const struct in6_addr *addr6,
 				     unsigned int port)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -121,11 +121,9 @@ int tcp_twsk_unique(struct sock *sk, str
 #if IS_ENABLED(CONFIG_IPV6)
 		if (tw->tw_family == AF_INET6) {
 			if (ipv6_addr_loopback(&tw->tw_v6_daddr) ||
-			    (ipv6_addr_v4mapped(&tw->tw_v6_daddr) &&
-			     (tw->tw_v6_daddr.s6_addr[12] == 127)) ||
+			    ipv6_addr_v4mapped_loopback(&tw->tw_v6_daddr) ||
 			    ipv6_addr_loopback(&tw->tw_v6_rcv_saddr) ||
-			    (ipv6_addr_v4mapped(&tw->tw_v6_rcv_saddr) &&
-			     (tw->tw_v6_rcv_saddr.s6_addr[12] == 127)))
+			    ipv6_addr_v4mapped_loopback(&tw->tw_v6_rcv_saddr))
 				loopback = true;
 		} else
 #endif