Patch "ipv6: Fix SO_REUSEPORT UDP socket with implicit sk_ipv6only" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

ipv6: Fix SO_REUSEPORT UDP socket with implicit sk_ipv6only

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ipv6-fix-so_reuseport-udp-socket-with-implicit-sk_ipv6only.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Martin KaFai Lau <[email protected]>
Date: Wed, 24 Jan 2018 23:15:27 -0800
Subject: ipv6: Fix SO_REUSEPORT UDP socket with implicit sk_ipv6only

From: Martin KaFai Lau <[email protected]>

[ Upstream commit 7ece54a60ee2ba7a386308cae73c790bd580589c ]

If a sk_v6_rcv_saddr is !IPV6_ADDR_ANY and !IPV6_ADDR_MAPPED, it implicitly implies it is an ipv6only socket. However, in inet6_bind(), this addr_type checking and setting sk->sk_ipv6only to 1 are only done after sk->sk_prot->get_port(sk, snum) has been completed successfully.

This inconsistency between sk_v6_rcv_saddr and sk_ipv6only confuses the 'get_port()'.

In particular, when binding SO_REUSEPORT UDP sockets, udp_reuseport_add_sock(sk,...) is called. udp_reuseport_add_sock() checks "ipv6_only_sock(sk2) == ipv6_only_sock(sk)" before adding sk to sk2->sk_reuseport_cb. In this case, ipv6_only_sock(sk2) could be 1 while ipv6_only_sock(sk) is still 0 here. The end result is, reuseport_alloc(sk) is called instead of adding sk to the existing sk2->sk_reuseport_cb.

It can be reproduced by binding two SO_REUSEPORT UDP sockets on an IPv6 address (!ANY and !MAPPED). Only one of the socket will receive packet.

The fix is to set the implicit sk_ipv6only before calling get_port(). The original sk_ipv6only has to be saved such that it can be restored in case get_port() failed. The situation is similar to the inet_reset_saddr(sk) after get_port() has failed.

Thanks to Calvin Owens <[email protected]> who created an easy reproduction which leads to a fix.

---
 net/ipv6/af_inet6.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

@@ -284,6 +284,7 @@ int inet6_bind(struct socket *sock, stru
 	struct net *net = sock_net(sk);
 	__be32 v4addr = 0;
 	unsigned short snum;
+	bool saved_ipv6only;
 	int addr_type = 0;
 	int err = 0;
 

@@ -389,19 +390,21 @@ int inet6_bind(struct socket *sock, stru
 	if (!(addr_type & IPV6_ADDR_MULTICAST))
 		np->saddr = addr->sin6_addr;
 
+	saved_ipv6only = sk->sk_ipv6only;
+	if (addr_type != IPV6_ADDR_ANY && addr_type != IPV6_ADDR_MAPPED)
+		sk->sk_ipv6only = 1;
+
 	/* Make sure we are allowed to bind here. */
 	if ((snum || !inet->bind_address_no_port) &&
 	    sk->sk_prot->get_port(sk, snum)) {
+		sk->sk_ipv6only = saved_ipv6only;
 		inet_reset_saddr(sk);
 		err = -EADDRINUSE;
 		goto out;
 	}
 
-	if (addr_type != IPV6_ADDR_ANY) {
+	if (addr_type != IPV6_ADDR_ANY)
 		sk->sk_userlocks |= SOCK_BINDADDR_LOCK;
-		if (addr_type != IPV6_ADDR_MAPPED)
-			sk->sk_ipv6only = 1;
-	}
 	if (snum)
 		sk->sk_userlocks |= SOCK_BINDPORT_LOCK;
 	inet->inet_sport = htons(inet->inet_num);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/ipv6-fix-so_reuseport-udp-socket-with-implicit-sk_ipv6only.patch