sctp: add support for setting flowlabel when adding a transport

Struct sockaddr_in6 has the member sin6_flowinfo that includes the
ipv6 flowlabel, it should also support for setting flowlabel when
adding a transport whose ipaddr is from userspace.

Note that addrinfo in sctp_sendmsg is using struct in6_addr for
the secondary addrs, which doesn't contain sin6_flowinfo, and
it needs to copy sin6_flowinfo from the primary addr.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/associola.c

@@ -650,8 +650,16 @@ struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
 	peer->sackdelay = asoc->sackdelay;
 	peer->sackfreq = asoc->sackfreq;
 
-	if (addr->sa.sa_family == AF_INET6)
+	if (addr->sa.sa_family == AF_INET6) {
+		__be32 info = addr->v6.sin6_flowinfo;
+
+		if (info) {
+			peer->flowlabel = ntohl(info & IPV6_FLOWLABEL_MASK);
+			peer->flowlabel |= SCTP_FLOWLABEL_SET_MASK;
+		} else {
 			peer->flowlabel = asoc->flowlabel;
+		}
+	}
 	peer->dscp = asoc->dscp;
 
 	/* Enable/disable heartbeat, SACK delay, and path MTU discovery

net/sctp/socket.c

@@ -1697,6 +1697,7 @@ static int sctp_sendmsg_new_asoc(struct sock *sk, __u16 sflags,
 	struct sctp_association *asoc;
 	enum sctp_scope scope;
 	struct cmsghdr *cmsg;
+	__be32 flowinfo = 0;
 	struct sctp_af *af;
 	int err;
 
@@ -1781,6 +1782,9 @@ static int sctp_sendmsg_new_asoc(struct sock *sk, __u16 sflags,
 	if (!cmsgs->addrs_msg)
 		return 0;
 
+	if (daddr->sa.sa_family == AF_INET6)
+		flowinfo = daddr->v6.sin6_flowinfo;
+
 	/* sendv addr list parse */
 	for_each_cmsghdr(cmsg, cmsgs->addrs_msg) {
 		struct sctp_transport *transport;
@@ -1813,6 +1817,7 @@ static int sctp_sendmsg_new_asoc(struct sock *sk, __u16 sflags,
 			}
 
 			dlen = sizeof(struct in6_addr);
+			daddr->v6.sin6_flowinfo = flowinfo;
 			daddr->v6.sin6_family = AF_INET6;
 			daddr->v6.sin6_port = htons(asoc->peer.port);
 			memcpy(&daddr->v6.sin6_addr, CMSG_DATA(cmsg), dlen);