sctp: check for ipv6_pinfo legal sndflow with flowlabel in sctp_v6_get_dst

The transport with illegal flowlabel should not be allowed to send
packets. Other transport protocols already denies this.
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/ipv6.c

@@ -262,6 +262,15 @@ static void sctp_v6_get_dst(struct sctp_transport *t, union sctp_addr *saddr,
 	if (t->flowlabel & SCTP_FLOWLABEL_SET_MASK)
 		fl6->flowlabel = htonl(t->flowlabel & SCTP_FLOWLABEL_VAL_MASK);
 
+	if (np->sndflow && (fl6->flowlabel & IPV6_FLOWLABEL_MASK)) {
+		struct ip6_flowlabel *flowlabel;
+
+		flowlabel = fl6_sock_lookup(sk, fl6->flowlabel);
+		if (!flowlabel)
+			goto out;
+		fl6_sock_release(flowlabel);
+	}
+
 	pr_debug("%s: dst=%pI6 ", __func__, &fl6->daddr);
 
 	if (asoc)