From 46bf534cafc2b6a8fce1dd903cbe7672d3b2d7b0 Mon Sep 17 00:00:00 2001
From: Michael Tuexen <tuexen@FreeBSD.org>
Date: Mon, 15 Jan 2018 21:59:20 +0000
Subject: [PATCH] Don't provide a (meaningless) cmsg when proving a
 notification in a recvmsg() call.

MFC after:	1 week
---
 sys/netinet/sctputil.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/sys/netinet/sctputil.c b/sys/netinet/sctputil.c
index 5a004a14962..1ccd886c37c 100644
--- a/sys/netinet/sctputil.c
+++ b/sys/netinet/sctputil.c
@@ -47,7 +47,7 @@ __FBSDID("$FreeBSD$");
 #include <netinet/sctp_output.h>
 #include <netinet/sctp_uio.h>
 #include <netinet/sctp_timer.h>
-#include <netinet/sctp_indata.h>/* for sctp_deliver_data() */
+#include <netinet/sctp_indata.h>
 #include <netinet/sctp_auth.h>
 #include <netinet/sctp_asconf.h>
 #include <netinet/sctp_bsd_addr.h>
@@ -6094,7 +6094,7 @@ sctp_m_free(struct mbuf *m)
 	return (m_free(m));
 }
 
-void 
+void
 sctp_m_freem(struct mbuf *mb)
 {
 	while (mb != NULL)
@@ -6164,6 +6164,7 @@ sctp_soreceive(struct socket *so,
 	struct sockaddr *from;
 	struct sctp_extrcvinfo sinfo;
 	int filling_sinfo = 1;
+	int flags;
 	struct sctp_inpcb *inp;
 
 	inp = (struct sctp_inpcb *)so->so_pcb;
@@ -6191,15 +6192,24 @@ sctp_soreceive(struct socket *so,
 	if (filling_sinfo) {
 		memset(&sinfo, 0, sizeof(struct sctp_extrcvinfo));
 	}
-	error = sctp_sorecvmsg(so, uio, mp0, from, fromlen, flagsp,
+	if (flagsp != NULL) {
+		flags = *flagsp;
+	} else {
+		flags = 0;
+	}
+	error = sctp_sorecvmsg(so, uio, mp0, from, fromlen, &flags,
 	    (struct sctp_sndrcvinfo *)&sinfo, filling_sinfo);
+	if (flagsp != NULL) {
+		*flagsp = flags;
+	}
 	if (controlp != NULL) {
 		/* copy back the sinfo in a CMSG format */
-		if (filling_sinfo)
+		if (filling_sinfo && ((flags & MSG_NOTIFICATION) == 0)) {
 			*controlp = sctp_build_ctl_nchunk(inp,
 			    (struct sctp_sndrcvinfo *)&sinfo);
-		else
+		} else {
 			*controlp = NULL;
+		}
 	}
 	if (psa) {
 		/* copy back the address info */