net: sctp: implement rfc6458, 5.3.6. SCTP_NXTINFO cmsg support

This patch implements section 5.3.6. of RFC6458, that is, support
for 'SCTP Next Receive Information Structure' (SCTP_NXTINFO) which
is placed into ancillary data cmsghdr structure for each recvmsg()
call, if this information is already available when delivering the
current message.

This option can be enabled/disabled via setsockopt(2) on SOL_SCTP
level by setting an int value with 1/0 for SCTP_RECVNXTINFO in
user space applications as per RFC6458, section 8.1.30.

The sctp_nxtinfo structure is defined as per RFC as below ...

  struct sctp_nxtinfo {
    uint16_t nxt_sid;
    uint16_t nxt_flags;
    uint32_t nxt_ppid;
    uint32_t nxt_length;
    sctp_assoc_t nxt_assoc_id;
  };

... and provided under cmsg_level IPPROTO_SCTP, cmsg_type
SCTP_NXTINFO, while cmsg_data[] contains struct sctp_nxtinfo.

Joint work with Daniel Borkmann.

Signed-off-by: Geir Ola Vaagland <geirola@gmail.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 38 insertions, 0 deletions

diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
index b31f365f18ab..e049298ecfa0 100644
--- a/net/sctp/ulpevent.c
+++ b/net/sctp/ulpevent.c
@@ -911,6 +911,44 @@ void sctp_ulpevent_read_rcvinfo(const struct sctp_ulpevent *event,
 		 sizeof(rinfo), &rinfo);
 }
 
+/* RFC6458, Section 5.3.6. SCTP Next Receive Information Structure
+ * (SCTP_NXTINFO)
+ */
+static void __sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
+					 struct msghdr *msghdr,
+					 const struct sk_buff *skb)
+{
+	struct sctp_nxtinfo nxtinfo;
+
+	memset(&nxtinfo, 0, sizeof(nxtinfo));
+	nxtinfo.nxt_sid = event->stream;
+	nxtinfo.nxt_ppid = event->ppid;
+	nxtinfo.nxt_flags = event->flags;
+	if (sctp_ulpevent_is_notification(event))
+		nxtinfo.nxt_flags |= SCTP_NOTIFICATION;
+	nxtinfo.nxt_length = skb->len;
+	nxtinfo.nxt_assoc_id = sctp_assoc2id(event->asoc);
+
+	put_cmsg(msghdr, IPPROTO_SCTP, SCTP_NXTINFO,
+		 sizeof(nxtinfo), &nxtinfo);
+}
+
+void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
+				struct msghdr *msghdr,
+				struct sock *sk)
+{
+	struct sk_buff *skb;
+	int err;
+
+	skb = sctp_skb_recv_datagram(sk, MSG_PEEK, 1, &err);
+	if (skb != NULL) {
+		__sctp_ulpevent_read_nxtinfo(sctp_skb2event(skb),
+					     msghdr, skb);
+		/* Just release refcount here. */
+		kfree_skb(skb);
+	}
+}
+
 /* Do accounting for bytes received and hold a reference to the association
  * for each skb.
  */