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>

3 files changed, 4 insertions, 7 deletions

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index c2035c96a2ee..90c1cccd164d 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -109,6 +109,7 @@ void sctp_copy_sock(struct sock *newsk, struct sock *sk,
                     struct sctp_association *asoc);
 extern struct percpu_counter sctp_sockets_allocated;
 int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);
+struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int, int *);
 
 /*
  * sctp/primitive.c
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 11d5df015370..7741d1b66967 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -218,6 +218,7 @@ struct sctp_sock {
         __u32 adaptation_ind;
         __u32 pd_point;
         __u8 recvrcvinfo;
+        __u8 recvnxtinfo;
 
         atomic_t pd_mode;
         /* Receive to here while partial delivery is in effect. */
diff --git a/include/net/sctp/ulpevent.h b/include/net/sctp/ulpevent.h
index e8095f973e94..cccdcfd14973 100644
--- a/include/net/sctp/ulpevent.h
+++ b/include/net/sctp/ulpevent.h
@@ -132,6 +132,8 @@ void sctp_ulpevent_read_sndrcvinfo(const struct sctp_ulpevent *event,
                                    struct msghdr *);
 void sctp_ulpevent_read_rcvinfo(const struct sctp_ulpevent *event,
                                 struct msghdr *);
+void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
+                                struct msghdr *, struct sock *sk);
 
 __u16 sctp_ulpevent_get_notification_type(const struct sctp_ulpevent *event);
 
@@ -158,10 +160,3 @@ static inline int sctp_ulpevent_is_enabled(const struct sctp_ulpevent *event,
 }
 
 #endif /* __sctp_ulpevent_h__ */
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