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, 35 insertions, 12 deletions

diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index 29b81bbfc53d..222f82ffeca4 100644
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -96,6 +96,7 @@ typedef __s32 sctp_assoc_t;
 #define SCTP_AUTO_ASCONF       30
 #define SCTP_PEER_ADDR_THLDS    31
 #define SCTP_RECVRCVINFO        32
+#define SCTP_RECVNXTINFO        33
 
 /* Internal Socket Options. Some of the sctp library functions are
  * implemented using these socket options.
@@ -111,6 +112,13 @@ typedef __s32 sctp_assoc_t;
 #define SCTP_SOCKOPT_CONNECTX3  111     /* CONNECTX requests (updated) */
 #define SCTP_GET_ASSOC_STATS    112     /* Read only */
 
+/* These are bit fields for msghdr->msg_flags.  See section 5.1.  */
+/* On user space Linux, these live in <bits/socket.h> as an enum.  */
+enum sctp_msg_flags {
+        MSG_NOTIFICATION = 0x8000,
+#define MSG_NOTIFICATION MSG_NOTIFICATION
+};
+
 /* 5.3.1 SCTP Initiation Structure (SCTP_INIT)
  *
  *   This cmsghdr structure provides information for initializing new
@@ -187,6 +195,25 @@ struct sctp_rcvinfo {
         sctp_assoc_t rcv_assoc_id;
 };
 
+/* 5.3.6 SCTP Next Receive Information Structure (SCTP_NXTINFO)
+ *
+ *   This cmsghdr structure describes SCTP receive information
+ *   of the next message that will be delivered through recvmsg()
+ *   if this information is already available when delivering
+ *   the current message.
+ *
+ *   cmsg_level    cmsg_type      cmsg_data[]
+ *   ------------  ------------   -------------------
+ *   IPPROTO_SCTP  SCTP_NXTINFO   struct sctp_nxtinfo
+ */
+struct sctp_nxtinfo {
+        __u16 nxt_sid;
+        __u16 nxt_flags;
+        __u32 nxt_ppid;
+        __u32 nxt_length;
+        sctp_assoc_t nxt_assoc_id;
+};
+
 /*
  *  sinfo_flags: 16 bits (unsigned integer)
  *
@@ -194,11 +221,12 @@ struct sctp_rcvinfo {
  *   a bitwise OR of these values.
  */
 enum sctp_sinfo_flags {
-        SCTP_UNORDERED = 1,  /* Send/receive message unordered. */
-        SCTP_ADDR_OVER = 2,  /* Override the primary destination. */
-        SCTP_ABORT=4,        /* Send an ABORT message to the peer. */
-        SCTP_SACK_IMMEDIATELY = 8,      /* SACK should be sent without delay */
-        SCTP_EOF=MSG_FIN,    /* Initiate graceful shutdown process. */
+        SCTP_UNORDERED          = (1 << 0), /* Send/receive message unordered. */
+        SCTP_ADDR_OVER          = (1 << 1), /* Override the primary destination. */
+        SCTP_ABORT              = (1 << 2), /* Send an ABORT message to the peer. */
+        SCTP_SACK_IMMEDIATELY   = (1 << 3), /* SACK should be sent without delay. */
+        SCTP_NOTIFICATION       = MSG_NOTIFICATION, /* Next message is not user msg but notification. */
+        SCTP_EOF                = MSG_FIN,  /* Initiate graceful shutdown process. */
 };
 
 typedef union {
@@ -217,6 +245,8 @@ typedef enum sctp_cmsg_type {
 #define SCTP_SNDINFO    SCTP_SNDINFO
         SCTP_RCVINFO,           /* 5.3.5 SCTP Receive Information Structure */
 #define SCTP_RCVINFO    SCTP_RCVINFO
+        SCTP_NXTINFO,           /* 5.3.6 SCTP Next Receive Information Structure */
+#define SCTP_NXTINFO    SCTP_NXTINFO
 } sctp_cmsg_t;
 
 /*
@@ -844,13 +874,6 @@ struct sctp_assoc_stats {
         __u64           sas_ictrlchunks; /* Control chunks received */
 };
 
-/* These are bit fields for msghdr->msg_flags.  See section 5.1.  */
-/* On user space Linux, these live in <bits/socket.h> as an enum.  */
-enum sctp_msg_flags {
-        MSG_NOTIFICATION = 0x8000,
-#define MSG_NOTIFICATION MSG_NOTIFICATION
-};
-
 /*
  * 8.1 sctp_bindx()
  *