net: sctp: implement rfc6458, 5.3.4. SCTP_SNDINFO cmsg support

This patch implements section 5.3.4. of RFC6458, that is, support
for 'SCTP Send Information Structure' (SCTP_SNDINFO) which can be
placed into ancillary data cmsghdr structure for sendmsg() calls.

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

  struct sctp_sndinfo {
    uint16_t snd_sid;
    uint16_t snd_flags;
    uint32_t snd_ppid;
    uint32_t snd_context;
    sctp_assoc_t snd_assoc_id;
  };

... and supplied under cmsg_level IPPROTO_SCTP, cmsg_type
SCTP_SNDINFO, while cmsg_data[] contains struct sctp_sndinfo.
An sctp_sndinfo item always corresponds to the data in msg_iov.

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, 20 insertions, 2 deletions

diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index 266022a2be4a..a387761f7e02 100644
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -154,6 +154,22 @@ struct sctp_sndrcvinfo {
         sctp_assoc_t sinfo_assoc_id;
 };
 
+/* 5.3.4 SCTP Send Information Structure (SCTP_SNDINFO)
+ *
+ *   This cmsghdr structure specifies SCTP options for sendmsg().
+ *
+ *   cmsg_level    cmsg_type      cmsg_data[]
+ *   ------------  ------------   -------------------
+ *   IPPROTO_SCTP  SCTP_SNDINFO   struct sctp_sndinfo
+ */
+struct sctp_sndinfo {
+        __u16 snd_sid;
+        __u16 snd_flags;
+        __u32 snd_ppid;
+        __u32 snd_context;
+        sctp_assoc_t snd_assoc_id;
+};
+
 /*
  *  sinfo_flags: 16 bits (unsigned integer)
  *
@@ -177,10 +193,12 @@ typedef union {
 
 /* These are cmsg_types.  */
 typedef enum sctp_cmsg_type {
-        SCTP_INIT,              /* 5.2.1 SCTP Initiation Structure */
+        SCTP_INIT,              /* 5.2.1 SCTP Initiation Structure */
 #define SCTP_INIT       SCTP_INIT
-        SCTP_SNDRCV,            /* 5.2.2 SCTP Header Information Structure */
+        SCTP_SNDRCV,            /* 5.2.2 SCTP Header Information Structure */
 #define SCTP_SNDRCV     SCTP_SNDRCV
+        SCTP_SNDINFO,           /* 5.3.4 SCTP Send Information Structure */
+#define SCTP_SNDINFO    SCTP_SNDINFO
 } sctp_cmsg_t;
 
 /*