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, 57 insertions, 20 deletions

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 429899689408..d61729e99856 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1602,12 +1602,13 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
         struct sctp_initmsg *sinit;
         sctp_assoc_t associd = 0;
         sctp_cmsgs_t cmsgs = { NULL };
-        int err;
         sctp_scope_t scope;
-        long timeo;
-        __u16 sinfo_flags = 0;
+        bool fill_sinfo_ttl = false;
         struct sctp_datamsg *datamsg;
         int msg_flags = msg->msg_flags;
+        __u16 sinfo_flags = 0;
+        long timeo;
+        int err;
 
         err = 0;
         sp = sctp_sk(sk);
@@ -1648,10 +1649,21 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
                 msg_name = msg->msg_name;
         }
 
-        sinfo = cmsgs.info;
         sinit = cmsgs.init;
+        if (cmsgs.sinfo != NULL) {
+                memset(&default_sinfo, 0, sizeof(default_sinfo));
+                default_sinfo.sinfo_stream = cmsgs.sinfo->snd_sid;
+                default_sinfo.sinfo_flags = cmsgs.sinfo->snd_flags;
+                default_sinfo.sinfo_ppid = cmsgs.sinfo->snd_ppid;
+                default_sinfo.sinfo_context = cmsgs.sinfo->snd_context;
+                default_sinfo.sinfo_assoc_id = cmsgs.sinfo->snd_assoc_id;
 
-        /* Did the user specify SNDRCVINFO?  */
+                sinfo = &default_sinfo;
+                fill_sinfo_ttl = true;
+        } else {
+                sinfo = cmsgs.srinfo;
+        }
+        /* Did the user specify SNDINFO/SNDRCVINFO? */
         if (sinfo) {
                 sinfo_flags = sinfo->sinfo_flags;
                 associd = sinfo->sinfo_assoc_id;
@@ -1858,8 +1870,8 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
         pr_debug("%s: we have a valid association\n", __func__);
 
         if (!sinfo) {
-                /* If the user didn't specify SNDRCVINFO, make up one with
-                 * some defaults.
+                /* If the user didn't specify SNDINFO/SNDRCVINFO, make up
+                 * one with some defaults.
                  */
                 memset(&default_sinfo, 0, sizeof(default_sinfo));
                 default_sinfo.sinfo_stream = asoc->default_stream;
@@ -1868,7 +1880,13 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
                 default_sinfo.sinfo_context = asoc->default_context;
                 default_sinfo.sinfo_timetolive = asoc->default_timetolive;
                 default_sinfo.sinfo_assoc_id = sctp_assoc2id(asoc);
+
                 sinfo = &default_sinfo;
+        } else if (fill_sinfo_ttl) {
+                /* In case SNDINFO was specified, we still need to fill
+                 * it with a default ttl from the assoc here.
+                 */
+                sinfo->sinfo_timetolive = asoc->default_timetolive;
         }
 
         /* API 7.1.7, the sndbuf size per association bounds the
@@ -6390,8 +6408,7 @@ static int sctp_msghdr_parse(const struct msghdr *msg, sctp_cmsgs_t *cmsgs)
         struct cmsghdr *cmsg;
         struct msghdr *my_msg = (struct msghdr *)msg;
 
-        for (cmsg = CMSG_FIRSTHDR(msg);
-             cmsg != NULL;
+        for (cmsg = CMSG_FIRSTHDR(msg); cmsg != NULL;
              cmsg = CMSG_NXTHDR(my_msg, cmsg)) {
                 if (!CMSG_OK(my_msg, cmsg))
                         return -EINVAL;
@@ -6404,7 +6421,7 @@ static int sctp_msghdr_parse(const struct msghdr *msg, sctp_cmsgs_t *cmsgs)
                 switch (cmsg->cmsg_type) {
                 case SCTP_INIT:
                         /* SCTP Socket API Extension
-                         * 5.2.1 SCTP Initiation Structure (SCTP_INIT)
+                         * 5.3.1 SCTP Initiation Structure (SCTP_INIT)
                          *
                          * This cmsghdr structure provides information for
                          * initializing new SCTP associations with sendmsg().
@@ -6416,15 +6433,15 @@ static int sctp_msghdr_parse(const struct msghdr *msg, sctp_cmsgs_t *cmsgs)
                          * ------------  ------------   ----------------------
                          * IPPROTO_SCTP  SCTP_INIT      struct sctp_initmsg
                          */
-                        if (cmsg->cmsg_len !=
-                            CMSG_LEN(sizeof(struct sctp_initmsg)))
+                        if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct sctp_initmsg)))
                                 return -EINVAL;
-                        cmsgs->init = (struct sctp_initmsg *)CMSG_DATA(cmsg);
+
+                        cmsgs->init = CMSG_DATA(cmsg);
                         break;
 
                 case SCTP_SNDRCV:
                         /* SCTP Socket API Extension
-                         * 5.2.2 SCTP Header Information Structure(SCTP_SNDRCV)
+                         * 5.3.2 SCTP Header Information Structure(SCTP_SNDRCV)
                          *
                          * This cmsghdr structure specifies SCTP options for
                          * sendmsg() and describes SCTP header information
@@ -6434,24 +6451,44 @@ static int sctp_msghdr_parse(const struct msghdr *msg, sctp_cmsgs_t *cmsgs)
                          * ------------  ------------   ----------------------
                          * IPPROTO_SCTP  SCTP_SNDRCV    struct sctp_sndrcvinfo
                          */
-                        if (cmsg->cmsg_len !=
-                            CMSG_LEN(sizeof(struct sctp_sndrcvinfo)))
+                        if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct sctp_sndrcvinfo)))
                                 return -EINVAL;
 
-                        cmsgs->info =
-                                (struct sctp_sndrcvinfo *)CMSG_DATA(cmsg);
+                        cmsgs->srinfo = CMSG_DATA(cmsg);
 
-                        /* Minimally, validate the sinfo_flags. */
-                        if (cmsgs->info->sinfo_flags &
+                        if (cmsgs->srinfo->sinfo_flags &
                             ~(SCTP_UNORDERED | SCTP_ADDR_OVER |
                               SCTP_ABORT | SCTP_EOF))
                                 return -EINVAL;
                         break;
 
+                case SCTP_SNDINFO:
+                        /* SCTP Socket API Extension
+                         * 5.3.4 SCTP Send Information Structure (SCTP_SNDINFO)
+                         *
+                         * This cmsghdr structure specifies SCTP options for
+                         * sendmsg(). This structure and SCTP_RCVINFO replaces
+                         * SCTP_SNDRCV which has been deprecated.
+                         *
+                         * cmsg_level    cmsg_type      cmsg_data[]
+                         * ------------  ------------   ---------------------
+                         * IPPROTO_SCTP  SCTP_SNDINFO    struct sctp_sndinfo
+                         */
+                        if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct sctp_sndinfo)))
+                                return -EINVAL;
+
+                        cmsgs->sinfo = CMSG_DATA(cmsg);
+
+                        if (cmsgs->sinfo->snd_flags &
+                            ~(SCTP_UNORDERED | SCTP_ADDR_OVER |
+                              SCTP_ABORT | SCTP_EOF))
+                                return -EINVAL;
+                        break;
                 default:
                         return -EINVAL;
                 }
         }
+
         return 0;
 }