net: sctp: implement rfc6458, 5.3.5. SCTP_RCVINFO cmsg support

This patch implements section 5.3.5. of RFC6458, that is, support
for 'SCTP Receive Information Structure' (SCTP_RCVINFO) which is
placed into ancillary data cmsghdr structure for each recvmsg()
call.

This option can be enabled/disabled via setsockopt(2) on SOL_SCTP
level by setting an int value with 1/0 for SCTP_RECVRCVINFO in user
space applications as per RFC6458, section 8.1.29.

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

  struct sctp_rcvinfo {
    uint16_t rcv_sid;
    uint16_t rcv_ssn;
    uint16_t rcv_flags;
    <-- 2 bytes hole  -->
    uint32_t rcv_ppid;
    uint32_t rcv_tsn;
    uint32_t rcv_cumtsn;
    uint32_t rcv_context;
    sctp_assoc_t rcv_assoc_id;
  };

... and provided under cmsg_level IPPROTO_SCTP, cmsg_type
SCTP_RCVINFO, while cmsg_data[] contains struct sctp_rcvinfo.
An sctp_rcvinfo 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>

2 files changed, 73 insertions, 1 deletions

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index d61729e99856..9c193887c5cd 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -2112,9 +2112,13 @@ static int sctp_recvmsg(struct kiocb *iocb, struct sock *sk,
                 sp->pf->skb_msgname(skb, msg->msg_name, addr_len);
         }
 
+        /* Check if we allow SCTP_RCVINFO. */
+        if (sp->recvrcvinfo)
+                sctp_ulpevent_read_rcvinfo(event, msg);
         /* Check if we allow SCTP_SNDRCVINFO. */
         if (sp->subscribe.sctp_data_io_event)
                 sctp_ulpevent_read_sndrcvinfo(event, msg);
+
 #if 0
         /* FIXME: we should be calling IP/IPv6 layers.  */
         if (sk->sk_protinfo.af_inet.cmsg_flags)
@@ -3541,7 +3545,6 @@ static int sctp_setsockopt_auto_asconf(struct sock *sk, char __user *optval,
         return 0;
 }
 
-
 /*
  * SCTP_PEER_ADDR_THLDS
  *
@@ -3592,6 +3595,22 @@ static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
         return 0;
 }
 
+static int sctp_setsockopt_recvrcvinfo(struct sock *sk,
+                                       char __user *optval,
+                                       unsigned int optlen)
+{
+        int val;
+
+        if (optlen < sizeof(int))
+                return -EINVAL;
+        if (get_user(val, (int __user *) optval))
+                return -EFAULT;
+
+        sctp_sk(sk)->recvrcvinfo = (val == 0) ? 0 : 1;
+
+        return 0;
+}
+
 /* API 6.2 setsockopt(), getsockopt()
  *
  * Applications use setsockopt() and getsockopt() to set or retrieve
@@ -3743,6 +3762,9 @@ static int sctp_setsockopt(struct sock *sk, int level, int optname,
         case SCTP_PEER_ADDR_THLDS:
                 retval = sctp_setsockopt_paddr_thresholds(sk, optval, optlen);
                 break;
+        case SCTP_RECVRCVINFO:
+                retval = sctp_setsockopt_recvrcvinfo(sk, optval, optlen);
+                break;
         default:
                 retval = -ENOPROTOOPT;
                 break;
@@ -3989,6 +4011,8 @@ static int sctp_init_sock(struct sock *sk)
         /* Enable Nagle algorithm by default.  */
         sp->nodelay           = 0;
 
+        sp->recvrcvinfo = 0;
+
         /* Enable by default. */
         sp->v4mapped          = 1;
 
@@ -5770,6 +5794,26 @@ static int sctp_getsockopt_assoc_stats(struct sock *sk, int len,
         return 0;
 }
 
+static int sctp_getsockopt_recvrcvinfo(struct sock *sk, int len,
+                                       char __user *optval,
+                                       int __user *optlen)
+{
+        int val = 0;
+
+        if (len < sizeof(int))
+                return -EINVAL;
+
+        len = sizeof(int);
+        if (sctp_sk(sk)->recvrcvinfo)
+                val = 1;
+        if (put_user(len, optlen))
+                return -EFAULT;
+        if (copy_to_user(optval, &val, len))
+                return -EFAULT;
+
+        return 0;
+}
+
 static int sctp_getsockopt(struct sock *sk, int level, int optname,
                            char __user *optval, int __user *optlen)
 {
@@ -5913,6 +5957,9 @@ static int sctp_getsockopt(struct sock *sk, int level, int optname,
         case SCTP_GET_ASSOC_STATS:
                 retval = sctp_getsockopt_assoc_stats(sk, len, optval, optlen);
                 break;
+        case SCTP_RECVRCVINFO:
+                retval = sctp_getsockopt_recvrcvinfo(sk, len, optval, optlen);
+                break;
         default:
                 retval = -ENOPROTOOPT;
                 break;
diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
index b6842fdb53d4..b31f365f18ab 100644
--- a/net/sctp/ulpevent.c
+++ b/net/sctp/ulpevent.c
@@ -886,6 +886,31 @@ void sctp_ulpevent_read_sndrcvinfo(const struct sctp_ulpevent *event,
                  sizeof(sinfo), &sinfo);
 }
 
+/* RFC6458, Section 5.3.5 SCTP Receive Information Structure
+ * (SCTP_SNDRCV)
+ */
+void sctp_ulpevent_read_rcvinfo(const struct sctp_ulpevent *event,
+                                struct msghdr *msghdr)
+{
+        struct sctp_rcvinfo rinfo;
+
+        if (sctp_ulpevent_is_notification(event))
+                return;
+
+        memset(&rinfo, 0, sizeof(struct sctp_rcvinfo));
+        rinfo.rcv_sid = event->stream;
+        rinfo.rcv_ssn = event->ssn;
+        rinfo.rcv_ppid = event->ppid;
+        rinfo.rcv_flags = event->flags;
+        rinfo.rcv_tsn = event->tsn;
+        rinfo.rcv_cumtsn = event->cumtsn;
+        rinfo.rcv_assoc_id = sctp_assoc2id(event->asoc);
+        rinfo.rcv_context = event->asoc->default_rcv_context;
+
+        put_cmsg(msghdr, IPPROTO_SCTP, SCTP_RCVINFO,
+                 sizeof(rinfo), &rinfo);
+}
+
 /* Do accounting for bytes received and hold a reference to the association
  * for each skb.
  */