[SCTP] Avoid the use of constant SCTP_IP_OVERHEAD to determine the

max data size in a SCTP packet.

Calculate the overhead based on the socket's protocol family header
length.

3 files changed, 12 insertions, 11 deletions

diff --git a/include/net/sctp/constants.h b/include/net/sctp/constants.h
index 6112e85f7a9c..3a5ad29201f8 100644
--- a/include/net/sctp/constants.h
+++ b/include/net/sctp/constants.h
@@ -57,15 +57,6 @@ enum { SCTP_MAX_STREAM = 0xffff };
 enum { SCTP_DEFAULT_OUTSTREAMS = 10 };
 enum { SCTP_DEFAULT_INSTREAMS = SCTP_MAX_STREAM };
 
-/* Define the amount of space to reserve for SCTP, IP, LL.
- * There is a little bit of waste that we are always allocating
- * for ipv6 headers, but this seems worth the simplicity.
- */
-
-#define SCTP_IP_OVERHEAD ((sizeof(struct sctphdr)\
-                          + sizeof(struct ipv6hdr)\
-                          + MAX_HEADER))
-
 /* Since CIDs are sparse, we need all four of the following
  * symbols.  CIDs are dense through SCTP_CID_BASE_MAX.
  */
diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index 6a6c6641e446..ee5e38a37d00 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -437,12 +437,15 @@ static inline __s32 sctp_jitter(__u32 rto)
 static inline int sctp_frag_point(const struct sctp_opt *sp, int pmtu)
 {
 	int frag = pmtu;
-	frag -= SCTP_IP_OVERHEAD + sizeof(struct sctp_data_chunk);
-	frag -= sizeof(struct sctp_sack_chunk);
+
+	frag -= sp->pf->af->net_header_len;
+	frag -= sizeof(struct sctphdr) + sizeof(struct sctp_data_chunk);
 
 	if (sp->user_frag)
 		frag = min_t(int, frag, sp->user_frag);
 
+	frag = min_t(int, frag, SCTP_MAX_CHUNK_LEN);
+
 	return frag;
 }
 
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index a9f8c029361e..1731d02dc837 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -667,6 +667,9 @@ struct sctp_packet {
 
 	/* This contains the payload chunks.  */
 	struct sk_buff_head chunks;
+
+	/* This is the overhead of the sctp and ip headers. */
+	size_t overhead;
 	/* This is the total size of all chunks INCLUDING padding.  */
 	size_t size;
 
@@ -721,6 +724,10 @@ sctp_outq_ohandler_t	     sctp_packet_transmit_chunk;
 sctp_outq_ohandler_force_t   sctp_packet_transmit;
 void sctp_packet_free(struct sctp_packet *);
 
+static inline int sctp_packet_empty(struct sctp_packet *packet)
+{
+	return (packet->size == packet->overhead);
+}
 
 /* This represents a remote transport address.
  * For local transport addresses, we just use union sctp_addr.