1 files changed, 23 insertions, 9 deletions

diff --git a/net/sctp/chunk.c b/net/sctp/chunk.c
index 1748ef90950c..9292294dbc12 100644
--- a/net/sctp/chunk.c
+++ b/net/sctp/chunk.c
@@ -158,6 +158,7 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 {
         int max, whole, i, offset, over, err;
         int len, first_len;
+        int max_data;
         struct sctp_chunk *chunk;
         struct sctp_datamsg *msg;
         struct list_head *pos, *temp;
@@ -179,8 +180,14 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
                                   __func__, msg, msg->expires_at, jiffies);
         }
 
-        max = asoc->frag_point;
+        /* This is the biggest possible DATA chunk that can fit into
+         * the packet
+         */
+        max_data = asoc->pathmtu -
+                sctp_sk(asoc->base.sk)->pf->af->net_header_len -
+                sizeof(struct sctphdr) - sizeof(struct sctp_data_chunk);
 
+        max = asoc->frag_point;
         /* If the the peer requested that we authenticate DATA chunks
          * we need to accound for bundling of the AUTH chunks along with
          * DATA.
@@ -189,23 +196,30 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
                 struct sctp_hmac *hmac_desc = sctp_auth_asoc_get_hmac(asoc);
 
                 if (hmac_desc)
-                        max -= WORD_ROUND(sizeof(sctp_auth_chunk_t) +
+                        max_data -= WORD_ROUND(sizeof(sctp_auth_chunk_t) +
                                             hmac_desc->hmac_len);
         }
 
+        /* Now, check if we need to reduce our max */
+        if (max > max_data)
+                max = max_data;
+
         whole = 0;
         first_len = max;
 
         /* Encourage Cookie-ECHO bundling. */
         if (asoc->state < SCTP_STATE_COOKIE_ECHOED) {
-                whole = msg_len / (max - SCTP_ARBITRARY_COOKIE_ECHO_LEN);
+                max_data -= SCTP_ARBITRARY_COOKIE_ECHO_LEN;
 
-                /* Account for the DATA to be bundled with the COOKIE-ECHO. */
-                if (whole) {
-                        first_len = max - SCTP_ARBITRARY_COOKIE_ECHO_LEN;
-                        msg_len -= first_len;
-                        whole = 1;
-                }
+                /* This is the biggesr first_len we can have */
+                if (first_len > max_data)
+                        first_len = max_data;
+        }
+
+        /* Account for a different sized first fragment */
+        if (msg_len >= first_len) {
+                msg_len -= first_len;
+                whole = 1;
         }
 
         /* How many full sized?  How many bytes leftover? */