broken by commit 
5e739d1752aca4e8f3e794d431503bfca3162df4; AFAICS should
be -stable fodder as well...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Aced-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
                if (sctp_addip_enable) {
                        auth_chunks->chunks[0] = SCTP_CID_ASCONF;
                        auth_chunks->chunks[1] = SCTP_CID_ASCONF_ACK;
-                       auth_chunks->param_hdr.length += htons(2);
+                       auth_chunks->param_hdr.length =
+                                       htons(sizeof(sctp_paramhdr_t) + 2);
                }
        }