sctp: Fix SCTP_MAXSEG socket option to comply to spec.

We had a bug that we never stored the user-defined value for
MAXSEG when setting the value on an association.  Thus future
PMTU events ended up re-writing the frag point and increasing
it past user limit.  Additionally, when setting the option on
the socket/endpoint, we effect all current associations, which
is against spec.

Now, we store the user 'maxseg' value along with the computed
'frag_point'.  We inherit 'maxseg' from the socket at association
creation and use it as an upper limit for 'frag_point' when its
set.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>

2 files changed, 5 insertions, 3 deletions

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index d16a304cbed4..8a6d5297de16 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -486,15 +486,16 @@ static inline __s32 sctp_jitter(__u32 rto)
 }
 
 /* Break down data chunks at this point.  */
-static inline int sctp_frag_point(const struct sctp_sock *sp, int pmtu)
+static inline int sctp_frag_point(const struct sctp_association *asoc, int pmtu)
 {
+        struct sctp_sock *sp = sctp_sk(asoc->base.sk);
         int frag = pmtu;
 
         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);
+        if (asoc->user_frag)
+                frag = min_t(int, frag, asoc->user_frag);
 
         frag = min_t(int, frag, SCTP_MAX_CHUNK_LEN);
 
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index df4c6321996d..b10612810f56 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1763,6 +1763,7 @@ struct sctp_association {
 
         /* The message size at which SCTP fragmentation will occur. */
         __u32 frag_point;
+        __u32 user_frag;
 
         /* Counter used to count INIT errors. */
         int init_err_counter;