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>

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);
 

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;

net/sctp/associola.c

@@ -112,6 +112,7 @@ static struct sctp_association *sctp_association_init(struct sctp_association *a
 	asoc->cookie_life.tv_usec = (sp->assocparams.sasoc_cookie_life % 1000)
 					* 1000;
 	asoc->frag_point = 0;
+	asoc->user_frag = sp->user_frag;
 
 	/* Set the association max_retrans and RTO values from the
 	 * socket values.
@@ -674,7 +675,7 @@ struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
 			  "%d\n", asoc, asoc->pathmtu);
 	peer->pmtu_pending = 0;
 
-	asoc->frag_point = sctp_frag_point(sp, asoc->pathmtu);
+	asoc->frag_point = sctp_frag_point(asoc, asoc->pathmtu);
 
 	/* The asoc->peer.port might not be meaningful yet, but
 	 * initialize the packet structure anyway.
@@ -1330,9 +1331,8 @@ void sctp_assoc_sync_pmtu(struct sctp_association *asoc)
 	}
 
 	if (pmtu) {
-		struct sctp_sock *sp = sctp_sk(asoc->base.sk);
 		asoc->pathmtu = pmtu;
-		asoc->frag_point = sctp_frag_point(sp, pmtu);
+		asoc->frag_point = sctp_frag_point(asoc, pmtu);
 	}
 
 	SCTP_DEBUG_PRINTK("%s: asoc:%p, pmtu:%d, frag_point:%d\n",

net/sctp/socket.c

@@ -2243,7 +2243,7 @@ static int sctp_apply_peer_addr_params(struct sctp_paddrparams *params,
 			sctp_assoc_sync_pmtu(asoc);
 		} else if (asoc) {
 			asoc->pathmtu = params->spp_pathmtu;
-			sctp_frag_point(sp, params->spp_pathmtu);
+			sctp_frag_point(asoc, params->spp_pathmtu);
 		} else {
 			sp->pathmtu = params->spp_pathmtu;
 		}
@@ -2880,15 +2880,10 @@ static int sctp_setsockopt_maxseg(struct sock *sk, char __user *optval, int optl
 			val -= sizeof(struct sctphdr) +
 					sizeof(struct sctp_data_chunk);
 		}
-
-		asoc->frag_point = val;
+		asoc->user_frag = val;
+		asoc->frag_point = sctp_frag_point(asoc, asoc->pathmtu);
 	} else {
 		sp->user_frag = val;
-
-		/* Update the frag_point of the existing associations. */
-		list_for_each_entry(asoc, &(sp->ep->asocs), asocs) {
-			asoc->frag_point = sctp_frag_point(sp, asoc->pathmtu);
-		}
 	}
 
 	return 0;