Merge branch 'sctp'

Daniel Borkmann says:

====================
Misc SCTP updates

Daniel Borkmann (2):
  net: sctp: improve timer slack calculation for transport HBs
  net: sctp: only warn in proc_sctp_do_alpha_beta if write
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Neil Horman <nhorman@tuxdriver.com>

include/net/sctp/sctp.h

@@ -388,27 +388,6 @@ static inline int sctp_list_single_entry(struct list_head *head)
 	return (head->next != head) && (head->next == head->prev);
 }
 
-/* Generate a random jitter in the range of -50% ~ +50% of input RTO. */
-static inline __s32 sctp_jitter(__u32 rto)
-{
-	static __u32 sctp_rand;
-	__s32 ret;
-
-	/* Avoid divide by zero. */
-	if (!rto)
-		rto = 1;
-
-	sctp_rand += jiffies;
-	sctp_rand ^= (sctp_rand << 12);
-	sctp_rand ^= (sctp_rand >> 20);
-
-	/* Choose random number from 0 to rto, then move to -50% ~ +50%
-	 * of rto.
-	 */
-	ret = sctp_rand % rto - (rto >> 1);
-	return ret;
-}
-
 /* Break down data chunks at this point.  */
 static inline int sctp_frag_point(const struct sctp_association *asoc, int pmtu)
 {

net/sctp/sysctl.c

@@ -424,6 +424,7 @@ static int proc_sctp_do_alpha_beta(struct ctl_table *ctl, int write,
 				   void __user *buffer, size_t *lenp,
 				   loff_t *ppos)
 {
+	if (write)
 		pr_warn_once("Changing rto_alpha or rto_beta may lead to "
 			     "suboptimal rtt/srtt estimations!\n");
 

net/sctp/transport.c

@@ -594,15 +594,16 @@ void sctp_transport_burst_reset(struct sctp_transport *t)
 }
 
 /* What is the next timeout value for this transport? */
-unsigned long sctp_transport_timeout(struct sctp_transport *t)
+unsigned long sctp_transport_timeout(struct sctp_transport *trans)
 {
-	unsigned long timeout;
-	timeout = t->rto + sctp_jitter(t->rto);
-	if ((t->state != SCTP_UNCONFIRMED) &&
-	    (t->state != SCTP_PF))
-		timeout += t->hbinterval;
-	timeout += jiffies;
-	return timeout;
+	/* RTO + timer slack +/- 50% of RTO */
+	unsigned long timeout = (trans->rto >> 1) + prandom_u32_max(trans->rto);
+
+	if (trans->state != SCTP_UNCONFIRMED &&
+	    trans->state != SCTP_PF)
+		timeout += trans->hbinterval;
+
+	return timeout + jiffies;
 }
 
 /* Reset transport variables to their initial values */