svn commit: r333603 - head/sys/netinet

[Michael Tuexen]

Author: tuexen
Date: Mon May 14 13:50:17 2018
New Revision: 333603
URL: https://svnweb.freebsd.org/changeset/base/333603

Log:
  Ensure that the MTU's used are multiple of 4.
  
  The length of SCTP packets is always a multiple of 4. Therefore,
  ensure that the MTUs used are also a multiple of 4.
  
  Thanks to Irene Ruengeler for providing an earlier version of this
  patch.
  
  MFC after:	1 week

Modified:
  head/sys/netinet/sctputil.c

Modified: head/sys/netinet/sctputil.c
==============================================================================
--- head/sys/netinet/sctputil.c	Mon May 14 07:20:34 2018	(r333602)
+++ head/sys/netinet/sctputil.c	Mon May 14 13:50:17 2018	(r333603)
@@ -758,8 +758,8 @@ sctp_stop_timers_for_shutdown(struct sctp_tcb *stcb)
 }
 
 /*
- * a list of sizes based on typical mtu's, used only if next hop size not
- * returned.
+ * A list of sizes based on typical mtu's, used only if next hop size not
+ * returned. These values MUST be multiples of 4 and MUST be ordered.
  */
 static uint32_t sctp_mtu_sizes[] = {
 	68,
@@ -768,29 +768,32 @@ static uint32_t sctp_mtu_sizes[] = {
 	512,
 	544,
 	576,
-	1006,
+	1004,
 	1492,
 	1500,
 	1536,
-	2002,
+	2000,
 	2048,
 	4352,
 	4464,
 	8166,
-	17914,
+	17912,
 	32000,
-	65535
+	65532
 };
 
 /*
- * Return the largest MTU smaller than val. If there is no
- * entry, just return val.
+ * Return the largest MTU in sctp_mtu_sizes smaller than val.
+ * If val is smaller than the minimum, just return the largest
+ * multiple of 4 smaller or equal to val.
+ * Ensure that the result is a multiple of 4.
  */
 uint32_t
 sctp_get_prev_mtu(uint32_t val)
 {
 	uint32_t i;
 
+	val &= 0x00000003;
 	if (val <= sctp_mtu_sizes[0]) {
 		return (val);
 	}
@@ -799,12 +802,16 @@ sctp_get_prev_mtu(uint32_t val)
 			break;
 		}
 	}
+	KASSERT((sctp_mtu_sizes[i - 1] & 0x00000003) == 0,
+	    ("sctp_mtu_sizes[%u] not a multiple of 4", i - 1));
 	return (sctp_mtu_sizes[i - 1]);
 }
 
 /*
- * Return the smallest MTU larger than val. If there is no
- * entry, just return val.
+ * Return the smallest MTU in sctp_mtu_sizes larger than val.
+ * If val is larger than the maximum, just return the largest multiple of 4 smaller
+ * or equal to val.
+ * Ensure that the result is a multiple of 4.
  */
 uint32_t
 sctp_get_next_mtu(uint32_t val)
@@ -812,8 +819,11 @@ sctp_get_next_mtu(uint32_t val)
 	/* select another MTU that is just bigger than this one */
 	uint32_t i;
 
+	val &= 0x00000003;
 	for (i = 0; i < (sizeof(sctp_mtu_sizes) / sizeof(uint32_t)); i++) {
 		if (val < sctp_mtu_sizes[i]) {
+			KASSERT((sctp_mtu_sizes[i] & 0x00000003) == 0,
+			    ("sctp_mtu_sizes[%u] not a multiple of 4", i));
 			return (sctp_mtu_sizes[i]);
 		}
 	}