tipc: Improve handling of invalid link tolerance values

Enhances TIPC link code to ignore an invalid link tolerance value
contained in an incoming LINK_PROTOCOL message, rather than
processing the value and potentially causing a divide-by-zero error.

Also add a compile-time check that catches attempts to redefine
TIPC's minimum link tolerance value in a manner that might result
in the same divide-by-zero error at run-time.
Signed-off-by: Allan Stephens <Allan.Stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

include/linux/tipc_config.h

@@ -193,6 +193,10 @@
 #define TIPC_DEF_LINK_TOL 1500
 #define TIPC_MAX_LINK_TOL 30000
 
+#if (TIPC_MIN_LINK_TOL < 16)
+#error "TIPC_MIN_LINK_TOL is too small (abort limit may be NaN)"
+#endif
+
 /*
  * Link window limits (min, default, max), in packets
  */

net/tipc/link.c

@@ -2617,6 +2617,9 @@ static void link_check_defragm_bufs(struct link *l_ptr)
 
 static void link_set_supervision_props(struct link *l_ptr, u32 tolerance)
 {
+	if ((tolerance < TIPC_MIN_LINK_TOL) || (tolerance > TIPC_MAX_LINK_TOL))
+		return;
+
 	l_ptr->tolerance = tolerance;
 	l_ptr->continuity_interval =
 		((tolerance / 4) > 500) ? 500 : tolerance / 4;