[CCID3] Avoid unsigned integer overflows in usecs_div

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

net/dccp/ccids/ccid3.c

@@ -43,12 +43,22 @@
 #include "ccid3.h"
 
 /*
- * Reason for maths with 10 here is to avoid 32 bit overflow when a is big.
+ * Reason for maths here is to avoid 32 bit overflow when a is big.
+ * With this we get close to the limit.
  */
 static inline u32 usecs_div(const u32 a, const u32 b)
 {
-	const u32 tmp = a * (USEC_PER_SEC / 10);
-	return b > 20 ? tmp / (b / 10) : tmp;
+	const u32 div = a < (UINT_MAX / (USEC_PER_SEC /    10)) ?    10 :
+			a < (UINT_MAX / (USEC_PER_SEC /    50)) ?    50 :
+			a < (UINT_MAX / (USEC_PER_SEC /   100)) ?   100 :
+			a < (UINT_MAX / (USEC_PER_SEC /   500)) ?   500 :
+			a < (UINT_MAX / (USEC_PER_SEC /  1000)) ?  1000 :
+			a < (UINT_MAX / (USEC_PER_SEC /  5000)) ?  5000 :
+			a < (UINT_MAX / (USEC_PER_SEC / 10000)) ? 10000 :
+			a < (UINT_MAX / (USEC_PER_SEC / 50000)) ? 50000 :
+								 100000;
+	const u32 tmp = a * (USEC_PER_SEC / div);
+	return (b >= 2 * div) ? tmp / (b / div) : tmp;
 }
 
 static int ccid3_debug;