net: codel: Avoid undefined behavior from signed overflow

[linux-2.6-microblaze.git] / include / net / codel.h

diff --git a/include/net/codel.h b/include/net/codel.h
index 389cf62..3b04ff5 100644 (file)
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -72,10 +72,21 @@ static inline codel_time_t codel_get_time(void)
        return ns >> CODEL_SHIFT;
 }
 
-#define codel_time_after(a, b)         ((s32)(a) - (s32)(b) > 0)
-#define codel_time_after_eq(a, b)      ((s32)(a) - (s32)(b) >= 0)
-#define codel_time_before(a, b)                ((s32)(a) - (s32)(b) < 0)
-#define codel_time_before_eq(a, b)     ((s32)(a) - (s32)(b) <= 0)
+/* Dealing with timer wrapping, according to RFC 1982, as desc in wikipedia:
+ *  https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
+ * codel_time_after(a,b) returns true if the time a is after time b.
+ */
+#define codel_time_after(a, b)                                         \
+       (typecheck(codel_time_t, a) &&                                  \
+        typecheck(codel_time_t, b) &&                                  \
+        ((s32)((a) - (b)) > 0))
+#define codel_time_before(a, b)        codel_time_after(b, a)
+
+#define codel_time_after_eq(a, b)                                      \
+       (typecheck(codel_time_t, a) &&                                  \
+        typecheck(codel_time_t, b) &&                                  \
+        ((s32)((a) - (b)) >= 0))
+#define codel_time_before_eq(a, b)     codel_time_after_eq(b, a)
 
 /* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
 struct codel_skb_cb {