app-layer-htp, stream-tcp: prevent modulo bias in RandomGetWrap()

RAND_MAX is not guaranteed to be a divisor of ULONG_MAX, so take the
necessary precautions to get unbiased random numbers. Although the
bias might be negligible, it's not advisable to rely on it.

src/app-layer-htp.c

@@ -2215,9 +2215,13 @@ static void HTPConfigSetDefaultsPhase1(HTPCfgRec *cfg_prec)
  */
 static int RandomGetWrap(void)
 {
-    long int r = RandomGet();
+    unsigned long r;
-    int r_int = r % (long int)RAND_MAX;
+
-    return abs(r_int);
+    do {
+        r = RandomGet();
+    } while(r >= ULONG_MAX - (ULONG_MAX % RAND_MAX));
+
+    return r % RAND_MAX;
 }
 
 /*

src/stream-tcp.c

@@ -344,9 +344,13 @@ int StreamTcpInlineDropInvalid(void)
  */
 static int RandomGetWrap(void)
 {
-    long int r = RandomGet();
+    unsigned long r;
-    int r_int = r % (long int)RAND_MAX;
+
-    return abs(r_int);
+    do {
+        r = RandomGet();
+    } while(r >= ULONG_MAX - (ULONG_MAX % RAND_MAX));
+
+    return r % RAND_MAX;
 }
 
 /** \brief          To initialize the stream global configuration data