Fixed random numbers for port, interface and server selection.

Removed very small bias.
Also some lint fixes.



git-svn-id: file:///svn/unbound/trunk@2049 be551aaa-1e26-0410-a405-d3ace91eadb9

daemon/daemon.c

@@ -292,7 +292,7 @@ int daemon_get_shufport(struct daemon* daemon, int* shufport)
         /* Knuth shuffle */
 	n = avail;
 	while(--n > 0) {
-		k = ub_random(daemon->rand) % (n+1); /* 0<= k<= n */
+		k = ub_random_max(daemon->rand, n+1); /* 0<= k<= n */
 		temp = shufport[k];
 		shufport[k] = shufport[n];
 		shufport[n] = temp;

doc/Changelog

@@ -1,3 +1,7 @@
+18 March 2010: Wouter
+	- Fixed random numbers for port, interface and server selection.
+	  Removed very small bias.
+
 16 March 2010: Wouter
 	- Fix interface-automatic for OpenBSD: msg.controllen was too small,
 	  also assertions on ancillary data buffer.

iterator/iter_utils.c

@@ -350,9 +350,9 @@ iter_server_selection(struct iter_env* iter_env,
 
 	/* randomly select a target from the list */
 	log_assert(num > 1);
-	/* we do not need secure random numbers here, but
-	 * we do need it to be threadsafe, so we use this */
-	sel = ub_random(env->rnd) % num; 
+	/* grab secure random number, to pick unexpected server.
+	 * also we need it to be threadsafe. */
+	sel = ub_random_max(env->rnd, num); 
 	a = dp->result_list;
 	prev = NULL;
 	while(sel > 0 && a) {
@@ -418,7 +418,7 @@ iter_ns_probability(struct ub_randstate* rnd, int n, int m)
 		return 1;
 	/* we do not need secure random numbers here, but
 	 * we do need it to be threadsafe, so we use this */
-	sel = ub_random(rnd) % m; 
+	sel = ub_random_max(rnd, m); 
 	return (sel < n);
 }
 

pythonmod/pythonmod.c

@@ -57,6 +57,8 @@
 
 #ifdef S_SPLINT_S
 typedef struct PyObject PyObject;
+typedef struct PyThreadState PyThreadState;
+typedef void* PyGILState_STATE;
 #endif
 
 /**

services/outside_network.c

@@ -809,9 +809,9 @@ select_ifport(struct outside_network* outnet, struct pending* pend,
 	log_assert(outnet->unused_fds);
 	tries = 0;
 	while(1) {
-		my_if = ub_random(outnet->rnd) % num_if;
+		my_if = ub_random_max(outnet->rnd, num_if);
 		pif = &ifs[my_if];
-		my_port = ub_random(outnet->rnd) % pif->avail_total;
+		my_port = ub_random_max(outnet->rnd, pif->avail_total);
 		if(my_port < pif->inuse) {
 			/* port already open */
 			pend->pc = pif->out[my_port];

testcode/unitmain.c

@@ -447,10 +447,12 @@ static void
 rnd_test()
 {
 	struct ub_randstate* r;
-	int num = 100, i;
-	long int a[100];
+	int num = 1000, i;
+	long int a[1000];
+	unsigned int seed = (unsigned)time(NULL);
 	unit_show_feature("ub_random");
-	unit_assert( (r = ub_initstate((unsigned)time(NULL), NULL)) );
+	printf("ub_random seed is %u\n", seed);
+	unit_assert( (r = ub_initstate(seed, NULL)) );
 	for(i=0; i<num; i++) {
 		a[i] = ub_random(r);
 		unit_assert(a[i] >= 0);
@@ -460,6 +462,14 @@ rnd_test()
 				a[i] != a[i-3] || a[i] != a[i-4] ||
 				a[i] != a[i-5] || a[i] != a[i-6]);
 	}
+	a[0] = ub_random_max(r, 1);
+	unit_assert(a[0] >= 0 && a[0] < 1);
+	a[0] = ub_random_max(r, 10000);
+	unit_assert(a[0] >= 0 && a[0] < 10000);
+	for(i=0; i<num; i++) {
+		a[i] = ub_random_max(r, 10);
+		unit_assert(a[i] >= 0 && a[i] < 10);
+	}
 	ub_randfree(r);
 }
 

util/random.c

@@ -177,6 +177,18 @@ ub_random(struct ub_randstate* s)
 	return (long int)((r) % (((unsigned)MAX_VALUE + 1)));
 }
 
+long int
+ub_random_max(struct ub_randstate* state, long int x)
+{
+	/* make sure we fetch in a range that is divisible by x. ignore
+	 * values from d .. MAX_VALUE, instead draw a new number */
+	long int d = MAX_VALUE - (MAX_VALUE % x); /* d is divisible by x */
+	long int v = ub_random(state);
+	while(d <= v)
+		v = ub_random(state);
+	return (v % x);
+}
+
 void 
 ub_randfree(struct ub_randstate* s)
 {

util/random.h

@@ -75,6 +75,15 @@ struct ub_randstate* ub_initstate(unsigned int seed,
  */
 long int ub_random(struct ub_randstate* state);
 
+/**
+ * Generate random number between 0 and x-1.  No modulo bias.
+ * @param state: must have been initialised with ub_initstate.
+ * @param x: an upper limit. not negative or zero. must be smaller than 2**31.
+ * @return: random value between 0..x-1. Possibly more than one
+ * random number is picked from the random stream to satisfy this.
+ */
+long int ub_random_max(struct ub_randstate* state, long int x);
+
 /**
  * Delete the random state.
  * @param state: to delete.

validator/autotrust.c

@@ -1685,7 +1685,7 @@ calc_next_probe(struct module_env* env, uint32_t wait)
 		wait = 3600;
 	rnd = wait/10;
 	rest = wait-rnd;
-	rnd = (uint32_t)ub_random(env->rnd) % rnd;
+	rnd = (uint32_t)ub_random_max(env->rnd, (long int)rnd);
 	return (time_t)(*env->now + rest + rnd);
 }