libreboot-utils: improved randomness test

and the module bias handling is fully correct

Signed-off-by: Leah Rowe <leah@libreboot.org>

1 files changed, 36 insertions, 12 deletions

diff --git a/util/libreboot-utils/lib/rand.c b/util/libreboot-utils/lib/rand.c
index 63cb3fcd..c0dc8064 100644
--- a/util/libreboot-utils/lib/rand.c
+++ b/util/libreboot-utils/lib/rand.c
@@ -79,42 +79,66 @@
 #endif
 
 int
-win_lottery(char **buf) /* are u lucky? */
+win_lottery(void) /* are u lucky? */
 {
-	size_t size = 0;
-	int rval;
+	size_t size = rsize();
+	size_t size2 = rsize();
+	int rval = 0;
 
-	char *s1 = rmalloc(&size);
-	char *s2 = rmalloc(&size);
+	char *s1 = NULL; 
+	char *s2 = NULL;
 
-	if (scmp(s1, s2, BUFSIZ + 1, &rval) >= 0 &&
-	    rval == 0)
+	if (size != size2)
+		goto out;
+
+	s1 = mkrbuf(size);
+	s2 = mkrbuf(size);
+
+	if (!memcmp(s1, s2, size))
 		rval = 1; /* winner! */
 	else
 		rval = 0;
 
-	(void) scat(s1, s2, BUFSIZ << 1, buf);
-
+out:
 	free_if_null(&s1);
 	free_if_null(&s2);
 
 	return rval;
 }
 
+size_t
+rsize(void)
+{
+	size_t rval = 0;
+	size_t size = 67108864;
+
+	/* clamp rand to prevent modulo bias */
+	size_t limit = SIZE_MAX - (SIZE_MAX % size);
+
+	do {
+		rset(&rval, sizeof(rval));
+	} while (rval >= limit);
+
+	return rval % size;
+}
+
+
 void *
 rmalloc(size_t *rval)
 {
+	size_t size = 16777216;
+
 	/* clamp rand to prevent modulo bias */
-	size_t limit = SIZE_MAX - (SIZE_MAX % BUFSIZ);
+	size_t limit = SIZE_MAX - (SIZE_MAX % size);
 
 	if (if_err(rval == NULL, EFAULT))
 		return NULL;
 
 	do {
 		rset(rval, sizeof(*rval));
-	} while (*rval >= limit);
+	} while (*rval >= limit || *rval == 0);
 
-	return mkrstr(*rval %= BUFSIZ);
+	return mkrstr(*rval %= size);
 }
 
 char *