From: Petr Špaček <petr.spacek@nic.cz>
Date: Mon, 10 Dec 2018 17:43:00 +0000 (+0100)
Subject: kr_random_coin: do not crash on invalid values
X-Git-Tag: v3.2.0~13^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2fb36d26a25df9518b4e4de5c2cfcf363ce6b9a6;p=thirdparty%2Fknot-resolver.git

kr_random_coin: do not crash on invalid values
---

diff --git a/lib/utils.h b/lib/utils.h
index fb59236b6..0ec283b0c 100644
--- a/lib/utils.h
+++ b/lib/utils.h
@@ -189,7 +189,7 @@ KR_EXPORT
 void kr_rnd_buffered(void *data, unsigned int size);
 
 /** Return a few random bytes. */
-static inline uint64_t kr_rand_bytes(int size)
+static inline uint64_t kr_rand_bytes(unsigned int size)
 {
 	uint64_t result;
 	if (size <= 0 || size > sizeof(result)) {
@@ -204,25 +204,27 @@ static inline uint64_t kr_rand_bytes(int size)
 	 * (Tested via reading assembly from usual gcc -O2 setup.)
 	 * Alternatively we could waste more rnd bytes, but that seemed worse. */
 	result = 0;
-	for (int i = 0; i < size; ++ i) {
+	for (unsigned int i = 0; i < size; ++ i) {
 		result |= ((size_t)data[i]) << (i * 8);
 	}
 	return result;
 }
 
 /** Throw a pseudo-random coin, succeeding approximately with probability nomin/denomin.
- * - low precision, only one byte of randomness
- * - the most extreme bias is 1:255
+ * - low precision, only one byte of randomness (or none with extreme parameters)
  * - tip: use !kr_rand_coin() to get the complementary probability
  */
-static inline bool kr_rand_coin(int nomin, int denomin)
+static inline bool kr_rand_coin(unsigned int nomin, unsigned int denomin)
 {
-	if (nomin < 0 || denomin <= 0 || nomin > denomin) {
-		kr_log_error("kr_rand_coin(): EINVAL\n");
-		abort();
-	}
+	/* This function might be called with non-constant values
+	 * so we try to handle odd corner cases instead of crash. */
+	if (nomin >= denomin)
+		return true;
+	else if (nomin <= 0)
+		return false;
+
 	/* threshold = how many parts from 256 are a success */
-	int threshold = (nomin * 256 + /*rounding*/ denomin / 2) / denomin;
+	unsigned int threshold = (nomin * 256 + /*rounding*/ denomin / 2) / denomin;
 	if (threshold == 0) threshold = 1;
 	if (threshold == 256) threshold = 255;
 	return (kr_rand_bytes(1) < threshold);