From: Andreas Schneider <asn@samba.org>
Date: Fri, 1 Apr 2016 08:09:45 +0000 (+0200)
Subject: util: Add memcmp_const_time()
X-Git-Tag: talloc-2.1.7~224
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ba6e39076bdc5222f77c4d7615e44db0aac14e91;p=thirdparty%2Fsamba.git

util: Add memcmp_const_time()

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
---

diff --git a/lib/util/samba_util.h b/lib/util/samba_util.h
index 9d6f0d8bf26..387e957ceca 100644
--- a/lib/util/samba_util.h
+++ b/lib/util/samba_util.h
@@ -279,6 +279,19 @@ limited by 'n' bytes
 _PUBLIC_ size_t utf16_len_n(const void *src, size_t n);
 _PUBLIC_ size_t ucs2_align(const void *base_ptr, const void *p, int flags);
 
+/**
+ * @brief Constant time compare to memory regions.
+ *
+ * @param[in]  s1  The first memory region to compare.
+ *
+ * @param[in]  s2  The second memory region to compare.
+ *
+ * @param[in]  n   The length of the memory to comapre.
+ *
+ * @return 0 when the memory regions are equal, 0 if not.
+ */
+_PUBLIC_ int memcmp_const_time(const void *s1, const void *s2, size_t n);
+
 /**
 Do a case-insensitive, whitespace-ignoring string compare.
 **/
diff --git a/lib/util/util_str.c b/lib/util/util_str.c
index 673fbc7c6b5..c7d91ca3744 100644
--- a/lib/util/util_str.c
+++ b/lib/util/util_str.c
@@ -333,3 +333,15 @@ _PUBLIC_ size_t utf16_len_n(const void *src, size_t n)
 
 	return len;
 }
+
+_PUBLIC_ int memcmp_const_time(const void *s1, const void *s2, size_t n)
+{
+	const uint8_t *p1 = s1, *p2 = s2;
+	size_t i, sum = 0;
+
+	for (i = 0; i < n; i++) {
+		sum |= (p1[i] ^ p2[i]);
+	}
+
+	return sum != 0;
+}