4 files changed, 79 insertions, 6 deletions

diff --git a/contrib/ntp/lib/isc/hmacmd5.c b/contrib/ntp/lib/isc/hmacmd5.c
index 6abe6e27df8e..0388b17083b7 100644
--- a/contrib/ntp/lib/isc/hmacmd5.c
+++ b/contrib/ntp/lib/isc/hmacmd5.c
@@ -145,5 +145,5 @@ isc_hmacmd5_verify2(isc_hmacmd5_t *ctx, unsigned char *digest, size_t len) {
 
 	REQUIRE(len <= ISC_MD5_DIGESTLENGTH);
 	isc_hmacmd5_sign(ctx, newdigest);
-	return (ISC_TF(memcmp(digest, newdigest, len) == 0));
+	return (ISC_TF(isc_tsmemcmp(digest, newdigest, len) == 0));
 }
diff --git a/contrib/ntp/lib/isc/hmacsha.c b/contrib/ntp/lib/isc/hmacsha.c
index d7b9f1897eb0..75b1cb14d29d 100644
--- a/contrib/ntp/lib/isc/hmacsha.c
+++ b/contrib/ntp/lib/isc/hmacsha.c
@@ -538,7 +538,7 @@ isc_hmacsha1_verify(isc_hmacsha1_t *ctx, unsigned char *digest, size_t len) {
 
 	REQUIRE(len <= ISC_SHA1_DIGESTLENGTH);
 	isc_hmacsha1_sign(ctx, newdigest, ISC_SHA1_DIGESTLENGTH);
-	return (ISC_TF(memcmp(digest, newdigest, len) == 0));
+	return (ISC_TF(isc_tsmemcmp(digest, newdigest, len) == 0));
 }
 
 /*
@@ -551,7 +551,7 @@ isc_hmacsha224_verify(isc_hmacsha224_t *ctx, unsigned char *digest, size_t len)
 
 	REQUIRE(len <= ISC_SHA224_DIGESTLENGTH);
 	isc_hmacsha224_sign(ctx, newdigest, ISC_SHA224_DIGESTLENGTH);
-	return (ISC_TF(memcmp(digest, newdigest, len) == 0));
+	return (ISC_TF(isc_tsmemcmp(digest, newdigest, len) == 0));
 }
 
 /*
@@ -564,7 +564,7 @@ isc_hmacsha256_verify(isc_hmacsha256_t *ctx, unsigned char *digest, size_t len)
 
 	REQUIRE(len <= ISC_SHA256_DIGESTLENGTH);
 	isc_hmacsha256_sign(ctx, newdigest, ISC_SHA256_DIGESTLENGTH);
-	return (ISC_TF(memcmp(digest, newdigest, len) == 0));
+	return (ISC_TF(isc_tsmemcmp(digest, newdigest, len) == 0));
 }
 
 /*
@@ -577,7 +577,7 @@ isc_hmacsha384_verify(isc_hmacsha384_t *ctx, unsigned char *digest, size_t len)
 
 	REQUIRE(len <= ISC_SHA384_DIGESTLENGTH);
 	isc_hmacsha384_sign(ctx, newdigest, ISC_SHA384_DIGESTLENGTH);
-	return (ISC_TF(memcmp(digest, newdigest, len) == 0));
+	return (ISC_TF(isc_tsmemcmp(digest, newdigest, len) == 0));
 }
 
 /*
@@ -590,5 +590,5 @@ isc_hmacsha512_verify(isc_hmacsha512_t *ctx, unsigned char *digest, size_t len)
 
 	REQUIRE(len <= ISC_SHA512_DIGESTLENGTH);
 	isc_hmacsha512_sign(ctx, newdigest, ISC_SHA512_DIGESTLENGTH);
-	return (ISC_TF(memcmp(digest, newdigest, len) == 0));
+	return (ISC_TF(isc_tsmemcmp(digest, newdigest, len) == 0));
 }
diff --git a/contrib/ntp/lib/isc/include/isc/string.h b/contrib/ntp/lib/isc/include/isc/string.h
index b49fdbc327f1..395b550218fc 100644
--- a/contrib/ntp/lib/isc/include/isc/string.h
+++ b/contrib/ntp/lib/isc/include/isc/string.h
@@ -199,6 +199,24 @@ isc_string_regiondup(isc_mem_t *mctx, const isc_region_t *source);
  *
  */
 
+int
+isc_tsmemcmp(const void *p1, const void *p2, size_t len);
+/*
+ * Lexicographic compare 'len' unsigned bytes from 'p1' and 'p2'
+ * like 'memcmp()'.
+ *
+ * This function is safe from timing attacks as it has a runtime that
+ * only depends on 'len' and has no early-out option.
+ *
+ * Use this to check MACs and other material that is security sensitive.
+ *
+ * Returns:
+ *  (let x be the byte offset of the first different byte)
+ *  -1 if (u_char)p1[x] < (u_char)p2[x]
+ *   1 if (u_char)p1[x] > (u_char)p2[x]
+ *   0 if byte series are equal
+ */
+
 char *
 isc_string_separate(char **stringp, const char *delim);
 
diff --git a/contrib/ntp/lib/isc/tsmemcmp.c b/contrib/ntp/lib/isc/tsmemcmp.c
new file mode 100644
index 000000000000..e6af42eafc0f
--- /dev/null
+++ b/contrib/ntp/lib/isc/tsmemcmp.c
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2004-2007, 2011, 2012  Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (C) 1999-2001, 2003  Internet Software Consortium.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+ * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* $Id$ */
+
+/*! \file */
+
+#include <config.h>
+#include <limits.h>
+#include <isc/string.h>
+
+/* Making a portable memcmp that has no internal branches and loops always
+ * once for every byte without early-out shortcut has a few challenges.
+ *
+ * Inspired by 'timingsafe_memcmp()' from the BSD system and
+ * https://github.com/libressl-portable/openbsd/blob/master/src/lib/libc/string/timingsafe_memcmp.c
+ *
+ * Sadly, that one is not portable C: It makes assumptions on the representation
+ * of negative integers and assumes sign-preserving right-shift of negative
+ * signed values. This is a rewrite from scratch that should not suffer from
+ * such issues.
+ *
+ * 2015-12-12, J. Perlinger (perlinger-at-ntp-dot-org)
+ */
+int
+isc_tsmemcmp(const void *p1, const void *p2, size_t nb) {
+	const unsigned char *ucp1 = p1;
+	const unsigned char *ucp2 = p2;
+	unsigned int isLT = 0u;
+	unsigned int isGT = 0u;
+	volatile unsigned int mask = (1u << CHAR_BIT);
+
+	for (/*NOP*/; 0 != nb; --nb, ++ucp1, ++ucp2) {
+		isLT |= mask &
+		    ((unsigned int)*ucp1 - (unsigned int)*ucp2);
+		isGT |= mask &
+		    ((unsigned int)*ucp2 - (unsigned int)*ucp1);
+		mask &= ~(isLT | isGT);
+	}
+	return (int)(isGT >> CHAR_BIT) - (int)(isLT >> CHAR_BIT);
+}