From: Ben Laurie <ben@links.org>
Date: Mon, 28 Jan 2013 17:30:38 +0000 (+0000)
Subject: Add and use a constant-time memcmp.
X-Git-Tag: master-pre-reformat~1407
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7c770d572a719fa40fa9c82807a0bd3840baf4a0;p=thirdparty%2Fopenssl.git

Add and use a constant-time memcmp.

This change adds CRYPTO_memcmp, which compares two vectors of bytes in
an amount of time that's independent of their contents. It also changes
several MAC compares in the code to use this over the standard memcmp,
which may leak information about the size of a matching prefix.
(cherry picked from commit 2ee798880a246d648ecddadc5b91367bee4a5d98)
---

diff --git a/crypto/cryptlib.c b/crypto/cryptlib.c
index 07b0a662176..56d82adfcd2 100644
--- a/crypto/cryptlib.c
+++ b/crypto/cryptlib.c
@@ -397,3 +397,16 @@ void OpenSSLDie(const char *file,int line,const char *assertion)
 #ifndef OPENSSL_FIPSCANISTER
 void *OPENSSL_stderr(void)	{ return stderr; }
 #endif
+
+int CRYPTO_memcmp(const void *in_a, const void *in_b, size_t len)
+	{
+	size_t i;
+	const unsigned char *a = in_a;
+	const unsigned char *b = in_b;
+	unsigned char x = 0;
+
+	for (i = 0; i < len; i++)
+		x |= a[i] ^ b[i];
+
+	return x;
+	}
diff --git a/crypto/crypto.h b/crypto/crypto.h
index d3da3c881f5..3a43803a1ed 100644
--- a/crypto/crypto.h
+++ b/crypto/crypto.h
@@ -567,6 +567,13 @@ int FIPS_mode_set(int r);
 
 void OPENSSL_init(void);
 
+/* CRYPTO_memcmp returns zero iff the |len| bytes at |a| and |b| are equal. It
+ * takes an amount of time dependent on |len|, but independent of the contents
+ * of |a| and |b|. Unlike memcmp, it cannot be used to put elements into a
+ * defined order as the return value when a != b is undefined, other than to be
+ * non-zero. */
+int CRYPTO_memcmp(const void *a, const void *b, size_t len);
+
 /* BEGIN ERROR CODES */
 /* The following lines are auto generated by the script mkerr.pl. Any changes
  * made after this point may be overwritten when the script is next run.
diff --git a/crypto/rsa/rsa_oaep.c b/crypto/rsa/rsa_oaep.c
index eaae7122368..c57507d2144 100644
--- a/crypto/rsa/rsa_oaep.c
+++ b/crypto/rsa/rsa_oaep.c
@@ -151,7 +151,7 @@ int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 	if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
 		return -1;
 
-	if (memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad)
+	if (CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad)
 		goto decoding_err;
 	else
 		{
diff --git a/ssl/d1_pkt.c b/ssl/d1_pkt.c
index 987af608358..5e2c56c9833 100644
--- a/ssl/d1_pkt.c
+++ b/ssl/d1_pkt.c
@@ -463,7 +463,7 @@ printf("\n");
 		else
 			rr->length = 0;
 		i=s->method->ssl3_enc->mac(s,md,0);
-		if (i < 0 || mac == NULL || memcmp(md, mac, mac_size) != 0)
+		if (i < 0 || mac == NULL || CRYPTO_memcmp(md,mac,mac_size) != 0)
 			{
 			decryption_failed_or_bad_record_mac = 1;
 			}
diff --git a/ssl/s2_clnt.c b/ssl/s2_clnt.c
index 76b690ea134..03b6cf96738 100644
--- a/ssl/s2_clnt.c
+++ b/ssl/s2_clnt.c
@@ -939,7 +939,7 @@ static int get_server_verify(SSL *s)
 		s->msg_callback(0, s->version, 0, p, len, s, s->msg_callback_arg); /* SERVER-VERIFY */
 	p += 1;
 
-	if (memcmp(p,s->s2->challenge,s->s2->challenge_length) != 0)
+	if (CRYPTO_memcmp(p,s->s2->challenge,s->s2->challenge_length) != 0)
 		{
 		ssl2_return_error(s,SSL2_PE_UNDEFINED_ERROR);
 		SSLerr(SSL_F_GET_SERVER_VERIFY,SSL_R_CHALLENGE_IS_DIFFERENT);
diff --git a/ssl/s2_pkt.c b/ssl/s2_pkt.c
index ac963b2d47d..8bb6ab8baa3 100644
--- a/ssl/s2_pkt.c
+++ b/ssl/s2_pkt.c
@@ -269,8 +269,7 @@ static int ssl2_read_internal(SSL *s, void *buf, int len, int peek)
 			s->s2->ract_data_length-=mac_size;
 			ssl2_mac(s,mac,0);
 			s->s2->ract_data_length-=s->s2->padding;
-			if (	(memcmp(mac,s->s2->mac_data,
-				(unsigned int)mac_size) != 0) ||
+			if (	(CRYPTO_memcmp(mac,s->s2->mac_data,mac_size) != 0) ||
 				(s->s2->rlength%EVP_CIPHER_CTX_block_size(s->enc_read_ctx) != 0))
 				{
 				SSLerr(SSL_F_SSL2_READ_INTERNAL,SSL_R_BAD_MAC_DECODE);
diff --git a/ssl/s3_both.c b/ssl/s3_both.c
index 349531460d3..a537738f429 100644
--- a/ssl/s3_both.c
+++ b/ssl/s3_both.c
@@ -265,7 +265,7 @@ int ssl3_get_finished(SSL *s, int a, int b)
 		goto f_err;
 		}
 
-	if (memcmp(p, s->s3->tmp.peer_finish_md, i) != 0)
+	if (CRYPTO_memcmp(p, s->s3->tmp.peer_finish_md, i) != 0)
 		{
 		al=SSL_AD_DECRYPT_ERROR;
 		SSLerr(SSL_F_SSL3_GET_FINISHED,SSL_R_DIGEST_CHECK_FAILED);
diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c
index 4299af1e7cc..9246ff2951e 100644
--- a/ssl/s3_pkt.c
+++ b/ssl/s3_pkt.c
@@ -465,7 +465,7 @@ printf("\n");
 #endif
 			}
 		i=s->method->ssl3_enc->mac(s,md,0);
-		if (i < 0 || mac == NULL || memcmp(md, mac, (size_t)mac_size) != 0)
+		if (i < 0 || mac == NULL || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0)
 			{
 			decryption_failed_or_bad_record_mac = 1;
 			}
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index a1a8badcda0..92e8f88c53f 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -3125,7 +3125,7 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick, int eticklen,
 	HMAC_Update(&hctx, etick, eticklen);
 	HMAC_Final(&hctx, tick_hmac, NULL);
 	HMAC_CTX_cleanup(&hctx);
-	if (memcmp(tick_hmac, etick + eticklen, mlen))
+	if (CRYPTO_memcmp(tick_hmac, etick + eticklen, mlen))
 		return 2;
 	/* Attempt to decrypt session data */
 	/* Move p after IV to start of encrypted ticket, update length */