From 7c770d572a719fa40fa9c82807a0bd3840baf4a0 Mon Sep 17 00:00:00 2001
From: Ben Laurie <ben@links.org>
Date: Mon, 28 Jan 2013 17:30:38 +0000
Subject: [PATCH] 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)
---
crypto/cryptlib.c | 13 +++++++++++++
crypto/crypto.h | 7 +++++++
crypto/rsa/rsa_oaep.c | 2 +-
ssl/d1_pkt.c | 2 +-
ssl/s2_clnt.c | 2 +-
ssl/s2_pkt.c | 3 +--
ssl/s3_both.c | 2 +-
ssl/s3_pkt.c | 2 +-
ssl/t1_lib.c | 2 +-
9 files changed, 27 insertions(+), 8 deletions(-)
diff --git a/crypto/cryptlib.c b/crypto/cryptlib.c
index 07b0a66217..56d82adfcd 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 d3da3c881f..3a43803a1e 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 eaae712236..c57507d214 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 987af60835..5e2c56c983 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 76b690ea13..03b6cf9673 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 ac963b2d47..8bb6ab8baa 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 349531460d..a537738f42 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 4299af1e7c..9246ff2951 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 a1a8badcda..92e8f88c53 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 */