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 07b0a66217645feedeeab008c95b5b8c428db0c1..56d82adfcd2c2884389f70b200ac14343c458faf 100644 (file)
--- 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 d3da3c881f57240247dcedb991dbc775f2b4ed3a..3a43803a1ed34fffa3362d52c7e4ecdfa6c590fd 100644 (file)
--- 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 eaae71223682099f737e5c8377894662de1a15da..c57507d214480eff5872d3ec5ce5ceb5cbb2c25a 100644 (file)
--- 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 987af608358d914a72fa8a4620d7faf8188d22f0..5e2c56c9833ddcb85c0286de0e2cb89c9cbf9578 100644 (file)
--- 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 76b690ea1340f04bad5c9eeb25e3cc9dc43ed9cb..03b6cf9673809a7582c4c176c30a75b7e0e1b6a4 100644 (file)
--- 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 ac963b2d47d6e369adc012ffac5c8df4ddc7f4bb..8bb6ab8baa33501dcd6f0991d53ad80b3d9361aa 100644 (file)
--- 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 349531460d39f54da0e9474d913ac70370df9d7f..a537738f4298971a61304ab130921f81ab6b652a 100644 (file)
--- 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 4299af1e7cccf343d6ec8eb26f041514588306e1..9246ff2951e2db9185aa0680325dbe12b65971e5 100644 (file)
--- 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 a1a8badcda0b2d86b6dfdfc280a262ddd53764dc..92e8f88c53f09a71fb2496144fe0b98a2043537f 100644 (file)
--- 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 */