ssl/*: remove SSL3_RECORD->orig_len to restore binary compatibility.

[openssl.git] / ssl / s3_pkt.c

diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c
index 9246ff2951e2db9185aa0680325dbe12b65971e5..64cef2abfae205e50d1bc55c280e20862d46ed7f 100644 (file)
--- a/ssl/s3_pkt.c
+++ b/ssl/s3_pkt.c
@@ -290,11 +290,8 @@ static int ssl3_get_record(SSL *s)
        unsigned char *p;
        unsigned char md[EVP_MAX_MD_SIZE];
        short version;
-       int mac_size;
-       int clear=0;
+       unsigned mac_size, orig_len;
        size_t extra;
-       int decryption_failed_or_bad_record_mac = 0;
-       unsigned char *mac = NULL;
 
        rr= &(s->s3->rrec);
        sess=s->session;
@@ -403,19 +400,18 @@ fprintf(stderr, "Record type=%d, Length=%d\n", rr->type, rr->length);
 
        /* decrypt in place in 'rr->input' */
        rr->data=rr->input;
+       orig_len=rr->length;
 
        enc_err = s->method->ssl3_enc->enc(s,0);
-       if (enc_err <= 0)
+       /* enc_err is:
+        *    0: (in non-constant time) if the record is publically invalid.
+        *    1: if the padding is valid
+        *    -1: if the padding is invalid */
+       if (enc_err == 0)
                {
-               if (enc_err == 0)
-                       /* SSLerr() and ssl3_send_alert() have been called */
-                       goto err;
-
-               /* Otherwise enc_err == -1, which indicates bad padding
-                * (rec->length has not been changed in this case).
-                * To minimize information leaked via timing, we will perform
-                * the MAC computation anyway. */
-               decryption_failed_or_bad_record_mac = 1;
+               al=SSL_AD_DECRYPTION_FAILED;
+               SSLerr(SSL_F_TLS1_ENC,SSL_R_BLOCK_CIPHER_PAD_IS_WRONG);
+               goto f_err;
                }
 
 #ifdef TLS_DEBUG
@@ -425,53 +421,59 @@ printf("\n");
 #endif
 
        /* r->length is now the compressed data plus mac */
-       if (    (sess == NULL) ||
-               (s->enc_read_ctx == NULL) ||
-               (EVP_MD_CTX_md(s->read_hash) == NULL))
-               clear=1;
-
-       if (!clear)
+       if ((sess != NULL) &&
+           (s->enc_read_ctx != NULL) &&
+           (EVP_MD_CTX_md(s->read_hash) != NULL))
                {
-               /* !clear => s->read_hash != NULL => mac_size != -1 */
+               /* s->read_hash != NULL => mac_size != -1 */
+               unsigned char *mac = NULL;
+               unsigned char mac_tmp[EVP_MAX_MD_SIZE];
                mac_size=EVP_MD_CTX_size(s->read_hash);
-               OPENSSL_assert(mac_size >= 0);
+               OPENSSL_assert(mac_size <= EVP_MAX_MD_SIZE);
 
-               if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
+               /* orig_len is the length of the record before any padding was
+                * removed. This is public information, as is the MAC in use,
+                * therefore we can safely process the record in a different
+                * amount of time if it's too short to possibly contain a MAC.
+                */
+               if (orig_len < mac_size ||
+                   /* CBC records must have a padding length byte too. */
+                   (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
+                    orig_len < mac_size+1))
                        {
-#if 0 /* OK only for stream ciphers (then rr->length is visible from ciphertext anyway) */
-                       al=SSL_AD_RECORD_OVERFLOW;
-                       SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_PRE_MAC_LENGTH_TOO_LONG);
+                       al=SSL_AD_DECODE_ERROR;
+                       SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
                        goto f_err;
-#else
-                       decryption_failed_or_bad_record_mac = 1;
-#endif                 
                        }
-               /* check the MAC for rr->input (it's in mac_size bytes at the tail) */
-               if (rr->length >= (unsigned int)mac_size)
+
+               if (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE)
                        {
+                       /* We update the length so that the TLS header bytes
+                        * can be constructed correctly but we need to extract
+                        * the MAC in constant time from within the record,
+                        * without leaking the contents of the padding bytes.
+                        * */
+                       mac = mac_tmp;
+                       ssl3_cbc_copy_mac(mac_tmp, rr, mac_size, orig_len);
                        rr->length -= mac_size;
-                       mac = &rr->data[rr->length];
                        }
                else
                        {
-                       /* record (minus padding) is too short to contain a MAC */
-#if 0 /* OK only for stream ciphers */
-                       al=SSL_AD_DECODE_ERROR;
-                       SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
-                       goto f_err;
-#else
-                       decryption_failed_or_bad_record_mac = 1;
-                       rr->length = 0;
-#endif
+                       /* In this case there's no padding, so |orig_len|
+                        * equals |rec->length| and we checked that there's
+                        * enough bytes for |mac_size| above. */
+                       rr->length -= mac_size;
+                       mac = &rr->data[rr->length];
                        }
-               i=s->method->ssl3_enc->mac(s,md,0);
+
+               i=s->method->ssl3_enc->mac(s,md,0 /* not send */);
                if (i < 0 || mac == NULL || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0)
-                       {
-                       decryption_failed_or_bad_record_mac = 1;
-                       }
+                       enc_err = -1;
+               if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
+                       enc_err = -1;
                }
 
-       if (decryption_failed_or_bad_record_mac)
+       if (enc_err < 0)
                {
                /* A separate 'decryption_failed' alert was introduced with TLS 1.0,
                 * SSL 3.0 only has 'bad_record_mac'.  But unless a decryption