diff options
author | Ben Laurie <ben@links.org> | 2013-01-28 17:34:33 +0000 |
---|---|---|
committer | Dr. Stephen Henson <steve@openssl.org> | 2013-02-06 13:56:13 +0000 |
commit | 1326a64a3301310e0a8d45d9e5651f651c9f30b2 (patch) | |
tree | 40ff03bad6a17b1dc19ca88ded609a1c15d7545e /ssl/d1_pkt.c | |
parent | e0da2c2ed29a3a66c22e6a8a5072b58399835d71 (diff) |
Update DTLS code to match CBC decoding in TLS.
This change updates the DTLS code to match the constant-time CBC
behaviour in the TLS.
(cherry picked from commit 9f27de170d1b7bef3d46d41382dc4dafde8b3900)
Diffstat (limited to 'ssl/d1_pkt.c')
-rw-r--r-- | ssl/d1_pkt.c | 86 |
1 files changed, 50 insertions, 36 deletions
diff --git a/ssl/d1_pkt.c b/ssl/d1_pkt.c index 4763d5cd1f..02c881ab31 100644 --- a/ssl/d1_pkt.c +++ b/ssl/d1_pkt.c @@ -376,15 +376,11 @@ static int dtls1_process_record(SSL *s) { int i,al; - int clear=0; int enc_err; SSL_SESSION *sess; SSL3_RECORD *rr; unsigned int mac_size; unsigned char md[EVP_MAX_MD_SIZE]; - int decryption_failed_or_bad_record_mac = 0; - unsigned char *mac = NULL; - rr= &(s->s3->rrec); sess = s->session; @@ -417,12 +413,16 @@ dtls1_process_record(SSL *s) rr->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) { - /* To minimize information leaked via timing, we will always - * perform all computations before discarding the message. - */ - decryption_failed_or_bad_record_mac = 1; + /* For DTLS we simply ignore bad packets. */ + rr->length = 0; + s->packet_length = 0; + goto err; } #ifdef TLS_DEBUG @@ -432,45 +432,59 @@ printf("\n"); #endif /* r->length is now the compressed data plus mac */ - if ( (sess == NULL) || - (s->enc_read_ctx == NULL) || - (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 */ - int t; - t=EVP_MD_CTX_size(s->read_hash); - OPENSSL_assert(t >= 0); - mac_size=t; - - if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+mac_size) + /* 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 <= EVP_MAX_MD_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 (rr->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 && + rr->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_DTLS1_PROCESS_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 >= 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); rr->length -= mac_size; - mac = &rr->data[rr->length]; } else - rr->length = 0; - i=s->method->ssl3_enc->mac(s,md,0); - if (i < 0 || mac == NULL || CRYPTO_memcmp(md,mac,mac_size) != 0) { - decryption_failed_or_bad_record_mac = 1; + /* In this case there's no padding, so |rec->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 /* not send */); + if (i < 0 || mac == NULL || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0) + enc_err = -1; + if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+mac_size) + enc_err = -1; } - if (decryption_failed_or_bad_record_mac) + if (enc_err < 0) { /* decryption failed, silently discard message */ rr->length = 0; |