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Fix renegotiation at incorrect times in DTLS

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Fix an incorrect condition in ssl_check_ctr_renegotiate() that compared
64 bits of record counter instead of 48 bits as described in RFC 6347
Section 4.3.1. This would cause the function's return value to be
occasionally incorrect and the renegotiation routines to be triggered
at unexpected times.
This commit is contained in:
Andres AG 2016-12-15 17:01:16 +00:00
parent 41ce6e6076
commit 428f28d8d7
3 changed files with 25 additions and 6 deletions
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9
ChangeLog
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@ -1,5 +1,14 @@
mbed TLS ChangeLog (Sorted per branch, date) mbed TLS ChangeLog (Sorted per branch, date)
= mbed TLS x.x.x branch released xxxx-xx-xx
Bugfix
* Fix incorrect renegotiation condition in ssl_check_ctr_renegotiate() that
would compare 64 bits of the record counter instead of 48 bits as indicated
in RFC 6347 Section 4.3.1. This could cause the execution of the
renegotiation routines at unexpected times when the protocol is DTLS. Found
by wariua. #687
= mbed TLS 2.1.6 branch released 2016-10-17 = mbed TLS 2.1.6 branch released 2016-10-17
Security Security

6
include/mbedtls/ssl.h
View file

@ -1946,7 +1946,7 @@ void mbedtls_ssl_conf_renegotiation_enforced( mbedtls_ssl_config *conf, int max_
/** /**
* \brief Set record counter threshold for periodic renegotiation. * \brief Set record counter threshold for periodic renegotiation.
* (Default: 2^64 - 256.) * (Default: 2^48 - 1)
* *
* Renegotiation is automatically triggered when a record * Renegotiation is automatically triggered when a record
* counter (outgoing or ingoing) crosses the defined * counter (outgoing or ingoing) crosses the defined
@ -1957,9 +1957,11 @@ void mbedtls_ssl_conf_renegotiation_enforced( mbedtls_ssl_config *conf, int max_
* Lower values can be used to enforce policies such as "keys * Lower values can be used to enforce policies such as "keys
* must be refreshed every N packets with cipher X". * must be refreshed every N packets with cipher X".
* *
* \note When the transport is set to MBEDTLS_SSL_TRANSPORT_DATAGRAM,
* the maximum renegotiation period is 2^48 - 1.
*
* \param conf SSL configuration * \param conf SSL configuration
* \param period The threshold value: a big-endian 64-bit number. * \param period The threshold value: a big-endian 64-bit number.
* Set to 2^64 - 1 to disable periodic renegotiation
*/ */
void mbedtls_ssl_conf_renegotiation_period( mbedtls_ssl_config *conf, void mbedtls_ssl_conf_renegotiation_period( mbedtls_ssl_config *conf,
const unsigned char period[8] ); const unsigned char period[8] );

16
library/ssl_tls.c
View file

@ -6379,6 +6379,10 @@ int mbedtls_ssl_renegotiate( mbedtls_ssl_context *ssl )
*/ */
static int ssl_check_ctr_renegotiate( mbedtls_ssl_context *ssl ) static int ssl_check_ctr_renegotiate( mbedtls_ssl_context *ssl )
{ {
size_t ep_len = ssl_ep_len( ssl );
int in_ctr_cmp;
int out_ctr_cmp;
if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER || if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER ||
ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING || ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING ||
ssl->conf->disable_renegotiation == MBEDTLS_SSL_RENEGOTIATION_DISABLED ) ssl->conf->disable_renegotiation == MBEDTLS_SSL_RENEGOTIATION_DISABLED )
@ -6386,8 +6390,12 @@ static int ssl_check_ctr_renegotiate( mbedtls_ssl_context *ssl )
return( 0 ); return( 0 );
} }
if( memcmp( ssl->in_ctr, ssl->conf->renego_period, 8 ) <= 0 && in_ctr_cmp = memcmp( ssl->in_ctr + ep_len,
memcmp( ssl->out_ctr, ssl->conf->renego_period, 8 ) <= 0 ) ssl->conf->renego_period + ep_len, 8 - ep_len );
out_ctr_cmp = memcmp( ssl->out_ctr + ep_len,
ssl->conf->renego_period + ep_len, 8 - ep_len );
if( in_ctr_cmp <= 0 && out_ctr_cmp <= 0 )
{ {
return( 0 ); return( 0 );
} }
@ -7119,8 +7127,8 @@ int mbedtls_ssl_config_defaults( mbedtls_ssl_config *conf,
#if defined(MBEDTLS_SSL_RENEGOTIATION) #if defined(MBEDTLS_SSL_RENEGOTIATION)
conf->renego_max_records = MBEDTLS_SSL_RENEGO_MAX_RECORDS_DEFAULT; conf->renego_max_records = MBEDTLS_SSL_RENEGO_MAX_RECORDS_DEFAULT;
memset( conf->renego_period, 0xFF, 7 ); memset( conf->renego_period, 0x00, 2 );
conf->renego_period[7] = 0x00; memset( conf->renego_period + 2, 0xFF, 6 );
#endif #endif
#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C) #if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)