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Disable dtls fragmentation for ClientHello messages

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Set the handshake mtu to unlimited when encountering a ClienHello message and
reset it to its previous value after writing the record.
This commit is contained in:
Andrzej Kurek 2018-10-03 09:16:44 -04:00
parent db9ad837c9
commit 7fa9903bd0
1 changed files with 19 additions and 0 deletions
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19
library/ssl_tls.c
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@ -212,7 +212,10 @@ static int ssl_double_retransmit_timeout( mbedtls_ssl_context *ssl )
* delivered) of any compliant IPv4 (and IPv6) network, and should work * delivered) of any compliant IPv4 (and IPv6) network, and should work
* on most non-IP stacks too. */ * on most non-IP stacks too. */
if( ssl->handshake->retransmit_timeout != ssl->conf->hs_timeout_min ) if( ssl->handshake->retransmit_timeout != ssl->conf->hs_timeout_min )
{
ssl->handshake->mtu = 508; ssl->handshake->mtu = 508;
MBEDTLS_SSL_DEBUG_MSG( 2, ( "mtu autoreduction to %d bytes", ssl->handshake->mtu ) );
}
new_timeout = 2 * ssl->handshake->retransmit_timeout; new_timeout = 2 * ssl->handshake->retransmit_timeout;
@ -2945,6 +2948,7 @@ int mbedtls_ssl_resend( mbedtls_ssl_context *ssl )
int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl ) int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
{ {
int ret; int ret;
uint16_t mtu_temp = 0;
MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> mbedtls_ssl_flight_transmit" ) ); MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> mbedtls_ssl_flight_transmit" ) );
if( ssl->handshake->retransmit_state != MBEDTLS_SSL_RETRANS_SENDING ) if( ssl->handshake->retransmit_state != MBEDTLS_SSL_RETRANS_SENDING )
@ -2979,6 +2983,15 @@ int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
ssl_swap_epochs( ssl ); ssl_swap_epochs( ssl );
} }
/* Disable handshake mtu for client hello message to avoid fragmentation.
* Setting it back after calling mbedtls_ssl_write_record */
if( ssl->out_msg[0] == MBEDTLS_SSL_HS_CLIENT_HELLO )
{
mtu_temp = ssl->handshake->mtu;
ssl->handshake->mtu = 0;
MBEDTLS_SSL_DEBUG_MSG( 2, ( "disabling fragmentation of ClientHello message" ) );
}
ret = ssl_get_remaining_payload_in_datagram( ssl ); ret = ssl_get_remaining_payload_in_datagram( ssl );
if( ret < 0 ) if( ret < 0 )
return( ret ); return( ret );
@ -3077,6 +3090,12 @@ int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret ); MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
return( ret ); return( ret );
} }
if( mtu_temp != 0 )
{
ssl->handshake->mtu = mtu_temp;
mtu_temp = 0;
}
} }
if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 ) if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )