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Set pointer to start of plaintext at record decryption time

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The SSL context structure mbedtls_ssl_context contains several pointers
ssl->in_hdr, ssl->in_len, ssl->in_iv, ssl->in_msg pointing to various
parts of the record header in an incoming record, and they are setup
in the static function ssl_update_in_pointers() based on the _expected_
transform for the next incoming record.
In particular, the pointer ssl->in_msg is set to where the record plaintext
should reside after record decryption, and an assertion double-checks this
after each call to ssl_decrypt_buf().

This commit removes the dependency of ssl_update_in_pointers() on the
expected incoming transform by setting ssl->in_msg to ssl->in_iv --
the beginning of the record content (potentially including the IV) --
and adjusting ssl->in_msg after calling ssl_decrypt_buf() on a protected
record.

Care has to be taken to not load ssl->in_msg before calling
mbedtls_ssl_read_record(), then, which was previously the
case in ssl_parse_server_hello(); the commit fixes that.
This commit is contained in:
Hanno Becker 2019-05-08 09:38:41 +01:00
parent 82e2a3961c
commit 79594fd0d4
2 changed files with 19 additions and 22 deletions
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4
library/ssl_cli.c
View File

@ -1658,8 +1658,6 @@ static int ssl_parse_server_hello( mbedtls_ssl_context *ssl )
MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse server hello" ) );
buf = ssl->in_msg;
if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
{
/* No alert on a read error. */
@ -1667,6 +1665,8 @@ static int ssl_parse_server_hello( mbedtls_ssl_context *ssl )
return( ret );
}
buf = ssl->in_msg;
if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
{
#if defined(MBEDTLS_SSL_RENEGOTIATION)

37
library/ssl_tls.c
View File

@ -110,8 +110,7 @@ static int ssl_check_timer( mbedtls_ssl_context *ssl )
static void ssl_update_out_pointers( mbedtls_ssl_context *ssl,
mbedtls_ssl_transform *transform );
static void ssl_update_in_pointers( mbedtls_ssl_context *ssl,
mbedtls_ssl_transform *transform );
static void ssl_update_in_pointers( mbedtls_ssl_context *ssl );
#define SSL_DONT_FORCE_FLUSH 0
#define SSL_FORCE_FLUSH 1
@ -5042,12 +5041,7 @@ static int ssl_prepare_record_content( mbedtls_ssl_context *ssl )
return( ret );
}
if( ssl->in_iv + rec.data_offset != ssl->in_msg )
{
/* Should never happen */
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
ssl->in_msg = rec.buf + rec.data_offset;
ssl->in_msglen = rec.data_len;
ssl->in_len[0] = (unsigned char)( rec.data_len >> 8 );
ssl->in_len[1] = (unsigned char)( rec.data_len );
@ -7037,7 +7031,7 @@ int mbedtls_ssl_parse_change_cipher_spec( mbedtls_ssl_context *ssl )
#endif /* MBEDTLS_SSL_PROTO_DTLS */
memset( ssl->in_ctr, 0, 8 );
ssl_update_in_pointers( ssl, ssl->transform_negotiate );
ssl_update_in_pointers( ssl );
#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
if( mbedtls_ssl_hw_record_activate != NULL )
@ -7991,9 +7985,18 @@ static void ssl_update_out_pointers( mbedtls_ssl_context *ssl,
* and the caller has to make sure there's space for this.
*/
static void ssl_update_in_pointers( mbedtls_ssl_context *ssl,
mbedtls_ssl_transform *transform )
static void ssl_update_in_pointers( mbedtls_ssl_context *ssl )
{
/* This function sets the pointers to match the case
* of unprotected TLS/DTLS records, with both ssl->in_iv
* and ssl->in_msg pointing to the beginning of the record
* content.
*
* When decrypting a protected record, ssl->in_msg
* will be shifted to point to the beginning of the
* record plaintext.
*/
#if defined(MBEDTLS_SSL_PROTO_DTLS)
if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
{
@ -8009,14 +8012,8 @@ static void ssl_update_in_pointers( mbedtls_ssl_context *ssl,
ssl->in_iv = ssl->in_hdr + 5;
}
/* Offset in_msg from in_iv to allow space for explicit IV, if used. */
if( transform != NULL &&
ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
{
ssl->in_msg = ssl->in_iv + transform->ivlen - transform->fixed_ivlen;
}
else
ssl->in_msg = ssl->in_iv;
/* This will be adjusted at record decryption time. */
ssl->in_msg = ssl->in_iv;
}
/*
@ -8049,7 +8046,7 @@ static void ssl_reset_in_out_pointers( mbedtls_ssl_context *ssl )
/* Derive other internal pointers. */
ssl_update_out_pointers( ssl, NULL /* no transform enabled */ );
ssl_update_in_pointers ( ssl, NULL /* no transform enabled */ );
ssl_update_in_pointers ( ssl );
}
int mbedtls_ssl_setup( mbedtls_ssl_context *ssl,