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Add function to check is HS msg is a proper fragment

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This commit introduces a static function ssl_hs_is_proper_fragment()
to check if the current incoming handshake message is a proper fragment.
It is used within mbedtls_ssl_prepare_handshake_record() to decide whether
handshake reassembly through ssl_reassemble_dtls_handshake() is needed.

The commit changes the behavior of the library in the (unnatural)
situation where proper fragments for a handshake message are followed
by a non-fragmented version of the same message. In this case,
the previous code invoked the handshake reassembly routine
ssl_reassemble_dtls_handshake(), while with this commit, the full
handshake message is directly forwarded to the user, no altering
the handshake reassembly state -- in particular, not freeing it.
As a remedy, freeing of a potential handshake reassembly structure
is now done as part of the handshake update function
mbedtls_ssl_update_handshake_status().
This commit is contained in:
Hanno Becker 2018-08-16 09:30:53 +01:00
parent d07df86871
commit e25e3b7d96
1 changed files with 20 additions and 9 deletions
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29
library/ssl_tls.c
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@ -3409,6 +3409,17 @@ int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, uint8_t force_flush )
}
#if defined(MBEDTLS_SSL_PROTO_DTLS)
static int ssl_hs_is_proper_fragment( mbedtls_ssl_context *ssl )
{
if( ssl->in_msglen < ssl->in_hslen ||
memcmp( ssl->in_msg + 6, "\0\0\0", 3 ) != 0 ||
memcmp( ssl->in_msg + 9, ssl->in_msg + 1, 3 ) != 0 )
{
return( 1 );
}
return( 0 );
}
/*
* Mark bits in bitmask (used for DTLS HS reassembly)
*/
@ -3636,9 +3647,6 @@ static int ssl_reassemble_dtls_handshake( mbedtls_ssl_context *ssl )
memcpy( ssl->in_msg, ssl->handshake->hs_msg, ssl->in_hslen );
mbedtls_free( ssl->handshake->hs_msg );
ssl->handshake->hs_msg = NULL;
MBEDTLS_SSL_DEBUG_BUF( 3, "reassembled handshake message",
ssl->in_msg, ssl->in_hslen );
@ -3646,6 +3654,7 @@ static int ssl_reassemble_dtls_handshake( mbedtls_ssl_context *ssl )
}
#endif /* MBEDTLS_SSL_PROTO_DTLS */
int mbedtls_ssl_prepare_handshake_record( mbedtls_ssl_context *ssl )
{
if( ssl->in_msglen < mbedtls_ssl_hs_hdr_len( ssl ) )
@ -3713,12 +3722,7 @@ int mbedtls_ssl_prepare_handshake_record( mbedtls_ssl_context *ssl )
}
/* Wait until message completion to increment in_msg_seq */
/* Reassemble if current message is fragmented or reassembly is
* already in progress */
if( ssl->in_msglen < ssl->in_hslen ||
memcmp( ssl->in_msg + 6, "\0\0\0", 3 ) != 0 ||
memcmp( ssl->in_msg + 9, ssl->in_msg + 1, 3 ) != 0 ||
( ssl->handshake != NULL && ssl->handshake->hs_msg != NULL ) )
if( ssl_hs_is_proper_fragment( ssl ) == 1 )
{
MBEDTLS_SSL_DEBUG_MSG( 2, ( "found fragmented DTLS handshake message" ) );
@ -3756,6 +3760,13 @@ void mbedtls_ssl_update_handshake_status( mbedtls_ssl_context *ssl )
ssl->handshake != NULL )
{
ssl->handshake->in_msg_seq++;
/* Clear up handshake reassembly structure, if any. */
if( ssl->handshake->hs_msg != NULL )
{
mbedtls_free( ssl->handshake->hs_msg );
ssl->handshake->hs_msg = NULL;
}
}
#endif
}