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Merge pull request #944 from AndrzejKurek/clihlo_cookie_pxy_fix_2_28

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[Backport 2.28] Add a client hello cookie_len overflow test
This commit is contained in:
Gilles Peskine
2022-06-20 19:35:54 +02:00
committed by GitHub
parent 7e163d796c 719c723afc
commit bb54fce91e
6 changed files with 133 additions and 30 deletions
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9
ChangeLog.d/cookie_parsing_bug.txt Normal file
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@@ -0,0 +1,9 @@
Security
* Fix a buffer overread in DTLS ClientHello parsing in servers with
MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE enabled. An unauthenticated client
or a man-in-the-middle could cause a DTLS server to read up to 255 bytes
after the end of the SSL input buffer. The buffer overread only happens
when MBEDTLS_SSL_IN_CONTENT_LEN is less than a threshold that depends on
the exact configuration: 258 bytes if using mbedtls_ssl_cookie_check(),
and possibly up to 571 bytes with a custom cookie check function.
Reported by the Cybeats PSI Team.

8
include/mbedtls/ssl_internal.h
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@@ -1306,4 +1306,12 @@ void mbedtls_ssl_buffering_free( mbedtls_ssl_context *ssl );
void mbedtls_ssl_flight_free( mbedtls_ssl_flight_item *flight );
#endif /* MBEDTLS_SSL_PROTO_DTLS */
#if defined(MBEDTLS_TEST_HOOKS)
int mbedtls_ssl_check_dtls_clihlo_cookie(
mbedtls_ssl_context *ssl,
const unsigned char *cli_id, size_t cli_id_len,
const unsigned char *in, size_t in_len,
unsigned char *obuf, size_t buf_len, size_t *olen );
#endif
#endif /* ssl_internal.h */

79
library/ssl_msg.c
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@@ -3229,8 +3229,8 @@ void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl )
#if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
/*
* Without any SSL context, check if a datagram looks like a ClientHello with
* a valid cookie, and if it doesn't, generate a HelloVerifyRequest message.
* Check if a datagram looks like a ClientHello with a valid cookie,
* and if it doesn't, generate a HelloVerifyRequest message.
* Both input and output include full DTLS headers.
*
* - if cookie is valid, return 0
@@ -3239,10 +3239,9 @@ void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl )
* return MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED
* - otherwise return a specific error code
*/
static int ssl_check_dtls_clihlo_cookie(
mbedtls_ssl_cookie_write_t *f_cookie_write,
mbedtls_ssl_cookie_check_t *f_cookie_check,
void *p_cookie,
MBEDTLS_STATIC_TESTABLE
int mbedtls_ssl_check_dtls_clihlo_cookie(
mbedtls_ssl_context *ssl,
const unsigned char *cli_id, size_t cli_id_len,
const unsigned char *in, size_t in_len,
unsigned char *obuf, size_t buf_len, size_t *olen )
@@ -3276,26 +3275,53 @@ static int ssl_check_dtls_clihlo_cookie(
*
* Minimum length is 61 bytes.
*/
if( in_len < 61 ||
in[0] != MBEDTLS_SSL_MSG_HANDSHAKE ||
MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: in_len=%u",
(unsigned) in_len ) );
MBEDTLS_SSL_DEBUG_BUF( 4, "cli_id", cli_id, cli_id_len );
if( in_len < 61 )
{
MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: record too short" ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
}
if( in[0] != MBEDTLS_SSL_MSG_HANDSHAKE ||
in[3] != 0 || in[4] != 0 ||
in[19] != 0 || in[20] != 0 || in[21] != 0 )
{
MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: not a good ClientHello" ) );
MBEDTLS_SSL_DEBUG_MSG( 4, ( " type=%u epoch=%u fragment_offset=%u",
in[0],
(unsigned) in[3] << 8 | in[4],
(unsigned) in[19] << 16 | in[20] << 8 | in[21] ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
}
sid_len = in[59];
if( sid_len > in_len - 61 )
if( 59 + 1 + sid_len + 1 > in_len )
{
MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: sid_len=%u > %u",
(unsigned) sid_len,
(unsigned) in_len - 61 ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
}
MBEDTLS_SSL_DEBUG_BUF( 4, "sid received from network",
in + 60, sid_len );
cookie_len = in[60 + sid_len];
if( cookie_len > in_len - 60 )
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
if( f_cookie_check( p_cookie, in + sid_len + 61, cookie_len,
cli_id, cli_id_len ) == 0 )
if( 59 + 1 + sid_len + 1 + cookie_len > in_len )
{
/* Valid cookie */
MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: cookie_len=%u > %u",
(unsigned) cookie_len,
(unsigned) ( in_len - sid_len - 61 ) ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
}
MBEDTLS_SSL_DEBUG_BUF( 4, "cookie received from network",
in + sid_len + 61, cookie_len );
if( ssl->conf->f_cookie_check( ssl->conf->p_cookie,
in + sid_len + 61, cookie_len,
cli_id, cli_id_len ) == 0 )
{
MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: valid" ) );
return( 0 );
}
@@ -3330,8 +3356,9 @@ static int ssl_check_dtls_clihlo_cookie(
/* Generate and write actual cookie */
p = obuf + 28;
if( f_cookie_write( p_cookie,
&p, obuf + buf_len, cli_id, cli_id_len ) != 0 )
if( ssl->conf->f_cookie_write( ssl->conf->p_cookie,
&p, obuf + buf_len,
cli_id, cli_id_len ) != 0 )
{
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
@@ -3385,15 +3412,13 @@ static int ssl_handle_possible_reconnect( mbedtls_ssl_context *ssl )
return( 0 );
}
ret = ssl_check_dtls_clihlo_cookie(
ssl->conf->f_cookie_write,
ssl->conf->f_cookie_check,
ssl->conf->p_cookie,
ret = mbedtls_ssl_check_dtls_clihlo_cookie(
ssl,
ssl->cli_id, ssl->cli_id_len,
ssl->in_buf, ssl->in_left,
ssl->out_buf, MBEDTLS_SSL_OUT_CONTENT_LEN, &len );
MBEDTLS_SSL_DEBUG_RET( 2, "ssl_check_dtls_clihlo_cookie", ret );
MBEDTLS_SSL_DEBUG_RET( 2, "mbedtls_ssl_check_dtls_clihlo_cookie", ret );
if( ret == MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED )
{
@@ -3571,7 +3596,6 @@ static int ssl_parse_record_header( mbedtls_ssl_context const *ssl,
/*
* Parse and validate record version
*/
rec->ver[0] = buf[ rec_hdr_version_offset + 0 ];
rec->ver[1] = buf[ rec_hdr_version_offset + 1 ];
mbedtls_ssl_read_version( &major_ver, &minor_ver,
@@ -3580,16 +3604,19 @@ static int ssl_parse_record_header( mbedtls_ssl_context const *ssl,
if( major_ver != ssl->major_ver )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "major version mismatch" ) );
MBEDTLS_SSL_DEBUG_MSG( 1, ( "major version mismatch: got %u, expected %u",
(unsigned) major_ver,
(unsigned) ssl->major_ver ) );
return( MBEDTLS_ERR_SSL_INVALID_RECORD );
}
if( minor_ver > ssl->conf->max_minor_ver )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "minor version mismatch" ) );
MBEDTLS_SSL_DEBUG_MSG( 1, ( "minor version mismatch: got %u, expected max %u",
(unsigned) minor_ver,
(unsigned) ssl->conf->max_minor_ver ) );
return( MBEDTLS_ERR_SSL_INVALID_RECORD );
}
/*
* Parse/Copy record sequence number.
*/

21
library/ssl_srv.c
View File

@@ -1604,11 +1604,19 @@ read_record_header:
MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, handshake len.: %d",
( buf[1] << 16 ) | ( buf[2] << 8 ) | buf[3] ) );
/* We don't support fragmentation of ClientHello (yet?) */
if( buf[1] != 0 ||
msg_len != mbedtls_ssl_hs_hdr_len( ssl ) + ( ( buf[2] << 8 ) | buf[3] ) )
if( buf[1] != 0 )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message: %u != 0",
(unsigned) buf[1] ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
}
/* We don't support fragmentation of ClientHello (yet?) */
if( msg_len != mbedtls_ssl_hs_hdr_len( ssl ) + ( ( buf[2] << 8 ) | buf[3] ) )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message: %u != %u + %u",
(unsigned) msg_len,
(unsigned) mbedtls_ssl_hs_hdr_len( ssl ),
(unsigned) ( buf[2] << 8 ) | buf[3] ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
}
@@ -1649,6 +1657,11 @@ read_record_header:
* For now we don't support fragmentation, so make sure
* fragment_offset == 0 and fragment_length == length
*/
MBEDTLS_SSL_DEBUG_MSG(
4, ( "fragment_offset=%u fragment_length=%u length=%u",
(unsigned) ( ssl->in_msg[6] << 16 | ssl->in_msg[7] << 8 | ssl->in_msg[8] ),
(unsigned) ( ssl->in_msg[9] << 16 | ssl->in_msg[10] << 8 | ssl->in_msg[11] ),
(unsigned) ( ssl->in_msg[1] << 16 | ssl->in_msg[2] << 8 | ssl->in_msg[3] ) ) );
if( ssl->in_msg[6] != 0 || ssl->in_msg[7] != 0 || ssl->in_msg[8] != 0 ||
memcmp( ssl->in_msg + 1, ssl->in_msg + 9, 3 ) != 0 )
{

18
tests/suites/test_suite_ssl.data
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@@ -10689,3 +10689,21 @@ raw_key_agreement_fail:0
Raw key agreement: bad server key
raw_key_agreement_fail:1
Cookie parsing: nominal run
cookie_parsing:"16fefd0000000000000000002F010000de000000000000011efefd7b7272727272727272727272727272727272727272727272727272727272727d00200000000000000000000000000000000000000000000000000000000000000000":MBEDTLS_ERR_SSL_INTERNAL_ERROR
Cookie parsing: cookie_len overflow
cookie_parsing:"16fefd000000000000000000ea010000de000000000000011efefd7b7272727272727272727272727272727272727272727272727272727272727db97b7373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737373737db963":MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO
Cookie parsing: non-zero fragment offset
cookie_parsing:"16fefd00000000000000000032010000de000072000000011efefd7b7272727272727272727272727272727272727272727272727272727272727d01730143":MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO
Cookie parsing: sid_len overflow
cookie_parsing:"16fefd00000000000000000032010000de000000000000011efefd7b7272727272727272727272727272727272727272727272727272727272727dFF730143":MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO
Cookie parsing: record too short
cookie_parsing:"16fefd0000000000000000002f010000de000000000000011efefd7b7272727272727272727272727272727272727272727272727272727272727dFF":MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO
Cookie parsing: one byte overread
cookie_parsing:"16fefd0000000000000000002F010000de000000000000011efefd7b7272727272727272727272727272727272727272727272727272727272727d0001":MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO

28
tests/suites/test_suite_ssl.function
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@@ -4624,3 +4624,31 @@ exit:
USE_PSA_DONE( );
}
/* END_CASE */
/* BEGIN_CASE depends_on:MBEDTLS_SSL_SRV_C:MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE:MBEDTLS_TEST_HOOKS */
void cookie_parsing( data_t *cookie, int exp_ret )
{
mbedtls_ssl_context ssl;
mbedtls_ssl_config conf;
size_t len;
mbedtls_ssl_init( &ssl );
mbedtls_ssl_config_init( &conf );
TEST_EQUAL( mbedtls_ssl_config_defaults( &conf, MBEDTLS_SSL_IS_SERVER,
MBEDTLS_SSL_TRANSPORT_DATAGRAM,
MBEDTLS_SSL_PRESET_DEFAULT ),
0 );
TEST_EQUAL( mbedtls_ssl_setup( &ssl, &conf ), 0 );
TEST_EQUAL( mbedtls_ssl_check_dtls_clihlo_cookie( &ssl, ssl.cli_id,
ssl.cli_id_len,
cookie->x, cookie->len,
ssl.out_buf,
MBEDTLS_SSL_OUT_CONTENT_LEN,
&len ),
exp_ret );
mbedtls_ssl_free( &ssl );
mbedtls_ssl_config_free( &conf );
}
/* END_CASE */