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Fix bounds check in ssl_parse_server_psk_hint()

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In the previous bounds check `(*p) > end - len`, the computation
of `end - len` might underflow if `end` is within the first 64KB
of the address space (note that the length `len` is controlled by
the peer). In this case, the bounds check will be bypassed, leading
to `*p` exceed the message bounds by up to 64KB when leaving
`ssl_parse_server_psk_hint()`. In a pure PSK-based handshake,
this doesn't seem to have any consequences, as `*p*` is not accessed
afterwards. In a PSK-(EC)DHE handshake, however, `*p` is read from
in `ssl_parse_server_ecdh_params()` and `ssl_parse_server_dh_params()`
which might lead to an application crash of information leakage.
This commit is contained in:
Hanno Becker 2018-10-08 13:40:50 +01:00
parent 0592ea772a
commit 0c161d1956
1 changed files with 2 additions and 2 deletions
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4
library/ssl_cli.c
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@ -2097,7 +2097,7 @@ static int ssl_parse_server_psk_hint( mbedtls_ssl_context *ssl,
* *
* opaque psk_identity_hint<0..2^16-1>; * opaque psk_identity_hint<0..2^16-1>;
*/ */
if( (*p) > end - 2 ) if( end - (*p) < 2 )
{ {
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message " MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message "
"(psk_identity_hint length)" ) ); "(psk_identity_hint length)" ) );
@ -2106,7 +2106,7 @@ static int ssl_parse_server_psk_hint( mbedtls_ssl_context *ssl,
len = (*p)[0] << 8 | (*p)[1]; len = (*p)[0] << 8 | (*p)[1];
*p += 2; *p += 2;
if( (*p) > end - len ) if( end - (*p) < len )
{ {
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message " MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message "
"(psk_identity_hint length)" ) ); "(psk_identity_hint length)" ) );