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mod_ssl: negotiate the TLS protocol version per name based vhost configuration.

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By using the new ClientHello callback provided by OpenSSL 1.1.1, which runs at
the earliest connection stage, we can switch the SSL_CTX of the SSL connection
early enough for OpenSSL to take into account the protocol configuration of the
vhost.

In other words:
    SSL_set_SSL_CTX(c->SSL, s->SSL_CTX)
followed by:
    SSL_set_{min,max}_proto_version(SSL_CTX_get_{min,max}_proto_version(s->SSL_CTX))
works as expected at this stage (while the same from the SNI callback is
ignored by/due to OpenSSL's state machine).

Extracting the SNI (to select the relevant vhost) in the ClientHello callback
is not as easy as calling SSL_get_servername() though, we have to work with
the raw TLS extensions helpers provided by OpenSSL. I stole this code from a
test in the OpenSSL source code (i.e. client_hello_select_server_ctx() in
test/handshake_helper.c).

We can then call init_vhost() as with the SNI callback (in use only for OpenSSL
versions earlier than 1.1.1 now), and pass it the extracted SNI.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1868645 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Yann Ylavic
2019-10-20 10:50:33 +00:00
parent 82b7e77b82
commit 076e28399c
3 changed files with 91 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

78
modules/ssl/ssl_engine_kernel.c
View File

@@ -2346,9 +2346,8 @@ static apr_status_t set_challenge_creds(conn_rec *c, const char *servername,
* This function sets the virtual host from an extended
* client hello with a server name indication extension ("SNI", cf. RFC 6066).
*/
static apr_status_t init_vhost(conn_rec *c, SSL *ssl)
static apr_status_t init_vhost(conn_rec *c, SSL *ssl, const char *servername)
{
const char *servername;
X509 *cert;
EVP_PKEY *key;
@@ -2360,7 +2359,9 @@ static apr_status_t init_vhost(conn_rec *c, SSL *ssl)
return APR_SUCCESS;
}
servername = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
if (!servername) {
servername = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
}
if (servername) {
if (ap_vhost_iterate_given_conn(c, ssl_find_vhost,
(void *)servername)) {
@@ -2410,6 +2411,7 @@ static apr_status_t init_vhost(conn_rec *c, SSL *ssl)
return APR_NOTFOUND;
}
#if OPENSSL_VERSION_NUMBER < 0x10101000L || defined(LIBRESSL_VERSION_NUMBER)
/*
* This callback function is executed when OpenSSL encounters an extended
* client hello with a server name indication extension ("SNI", cf. RFC 6066).
@@ -2417,10 +2419,69 @@ static apr_status_t init_vhost(conn_rec *c, SSL *ssl)
int ssl_callback_ServerNameIndication(SSL *ssl, int *al, modssl_ctx_t *mctx)
{
conn_rec *c = (conn_rec *)SSL_get_app_data(ssl);
apr_status_t status = init_vhost(c, ssl);
apr_status_t status = init_vhost(c, ssl, NULL);
return (status == APR_SUCCESS)? SSL_TLSEXT_ERR_OK : SSL_TLSEXT_ERR_NOACK;
}
#else /* OPENSSL_VERSION_NUMBER < 0x10101000L */
/*
* This callback function when the ClientHello is received.
*/
int ssl_callback_ClientHello(SSL *ssl, int *al, void *arg)
{
char *servername = NULL;
conn_rec *c = (conn_rec *)SSL_get_app_data(ssl);
const unsigned char *pos;
size_t len, remaining;
(void)arg;
/* We can't use SSL_get_servername() at this earliest OpenSSL connection
* stage, and there is no SSL_client_hello_get0_servername() provided as
* of OpenSSL 1.1.1. So the code below, that extracts the SNI from the
* ClientHello's TLS extensions, is taken from some test code in OpenSSL,
* i.e. client_hello_select_server_ctx() in "test/handshake_helper.c".
*/
/*
* The server_name extension was given too much extensibility when it
* was written, so parsing the normal case is a bit complex.
*/
if (!SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_server_name, &pos,
&remaining)
|| remaining <= 2)
goto give_up;
/* Extract the length of the supplied list of names. */
len = (*(pos++) << 8);
len += *(pos++);
if (len + 2 != remaining)
goto give_up;
remaining = len;
/*
* The list in practice only has a single element, so we only consider
* the first one.
*/
if (remaining <= 3 || *pos++ != TLSEXT_NAMETYPE_host_name)
goto give_up;
remaining--;
/* Now we can finally pull out the byte array with the actual hostname. */
len = (*(pos++) << 8);
len += *(pos++);
if (len + 2 != remaining)
goto give_up;
/* Use the SNI to switch to the relevant vhost, should it differ from
* c->base_server.
*/
servername = apr_pstrmemdup(c->pool, (const char *)pos, len);
give_up:
init_vhost(c, ssl, servername);
return SSL_CLIENT_HELLO_SUCCESS;
}
#endif /* OPENSSL_VERSION_NUMBER < 0x10101000L */
/*
* Find a (name-based) SSL virtual host where either the ServerName
@@ -2441,12 +2502,19 @@ static int ssl_find_vhost(void *servername, conn_rec *c, server_rec *s)
if (found && (ssl = sslcon->ssl) &&
(sc = mySrvConfig(s))) {
SSL_CTX *ctx = SSL_set_SSL_CTX(ssl, sc->server->ssl_ctx);
/*
* SSL_set_SSL_CTX() only deals with the server cert,
* so we need to duplicate a few additional settings
* from the ctx by hand
*/
SSL_set_options(ssl, SSL_CTX_get_options(ctx));
#if OPENSSL_VERSION_NUMBER >= 0x10100000L \
&& (!defined(LIBRESSL_VERSION_NUMBER) \
|| LIBRESSL_VERSION_NUMBER >= 0x20800000L)
SSL_set_min_proto_version(ssl, SSL_CTX_get_min_proto_version(ctx));
SSL_set_max_proto_version(ssl, SSL_CTX_get_max_proto_version(ctx));
#endif
if ((SSL_get_verify_mode(ssl) == SSL_VERIFY_NONE) ||
(SSL_num_renegotiations(ssl) == 0)) {
/*
@@ -2643,7 +2711,7 @@ int ssl_callback_alpn_select(SSL *ssl,
* they callback the SNI. We need to make sure that we know which vhost
* we are dealing with so we respect the correct protocols.
*/
init_vhost(c, ssl);
init_vhost(c, ssl, NULL);
proposed = ap_select_protocol(c, NULL, sslconn->server, client_protos);
if (!proposed) {