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SSL: ssl_reject_handshake directive (ticket #195).
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In some cases it might be needed to reject SSL handshake based on SNI
server name provided, for example, to make sure an invalid certificate
is not returned to clients trying to contact a name-based virtual server
without SSL configured.  Previously, a "ssl_ciphers aNULL;" was used for
this.  This workaround, however, is not compatible with TLSv1.3, in
particular, when using BoringSSL, where it is not possible to configure
TLSv1.3 ciphers at all.

With this change, the ssl_reject_handshake directive is introduced,
which instructs nginx to reject SSL handshakes with an "unrecognized_name"
alert in a particular server block.

For example, to reject handshake with names other than example.com,
one can use the following configuration:

    server {
        listen 443 ssl;
        ssl_reject_handshake on;
    }

    server {
        listen 443 ssl;
        server_name example.com;
        ssl_certificate example.com.crt;
        ssl_certificate_key example.com.key;
    }

The following configuration can be used to reject all SSL handshakes
without SNI server name provided:

    server {
        listen 443 ssl;
        ssl_reject_handshake on;
    }

    server {
        listen 443 ssl;
        server_name ~^;
        ssl_certificate example.crt;
        ssl_certificate_key example.key;
    }

Additionally, the ssl_reject_handshake directive makes configuring
certificates for the default server block optional.  If no certificates
are configured in the default server for a given listening socket,
certificates must be defined in all non-default server blocks with
the listening socket in question.
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mdounin committed Oct 22, 2020
1 parent f9a3724 commit 9cdb278
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Showing 5 changed files with 104 additions and 42 deletions.
12 changes: 10 additions & 2 deletions src/event/ngx_event_openssl.c
Original file line number Diff line number Diff line change
Expand Up @@ -1793,6 +1793,13 @@ ngx_ssl_handshake(ngx_connection_t *c)
return NGX_ERROR;
}

if (c->ssl->handshake_rejected) {
ngx_connection_error(c, err, "handshake rejected");
ERR_clear_error();

return NGX_ERROR;
}

c->read->error = 1;

ngx_ssl_connection_error(c, sslerr, err, "SSL_do_handshake() failed");
Expand Down Expand Up @@ -3354,8 +3361,9 @@ ngx_ssl_session_id_context(ngx_ssl_t *ssl, ngx_str_t *sess_ctx,
}
}

if (SSL_CTX_get_ex_data(ssl->ctx, ngx_ssl_certificate_index) == NULL) {

if (SSL_CTX_get_ex_data(ssl->ctx, ngx_ssl_certificate_index) == NULL
&& certificates != NULL)
{
/*
* If certificates are loaded dynamically, we use certificate
* names as specified in the configuration (with variables).
Expand Down
1 change: 1 addition & 0 deletions src/event/ngx_event_openssl.h
Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,7 @@ struct ngx_ssl_connection_s {
u_char early_buf;

unsigned handshaked:1;
unsigned handshake_rejected:1;
unsigned renegotiation:1;
unsigned buffer:1;
unsigned no_wait_shutdown:1;
Expand Down
91 changes: 65 additions & 26 deletions src/http/modules/ngx_http_ssl_module.c
Original file line number Diff line number Diff line change
Expand Up @@ -294,6 +294,13 @@ static ngx_command_t ngx_http_ssl_commands[] = {
offsetof(ngx_http_ssl_srv_conf_t, conf_commands),
&ngx_http_ssl_conf_command_post },

{ ngx_string("ssl_reject_handshake"),
NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_CONF_FLAG,
ngx_conf_set_flag_slot,
NGX_HTTP_SRV_CONF_OFFSET,
offsetof(ngx_http_ssl_srv_conf_t, reject_handshake),
NULL },

ngx_null_command
};

Expand Down Expand Up @@ -614,6 +621,7 @@ ngx_http_ssl_create_srv_conf(ngx_conf_t *cf)
sscf->enable = NGX_CONF_UNSET;
sscf->prefer_server_ciphers = NGX_CONF_UNSET;
sscf->early_data = NGX_CONF_UNSET;
sscf->reject_handshake = NGX_CONF_UNSET;
sscf->buffer_size = NGX_CONF_UNSET_SIZE;
sscf->verify = NGX_CONF_UNSET_UINT;
sscf->verify_depth = NGX_CONF_UNSET_UINT;
Expand Down Expand Up @@ -660,6 +668,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
prev->prefer_server_ciphers, 0);

ngx_conf_merge_value(conf->early_data, prev->early_data, 0);
ngx_conf_merge_value(conf->reject_handshake, prev->reject_handshake, 0);

ngx_conf_merge_bitmask_value(conf->protocols, prev->protocols,
(NGX_CONF_BITMASK_SET|NGX_SSL_TLSv1
Expand Down Expand Up @@ -707,38 +716,35 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)

if (conf->enable) {

if (conf->certificates == NULL) {
ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate\" is defined for "
"the \"ssl\" directive in %s:%ui",
conf->file, conf->line);
return NGX_CONF_ERROR;
}
if (conf->certificates) {
if (conf->certificate_keys == NULL) {
ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate_key\" is defined for "
"the \"ssl\" directive in %s:%ui",
conf->file, conf->line);
return NGX_CONF_ERROR;
}

if (conf->certificate_keys == NULL) {
ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate_key\" is defined for "
"the \"ssl\" directive in %s:%ui",
conf->file, conf->line);
return NGX_CONF_ERROR;
}
if (conf->certificate_keys->nelts < conf->certificates->nelts) {
ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate_key\" is defined "
"for certificate \"%V\" and "
"the \"ssl\" directive in %s:%ui",
((ngx_str_t *) conf->certificates->elts)
+ conf->certificates->nelts - 1,
conf->file, conf->line);
return NGX_CONF_ERROR;
}

if (conf->certificate_keys->nelts < conf->certificates->nelts) {
} else if (!conf->reject_handshake) {
ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate_key\" is defined "
"for certificate \"%V\" and "
"no \"ssl_certificate\" is defined for "
"the \"ssl\" directive in %s:%ui",
((ngx_str_t *) conf->certificates->elts)
+ conf->certificates->nelts - 1,
conf->file, conf->line);
return NGX_CONF_ERROR;
}

} else {

if (conf->certificates == NULL) {
return NGX_CONF_OK;
}
} else if (conf->certificates) {

if (conf->certificate_keys == NULL
|| conf->certificate_keys->nelts < conf->certificates->nelts)
Expand All @@ -750,6 +756,9 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
+ conf->certificates->nelts - 1);
return NGX_CONF_ERROR;
}

} else if (!conf->reject_handshake) {
return NGX_CONF_OK;
}

if (ngx_ssl_create(&conf->ssl, conf->protocols, conf) != NGX_OK) {
Expand Down Expand Up @@ -808,7 +817,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
return NGX_CONF_ERROR;
#endif

} else {
} else if (conf->certificates) {

/* configure certificates */

Expand Down Expand Up @@ -947,6 +956,10 @@ ngx_http_ssl_compile_certificates(ngx_conf_t *cf,
ngx_http_complex_value_t *cv;
ngx_http_compile_complex_value_t ccv;

if (conf->certificates == NULL) {
return NGX_OK;
}

cert = conf->certificates->elts;
key = conf->certificate_keys->elts;
nelts = conf->certificates->nelts;
Expand Down Expand Up @@ -1327,7 +1340,33 @@ ngx_http_ssl_init(ngx_conf_t *cf)
cscf = addr[a].default_server;
sscf = cscf->ctx->srv_conf[ngx_http_ssl_module.ctx_index];

if (sscf->certificates == NULL) {
if (sscf->certificates) {
continue;
}

if (!sscf->reject_handshake) {
ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate\" is defined for "
"the \"listen ... ssl\" directive in %s:%ui",
cscf->file_name, cscf->line);
return NGX_ERROR;
}

/*
* if no certificates are defined in the default server,
* check all non-default server blocks
*/

cscfp = addr[a].servers.elts;
for (s = 0; s < addr[a].servers.nelts; s++) {

cscf = cscfp[s];
sscf = cscf->ctx->srv_conf[ngx_http_ssl_module.ctx_index];

if (sscf->certificates || sscf->reject_handshake) {
continue;
}

ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate\" is defined for "
"the \"listen ... ssl\" directive in %s:%ui",
Expand Down
1 change: 1 addition & 0 deletions src/http/modules/ngx_http_ssl_module.h
Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ typedef struct {

ngx_flag_t prefer_server_ciphers;
ngx_flag_t early_data;
ngx_flag_t reject_handshake;

ngx_uint_t protocols;

Expand Down
41 changes: 27 additions & 14 deletions src/http/ngx_http_request.c
Original file line number Diff line number Diff line change
Expand Up @@ -871,10 +871,14 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
return SSL_TLSEXT_ERR_ALERT_FATAL;
}

hc = c->data;

servername = SSL_get_servername(ssl_conn, TLSEXT_NAMETYPE_host_name);

if (servername == NULL) {
return SSL_TLSEXT_ERR_OK;
ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
"SSL server name: null");
goto done;
}

ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
Expand All @@ -883,40 +887,35 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
host.len = ngx_strlen(servername);

if (host.len == 0) {
return SSL_TLSEXT_ERR_OK;
goto done;
}

host.data = (u_char *) servername;

rc = ngx_http_validate_host(&host, c->pool, 1);

if (rc == NGX_ERROR) {
*ad = SSL_AD_INTERNAL_ERROR;
return SSL_TLSEXT_ERR_ALERT_FATAL;
goto error;
}

if (rc == NGX_DECLINED) {
return SSL_TLSEXT_ERR_OK;
goto done;
}

hc = c->data;

rc = ngx_http_find_virtual_server(c, hc->addr_conf->virtual_names, &host,
NULL, &cscf);

if (rc == NGX_ERROR) {
*ad = SSL_AD_INTERNAL_ERROR;
return SSL_TLSEXT_ERR_ALERT_FATAL;
goto error;
}

if (rc == NGX_DECLINED) {
return SSL_TLSEXT_ERR_OK;
goto done;
}

hc->ssl_servername = ngx_palloc(c->pool, sizeof(ngx_str_t));
if (hc->ssl_servername == NULL) {
*ad = SSL_AD_INTERNAL_ERROR;
return SSL_TLSEXT_ERR_ALERT_FATAL;
goto error;
}

*hc->ssl_servername = host;
Expand All @@ -933,8 +932,7 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)

if (sscf->ssl.ctx) {
if (SSL_set_SSL_CTX(ssl_conn, sscf->ssl.ctx) == NULL) {
*ad = SSL_AD_INTERNAL_ERROR;
return SSL_TLSEXT_ERR_ALERT_FATAL;
goto error;
}

/*
Expand All @@ -960,7 +958,22 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
#endif
}

done:

sscf = ngx_http_get_module_srv_conf(hc->conf_ctx, ngx_http_ssl_module);

if (sscf->reject_handshake) {
c->ssl->handshake_rejected = 1;
*ad = SSL_AD_UNRECOGNIZED_NAME;
return SSL_TLSEXT_ERR_ALERT_FATAL;
}

return SSL_TLSEXT_ERR_OK;

error:

*ad = SSL_AD_INTERNAL_ERROR;
return SSL_TLSEXT_ERR_ALERT_FATAL;
}

#endif
Expand Down

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