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[nginx] SSL: ssl_reject_handshake directive (ticket #195).

Maxim Dounin
October 22, 2020 11:04AM
details: https://hg.nginx.org/nginx/rev/59e1c73fe02b
branches:
changeset: 7732:59e1c73fe02b
user: Maxim Dounin <mdounin@mdounin.ru>
date: Thu Oct 22 18:02:28 2020 +0300
description:
SSL: ssl_reject_handshake directive (ticket #195).

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.

diffstat:

src/event/ngx_event_openssl.c | 12 +++-
src/event/ngx_event_openssl.h | 1 +
src/http/modules/ngx_http_ssl_module.c | 93 ++++++++++++++++++++++++---------
src/http/modules/ngx_http_ssl_module.h | 1 +
src/http/ngx_http_request.c | 41 +++++++++-----
5 files changed, 105 insertions(+), 43 deletions(-)

diffs (309 lines):

diff -r fd0b2226919b -r 59e1c73fe02b src/event/ngx_event_openssl.c
--- a/src/event/ngx_event_openssl.c Thu Oct 22 18:00:27 2020 +0300
+++ b/src/event/ngx_event_openssl.c Thu Oct 22 18:02:28 2020 +0300
@@ -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");
@@ -3354,8 +3361,9 @@ ngx_ssl_session_id_context(ngx_ssl_t *ss
}
}

- 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).
diff -r fd0b2226919b -r 59e1c73fe02b src/event/ngx_event_openssl.h
--- a/src/event/ngx_event_openssl.h Thu Oct 22 18:00:27 2020 +0300
+++ b/src/event/ngx_event_openssl.h Thu Oct 22 18:02:28 2020 +0300
@@ -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;
diff -r fd0b2226919b -r 59e1c73fe02b src/http/modules/ngx_http_ssl_module.c
--- a/src/http/modules/ngx_http_ssl_module.c Thu Oct 22 18:00:27 2020 +0300
+++ b/src/http/modules/ngx_http_ssl_module.c Thu Oct 22 18:02:28 2020 +0300
@@ -294,6 +294,13 @@ static ngx_command_t ngx_http_ssl_comma
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
};

@@ -614,6 +621,7 @@ ngx_http_ssl_create_srv_conf(ngx_conf_t
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;
@@ -660,6 +668,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *
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
@@ -707,7 +716,27 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *

if (conf->enable) {

- if (conf->certificates == NULL) {
+ 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->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;
+ }
+
+ } else if (!conf->reject_handshake) {
ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
"no \"ssl_certificate\" is defined for "
"the \"ssl\" directive in %s:%ui",
@@ -715,30 +744,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *
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;
- }
-
- } 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)
@@ -750,6 +756,9 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *
+ 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) {
@@ -808,7 +817,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *
return NGX_CONF_ERROR;
#endif

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

/* configure certificates */

@@ -947,6 +956,10 @@ ngx_http_ssl_compile_certificates(ngx_co
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;
@@ -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",
diff -r fd0b2226919b -r 59e1c73fe02b src/http/modules/ngx_http_ssl_module.h
--- a/src/http/modules/ngx_http_ssl_module.h Thu Oct 22 18:00:27 2020 +0300
+++ b/src/http/modules/ngx_http_ssl_module.h Thu Oct 22 18:02:28 2020 +0300
@@ -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;

diff -r fd0b2226919b -r 59e1c73fe02b src/http/ngx_http_request.c
--- a/src/http/ngx_http_request.c Thu Oct 22 18:00:27 2020 +0300
+++ b/src/http/ngx_http_request.c Thu Oct 22 18:02:28 2020 +0300
@@ -871,10 +871,14 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *
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,
@@ -883,7 +887,7 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *
host.len = ngx_strlen(servername);

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

host.data = (u_char *) servername;
@@ -891,32 +895,27 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *
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;
@@ -933,8 +932,7 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *

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;
}

/*
@@ -960,7 +958,22 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *
#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
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Subject Author Views Posted

[nginx] SSL: ssl_reject_handshake directive (ticket #195).

Maxim Dounin 214 October 22, 2020 11:04AM



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