Mailing List Archive

Author: icing
Date: Fri Jun 11 10:45:25 2021
New Revision: 1890693

URL: http://svn.apache.org/viewvc?rev=1890693&view=rev
Log:
*) mod_ssl: tighten the handling of ALPN for outgoing (proxy)
connections. If ALPN protocols are provided and sent to the
remote server, the received protocol selected is inspected
and checked for a match. Without match, the peer handshake
fails.
An exception is the proposal of "http/1.1" where it is
accepted if the remote server did not answer ALPN with
a selected protocol. This accomodates for hosts that do
not observe/support ALPN and speak http/1.x be default.


Added:
httpd/httpd/trunk/changes-entries/ssl_alpn_outgoing.txt
Modified:
httpd/httpd/trunk/modules/ssl/ssl_engine_io.c

Added: httpd/httpd/trunk/changes-entries/ssl_alpn_outgoing.txt
URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/changes-entries/ssl_alpn_outgoing.txt?rev=1890693&view=auto
==============================================================================
--- httpd/httpd/trunk/changes-entries/ssl_alpn_outgoing.txt (added)
+++ httpd/httpd/trunk/changes-entries/ssl_alpn_outgoing.txt Fri Jun 11 10:45:25 2021
@@ -0,0 +1,9 @@
+ *) mod_ssl: tighten the handling of ALPN for outgoing (proxy)
+ connections. If ALPN protocols are provided and sent to the
+ remote server, the received protocol selected is inspected
+ and checked for a match. Without match, the peer handshake
+ fails.
+ An exception is the proposal of "http/1.1" where it is
+ accepted if the remote server did not answer ALPN with
+ a selected protocol. This accomodates for hosts that do
+ not observe/support ALPN and speak http/1.x be default.
\ No newline at end of file

Modified: httpd/httpd/trunk/modules/ssl/ssl_engine_io.c
URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/modules/ssl/ssl_engine_io.c?rev=1890693&r1=1890692&r2=1890693&view=diff
==============================================================================
--- httpd/httpd/trunk/modules/ssl/ssl_engine_io.c (original)
+++ httpd/httpd/trunk/modules/ssl/ssl_engine_io.c Fri Jun 11 10:45:25 2021
@@ -1253,6 +1253,8 @@ static apr_status_t ssl_io_filter_handsh
"proxy-request-hostname");
#ifdef HAVE_TLS_ALPN
const char *alpn_note;
+ apr_array_header_t *alpn_proposed = NULL;
+ int alpn_empty_ok = 1;
#endif
BOOL proxy_ssl_check_peer_ok = TRUE;
int post_handshake_rc = OK;
@@ -1265,9 +1267,16 @@ static apr_status_t ssl_io_filter_handsh
#ifdef HAVE_TLS_ALPN
alpn_note = apr_table_get(c->notes, "proxy-request-alpn-protos");
if (alpn_note) {
- char *protos, *s, *p, *last;
+ char *protos, *s, *p, *last, *proto;
apr_size_t len;

+ /* Transform the note into a protocol formatted byte array:
+ * (len-byte proto-char+)*
+ * We need the remote server to agree on one of these, unless 'http/1.1'
+ * is also among our proposals. Because pre-ALPN remotes will speak this.
+ */
+ alpn_proposed = apr_array_make(c->pool, 3, sizeof(const char*));
+ alpn_empty_ok = 0;
s = protos = apr_pcalloc(c->pool, strlen(alpn_note)+1);
p = apr_pstrdup(c->pool, alpn_note);
while ((p = apr_strtok(p, ", ", &last))) {
@@ -1279,6 +1288,11 @@ static apr_status_t ssl_io_filter_handsh
ssl_log_ssl_error(SSLLOG_MARK, APLOG_ERR, server);
return APR_EGENERAL;
}
+ proto = apr_pstrndup(c->pool, p, len);
+ APR_ARRAY_PUSH(alpn_proposed, const char*) = proto;
+ if (!strcmp("http/1.1", proto)) {
+ alpn_empty_ok = 1;
+ }
*s++ = (unsigned char)len;
while (len--) {
*s++ = *p++;
@@ -1294,6 +1308,8 @@ static apr_status_t ssl_io_filter_handsh
ap_log_cerror(APLOG_MARK, APLOG_WARNING, 0, c, APLOGNO(03310)
"error setting alpn protos from '%s'", alpn_note);
ssl_log_ssl_error(SSLLOG_MARK, APLOG_WARNING, server);
+ /* If ALPN was requested and we cannot do it, we must fail */
+ return MODSSL_ERROR_BAD_GATEWAY;
}
}
#endif /* defined HAVE_TLS_ALPN */
@@ -1385,6 +1401,50 @@ static apr_status_t ssl_io_filter_handsh
}
}

+#ifdef HAVE_TLS_ALPN
+ /* If we proposed ALPN protocol(s), we need to check if the server
+ * agreed to one of them. While <https://www.rfc-editor.org/rfc/rfc7301.txt>
+ * chapter 3.2 says the server SHALL error the handshake in such a case,
+ * the reality is that some servers fall back to their default, e.g. http/1.1.
+ * (we also do this right now)
+ * We need to treat this as an error for security reasons.
+ */
+ if (alpn_proposed && alpn_proposed->nelts > 0) {
+ const char *selected;
+ unsigned int slen;
+
+ SSL_get0_alpn_selected(filter_ctx->pssl, (const unsigned char**)&selected, &slen);
+ if (!selected || !slen) {
+ /* No ALPN selection reported by the remote server. This could mean
+ * it does not support ALPN (old server) or that it does not support
+ * any of our proposals (Apache itself up to 2.4.48 at least did that). */
+ if (!alpn_empty_ok) {
+ ap_log_cerror(APLOG_MARK, APLOG_INFO, 0, c, APLOGNO()
+ "SSL Proxy: Peer did not select any of our ALPN protocols [%s].",
+ alpn_note);
+ proxy_ssl_check_peer_ok = FALSE;
+ }
+ }
+ else {
+ const char *proto;
+ int i, found = 0;
+ for (i = 0; !found && i < alpn_proposed->nelts; ++i) {
+ proto = APR_ARRAY_IDX(alpn_proposed, i, const char *);
+ found = !strncmp(selected, proto, slen);
+ }
+ if (!found) {
+ /* From a conforming peer, this should never happen,
+ * but life always finds a way... */
+ proto = apr_pstrndup(c->pool, selected, slen);
+ ap_log_cerror(APLOG_MARK, APLOG_INFO, 0, c, APLOGNO()
+ "SSL Proxy: Peer proposed ALPN protocol %s which is none "
+ "of our proposals [%s].", proto, alpn_note);
+ proxy_ssl_check_peer_ok = FALSE;
+ }
+ }
+ }
+#endif
+
if (proxy_ssl_check_peer_ok == TRUE) {
/* another chance to fail */
post_handshake_rc = ssl_run_proxy_post_handshake(c, filter_ctx->pssl);