bpo-32185: Don't send IP in SNI TLS extension (#5865)

The SSL module no longer sends IP addresses in SNI TLS extension on platforms with OpenSSL 1.0.2+ or inet_pton. Signed-off-by: Christian Heimes <christian@python.org>

Author: tiran

Misc/NEWS.d/next/Library/2017-12-20-09-25-10.bpo-32185.IL0cMt.rst

@@ -0,0 +1,2 @@
+The SSL module no longer sends IP addresses in SNI TLS extension on
+platforms with OpenSSL 1.0.2+ or inet_pton.

Modules/_ssl.c

@@ -55,6 +55,11 @@ static PySocketModule_APIObject PySocketModule;
 #include <sys/poll.h>
 #endif
 
+#ifndef MS_WINDOWS
+/* inet_pton */
+#include <arpa/inet.h>
+#endif
+
 /* Don't warn about deprecated functions */
 #ifdef __GNUC__
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
@@ -667,8 +672,41 @@ newPySSLSocket(PySSLContext *sslctx, PySocketSockObject *sock,
  SSL_set_mode(self->ssl, mode);
 
 #if HAVE_SNI
- if (server_hostname != NULL)
- SSL_set_tlsext_host_name(self->ssl, server_hostname);
+ if (server_hostname != NULL) {
+/* Don't send SNI for IP addresses. We cannot simply use inet_aton() and
+ * inet_pton() here. inet_aton() may be linked weakly and inet_pton() isn't
+ * available on all platforms. Use OpenSSL's IP address parser. It's
+ * available since 1.0.2 and LibreSSL since at least 2.3.0. */
+ int send_sni = 1;
+#if OPENSSL_VERSION_NUMBER >= 0x10200000L
+ ASN1_OCTET_STRING *ip = a2i_IPADDRESS(server_hostname);
+ if (ip == NULL) {
+ send_sni = 1;
+ ERR_clear_error();
+ } else {
+ send_sni = 0;
+ ASN1_OCTET_STRING_free(ip);
+ }
+#elif defined(HAVE_INET_PTON)
+#ifdef ENABLE_IPV6
+ char packed[Py_MAX(sizeof(struct in_addr), sizeof(struct in6_addr))];
+#else
+ char packed[sizeof(struct in_addr)];
+#endif /* ENABLE_IPV6 */
+ if (inet_pton(AF_INET, server_hostname, packed)) {
+ send_sni = 0;
+#ifdef ENABLE_IPV6
+ } else if(inet_pton(AF_INET6, server_hostname, packed)) {
+ send_sni = 0;
+#endif /* ENABLE_IPV6 */
+ } else {
+ send_sni = 1;
+ }
+#endif /* HAVE_INET_PTON */
+ if (send_sni) {
+ SSL_set_tlsext_host_name(self->ssl, server_hostname);
+ }
+ }
 #endif
 
  /* If the socket is in non-blocking mode or timeout mode, set the BIO