[openssl-dev] SSL_set_tlsext_host_name(ssl, "")

[Viktor Dukhovni]

On Sat, Jan 16, 2016 at 09:42:18AM -0800, Claus Assmann wrote:

> While playing around with the DANE suppport in OpenSSL 1.1

Thanks for the test drive.

> I noticed that the TLS handshake will fail if I specify an empty name:
> SSL_dane_enable(ssl, "")

Good catch.

> (AFAICT no name is needed for DANE-TA(2) RRs).

DANE requires the client to send SNI in all cases.  The server will
often ignore the SNI name if it has just one certificate.

> This can also be reproduced using
> openssl s_client -servername "" ...

Please try the two attached patches.

-- 
	Viktor.
-------------- next part --------------
>From c9f8d6dc5c37988ec5c721356b3e287a6d491c55 Mon Sep 17 00:00:00 2001
From: Viktor Dukhovni <openssl-users at dukhovni.org>
Date: Sat, 16 Jan 2016 12:57:24 -0500
Subject: [PATCH 1/2] Empty SNI names are not valid

While empty inputs to SSL_set1_host() clear the reference identifier
list.
---
 crypto/x509/x509_vpm.c | 4 ++--
 ssl/s3_lib.c           | 5 ++++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/crypto/x509/x509_vpm.c b/crypto/x509/x509_vpm.c
index 827360d..b596d84 100644
--- a/crypto/x509/x509_vpm.c
+++ b/crypto/x509/x509_vpm.c
@@ -92,11 +92,11 @@ static int int_x509_param_set_hosts(X509_VERIFY_PARAM *vpm, int mode,
      * Refuse names with embedded NUL bytes, except perhaps as final byte.
      * XXX: Do we need to push an error onto the error stack?
      */
-    if (namelen == 0)
+    if (namelen == 0 || name == NULL)
         namelen = name ? strlen(name) : 0;
     else if (name && memchr(name, '\0', namelen > 1 ? namelen - 1 : namelen))
         return 0;
-    if (name && name[namelen - 1] == '\0')
+    if (name != NULL && name[namelen - 1] == '\0')
         --namelen;
 
     if (mode == SET_HOST) {
diff --git a/ssl/s3_lib.c b/ssl/s3_lib.c
index de8dae2..54b8eba 100644
--- a/ssl/s3_lib.c
+++ b/ssl/s3_lib.c
@@ -3534,13 +3534,16 @@ long ssl3_ctrl(SSL *s, int cmd, long larg, void *parg)
 #endif                          /* !OPENSSL_NO_EC */
     case SSL_CTRL_SET_TLSEXT_HOSTNAME:
         if (larg == TLSEXT_NAMETYPE_host_name) {
+            size_t len;
+
             OPENSSL_free(s->tlsext_hostname);
             s->tlsext_hostname = NULL;
 
             ret = 1;
             if (parg == NULL)
                 break;
-            if (strlen((char *)parg) > TLSEXT_MAXLEN_host_name) {
+            len = strlen((char *)parg);
+            if (len == 0 || len > TLSEXT_MAXLEN_host_name) {
                 SSLerr(SSL_F_SSL3_CTRL, SSL_R_SSL3_EXT_INVALID_SERVERNAME);
                 return 0;
             }
-- 
2.5.4 (Apple Git-61)

-------------- next part --------------
>From 8fc1c14db18d000437664d81e4e250d44179bdc0 Mon Sep 17 00:00:00 2001
From: Viktor Dukhovni <openssl-users at dukhovni.org>
Date: Sat, 16 Jan 2016 13:25:17 -0500
Subject: [PATCH 2/2] Better invalid SNI name error handling

Also report an SSL_dane_enable error when the basedomain is an
invalid SNI name.  Avoid side-effects when such a name is valid
with X509_VERIFY_PARAM_set1_host(), as e.g. with an empty name, by
setting the SNI name first.
---
 ssl/ssl_lib.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index 90de747..e922e3f 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -872,18 +872,24 @@ int SSL_dane_enable(SSL *s, const char *basedomain)
         return 0;
     }
 
+    /*
+     * Default SNI name.  This rejects empty names, while set1_host below
+     * accepts them and disables host name checks.  To avoid side-effects with
+     * invalid input, set the SNI name first.
+     */
+    if (s->tlsext_hostname == NULL) {
+	if (!SSL_set_tlsext_host_name(s, basedomain)) {
+            SSLerr(SSL_F_SSL_DANE_ENABLE, SSL_R_ERROR_SETTING_TLSA_BASE_DOMAIN);
+	    return -1;
+        }
+    }
+
     /* Primary RFC6125 reference identifier */
     if (!X509_VERIFY_PARAM_set1_host(s->param, basedomain, 0)) {
         SSLerr(SSL_F_SSL_DANE_ENABLE, SSL_R_ERROR_SETTING_TLSA_BASE_DOMAIN);
         return -1;
     }
 
-    /* Default SNI name */
-    if (s->tlsext_hostname == NULL) {
-	if (!SSL_set_tlsext_host_name(s, basedomain))
-	    return -1;
-    }
-
     dane->mdpth = -1;
     dane->pdpth = -1;
     dane->dctx = &s->ctx->dane;
-- 
2.5.4 (Apple Git-61)