From 51938a8b731740299fe47d132b8840edba4141bc Mon Sep 17 00:00:00 2001

From: Robbie Harwood <rharwood@redhat.com>

Date: Sat, 29 May 2021 12:05:49 -0400

Subject: [PATCH] Fix k5tls module for OpenSSL 3

Starting in OpenSSL 3, connection termination without a close_notify

alert causes SSL_read() to return SSL_ERROR_SSL instead of

SSL_ERROR_SYSCALL.  OpenSSL 3 also provides a new option

SSL_OP_IGNORE_UNEXPECTED_EOF which allows an application to explicitly

ignore possible truncation attacks and receive SSL_ERROR_ZERO_RETURN

instead.

Remove the call to SSL_CTX_get_options() since SSL_CTX_set_options()

doesn't clear existing options.

[ghudson@mit.edu: edited commit message and comment]

(cherry picked from commit aa9b4a2a64046afd2fab7cb49c346295874a5fb6)

(cherry picked from commit 201e38845e9f70234bcaa9ba7c25b28e38169b0a)

---

 src/plugins/tls/k5tls/openssl.c | 17 ++++++++++++++---

 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/plugins/tls/k5tls/openssl.c b/src/plugins/tls/k5tls/openssl.c

index 76a43b3cd..99fda7ffc 100644

--- a/src/plugins/tls/k5tls/openssl.c

+++ b/src/plugins/tls/k5tls/openssl.c

@@ -433,7 +433,7 @@ setup(krb5_context context, SOCKET fd, const char *servername,

       char **anchors, k5_tls_handle *handle_out)

 {

     int e;

-    long options;

+    long options = SSL_OP_NO_SSLv2;

     SSL_CTX *ctx = NULL;

     SSL *ssl = NULL;

     k5_tls_handle handle = NULL;

@@ -448,8 +448,19 @@ setup(krb5_context context, SOCKET fd, const char *servername,

     ctx = SSL_CTX_new(SSLv23_client_method());

     if (ctx == NULL)

         goto error;

-    options = SSL_CTX_get_options(ctx);

-    SSL_CTX_set_options(ctx, options | SSL_OP_NO_SSLv2);

+

+#ifdef SSL_OP_IGNORE_UNEXPECTED_EOF

+    /*

+     * For OpenSSL 3 and later, mark close_notify alerts as optional.  We don't

+     * need to worry about truncation attacks because the protocols this module

+     * is used with (Kerberos and change-password) receive a single

+     * length-delimited message from the server.  For prior versions of OpenSSL

+     * we check for SSL_ERROR_SYSCALL when reading instead (this error changes

+     * to SSL_ERROR_SSL in OpenSSL 3).

+     */

+    options |= SSL_OP_IGNORE_UNEXPECTED_EOF;

+#endif

+    SSL_CTX_set_options(ctx, options);

     SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER, verify_callback);

     X509_STORE_set_flags(SSL_CTX_get_cert_store(ctx), 0);