From 40be3c926309867ebaeb4b1dcd7e1199473dea4d Mon Sep 17 00:00:00 2001
From: Artem Boldariev <artem@boldariev.com>
Date: Mon, 23 May 2022 13:41:06 +0300
Subject: [PATCH] Do not provide a shim for SSL_SESSION_is_resumable()

The recently added TLS client session cache used
SSL_SESSION_is_resumable() to avoid polluting the cache with
non-resumable sessions. However, it turned out that we cannot provide
a shim for this function across the whole range of OpenSSL versions
due to the fact that OpenSSL 1.1.0 does uses opaque pointers for
SSL_SESSION objects.

The commit replaces the shim for SSL_SESSION_is_resumable() with a non
public approximation of it on systems shipped with OpenSSL 1.1.0. It
is not turned into a proper shim because it does not fully emulate the
behaviour of SSL_SESSION_is_resumable(), but in our case it is good
enough, as it still helps to protect the cache from pollution.

For systems shipped with OpenSSL 1.0.X and derivatives (e.g. older
versions of LibreSSL), the provided replacement perfectly mimics the
function it is intended to replace.
---
 lib/isc/openssl_shim.c |  8 --------
 lib/isc/openssl_shim.h |  5 -----
 lib/isc/tls.c          | 29 ++++++++++++++++++++++++++++-
 3 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/lib/isc/openssl_shim.c b/lib/isc/openssl_shim.c
index 040fc68fbb..c39ba8c682 100644
--- a/lib/isc/openssl_shim.c
+++ b/lib/isc/openssl_shim.c
@@ -196,11 +196,3 @@ SSL_CTX_up_ref(SSL_CTX *ctx) {
 	return (CRYPTO_add(&ctx->references, 1, CRYPTO_LOCK_SSL_CTX) > 0);
 }
 #endif /* !HAVE_SSL_CTX_UP_REF */
-
-#if !HAVE_SSL_SESSION_IS_RESUMABLE
-int
-SSL_SESSION_is_resumable(const SSL_SESSION *sess) {
-	return (!sess->not_resumable &&
-		(sess->session_id_length > 0 || sess->tlsext_ticklen > 0));
-}
-#endif /* HAVE_SSL_SESSION_IS_RESUMABLE */
diff --git a/lib/isc/openssl_shim.h b/lib/isc/openssl_shim.h
index 6b3a30b288..b2916e20a9 100644
--- a/lib/isc/openssl_shim.h
+++ b/lib/isc/openssl_shim.h
@@ -135,8 +135,3 @@ SSL_CTX_set1_cert_store(SSL_CTX *ctx, X509_STORE *store);
 int
 SSL_CTX_up_ref(SSL_CTX *store);
 #endif /* !HAVE_SSL_CTX_UP_REF */
-
-#if !HAVE_SSL_SESSION_IS_RESUMABLE
-int
-SSL_SESSION_is_resumable(const SSL_SESSION *s);
-#endif /* HAVE_SSL_SESSION_IS_RESUMABLE */
diff --git a/lib/isc/tls.c b/lib/isc/tls.c
index 84b3330e7b..29cd063246 100644
--- a/lib/isc/tls.c
+++ b/lib/isc/tls.c
@@ -1484,6 +1484,33 @@ isc_tlsctx_client_session_cache_detach(
 	isc_mem_putanddetach(&cache->mctx, cache, sizeof(*cache));
 }
 
+static bool
+ssl_session_seems_resumable(const SSL_SESSION *sess) {
+#ifdef HAVE_SSL_SESSION_IS_RESUMABLE
+	/*
+	 * If SSL_SESSION_is_resumable() is available, let's use that. It
+	 * is expected to be available on OpenSSL >= 1.1.1 and its modern
+	 * siblings.
+	 */
+	return (SSL_SESSION_is_resumable(sess) != 0);
+#elif (OPENSSL_VERSION_NUMBER >= 0x10100000L)
+	/*
+	 * Taking into consideration that OpenSSL 1.1.0 uses opaque
+	 * pointers for SSL_SESSION, we cannot implement a replacement for
+	 * SSL_SESSION_is_resumable() manually. Let's use a sensible
+	 * approximation for that, then: if there is an associated session
+	 * ticket or session ID, then, most likely, the session is
+	 * resumable.
+	 */
+	unsigned int session_id_len = 0;
+	(void)SSL_SESSION_get_id(sess, &session_id_len);
+	return (SSL_SESSION_has_ticket(sess) || session_id_len > 0);
+#else
+	return (!sess->not_resumable &&
+		(sess->session_id_length > 0 || sess->tlsext_ticklen > 0));
+#endif
+}
+
 void
 isc_tlsctx_client_session_cache_keep(isc_tlsctx_client_session_cache_t *cache,
 				     char *remote_peer_name, isc_tls_t *tls) {
@@ -1500,7 +1527,7 @@ isc_tlsctx_client_session_cache_keep(isc_tlsctx_client_session_cache_t *cache,
 	sess = SSL_get1_session(tls);
 	if (sess == NULL) {
 		return;
-	} else if (SSL_SESSION_is_resumable(sess) == 0) {
+	} else if (!ssl_session_seems_resumable(sess)) {
 		SSL_SESSION_free(sess);
 		return;
 	}