[Openvpn-devel,(2.4)] Fix --tls-version-min and --tls-version-max for OpenSSL 1.1+

Message ID 20180120094228.13285-1-steffan@karger.me
State Accepted
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Series
  • [Openvpn-devel,(2.4)] Fix --tls-version-min and --tls-version-max for OpenSSL 1.1+
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Commit Message

Steffan Karger Jan. 20, 2018, 9:42 a.m.
As described in <80e6b449-c536-dc87-7215-3693872bce5a@birkenwald.de> on
the openvpn-devel mailing list, --tls-version-min no longer works with
OpenSSL 1.1.  Kurt Roeckx posted in a debian bug report:

"This is marked as important because if you switch to openssl 1.1.0
the defaults minimum version in Debian is currently TLS 1.2 and
you can't override it with the options that you're currently using
(and are deprecated)."

This patch is loosely based on the original patch by Kurt, but solves the
issue by adding functions to openssl-compat.h, like we also did for all
other openssl 1.1. breakage.  This results in not having to add more ifdefs
in ssl_openssl.c and thus cleaner code.

Signed-off-by: Steffan Karger <steffan@karger.me>
---
Note: This is cherry-pick to release/2.4 of the v4 patch for master.
      Tested to compile and work against OpenSSL 0.9.8 (for as far as
      possible; 0.9.8 only does TLS 1.0).

 src/openvpn/openssl_compat.h |  67 ++++++++++++++++++++++++++++
 src/openvpn/ssl.c            |   5 ++-
 src/openvpn/ssl_backend.h    |   4 +-
 src/openvpn/ssl_mbedtls.c    |   3 +-
 src/openvpn/ssl_openssl.c    | 102 +++++++++++++++++++++++++++----------------
 5 files changed, 141 insertions(+), 40 deletions(-)

Comments

Gert Doering Jan. 20, 2018, 11:26 a.m. | #1
ACK (compared the patches, only difference is the SSL_OP_NO_COMPRESSION
#ifdef).  So I take the ACK from Selva, on the base patch, and add my
ACK for "the 2.4 modifications make sense".  Haven't tested on an 0.9.8 
system yet.

for patchwork:

Acked-by: Gert Doering <gert@greenie.muc.de>

Your patch has been applied to the release/2.4 branch.

commit a25a278c1ccdbfd9ca06f60f2cc4cf2436269854
Author: Steffan Karger
Date:   Sat Jan 20 10:42:28 2018 +0100

     Fix --tls-version-min and --tls-version-max for OpenSSL 1.1+

     Signed-off-by: Steffan Karger <steffan@karger.me>
     Acked-by: Selva Nair <selva.nair@gmail.com>
     Acked-by: Gert Doering <gert@greenie.muc.de>
     Message-Id: <20180120094228.13285-1-steffan@karger.me>
     URL: https://www.mail-archive.com/search?l=mid&q=20180120094228.13285-1-steffan@karger.me
     Signed-off-by: Gert Doering <gert@greenie.muc.de>
     (cherry picked with 2.4 amendments from commit 0e8a30c0b05c1e2b59a1dea0a6eab5daa1d9d9a1)

--
kind regards,

Gert Doering


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Patch

diff --git a/src/openvpn/openssl_compat.h b/src/openvpn/openssl_compat.h
index 05ec4e95..9f1e92a1 100644
--- a/src/openvpn/openssl_compat.h
+++ b/src/openvpn/openssl_compat.h
@@ -661,4 +661,71 @@  EC_GROUP_order_bits(const EC_GROUP *group)
 #define RSA_F_RSA_OSSL_PRIVATE_ENCRYPT       RSA_F_RSA_EAY_PRIVATE_ENCRYPT
 #endif
 
+#ifndef SSL_CTX_get_min_proto_version
+/** Dummy SSL_CTX_get_min_proto_version for OpenSSL < 1.1 (not really needed) */
+static inline int
+SSL_CTX_get_min_proto_version(SSL_CTX *ctx)
+{
+    return 0;
+}
+#endif /* SSL_CTX_get_min_proto_version */
+
+#ifndef SSL_CTX_set_min_proto_version
+/** Mimics SSL_CTX_set_min_proto_version for OpenSSL < 1.1 */
+static inline int
+SSL_CTX_set_min_proto_version(SSL_CTX *ctx, long tls_ver_min)
+{
+    long sslopt = SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3; /* Never do < TLS 1.0 */
+
+    if (tls_ver_min > TLS1_VERSION)
+    {
+        sslopt |= SSL_OP_NO_TLSv1;
+    }
+#ifdef SSL_OP_NO_TLSv1_1
+    if (tls_ver_min > TLS1_1_VERSION)
+    {
+        sslopt |= SSL_OP_NO_TLSv1_1;
+    }
+#endif
+#ifdef SSL_OP_NO_TLSv1_2
+    if (tls_ver_min > TLS1_2_VERSION)
+    {
+        sslopt |= SSL_OP_NO_TLSv1_2;
+    }
+#endif
+    SSL_CTX_set_options(ctx, sslopt);
+
+    return 1;
+}
+#endif /* SSL_CTX_set_min_proto_version */
+
+#ifndef SSL_CTX_set_max_proto_version
+/** Mimics SSL_CTX_set_max_proto_version for OpenSSL < 1.1 */
+static inline int
+SSL_CTX_set_max_proto_version(SSL_CTX *ctx, long tls_ver_max)
+{
+    long sslopt = 0;
+
+    if (tls_ver_max < TLS1_VERSION)
+    {
+        sslopt |= SSL_OP_NO_TLSv1;
+    }
+#ifdef SSL_OP_NO_TLSv1_1
+    if (tls_ver_max < TLS1_1_VERSION)
+    {
+        sslopt |= SSL_OP_NO_TLSv1_1;
+    }
+#endif
+#ifdef SSL_OP_NO_TLSv1_2
+    if (tls_ver_max < TLS1_2_VERSION)
+    {
+        sslopt |= SSL_OP_NO_TLSv1_2;
+    }
+#endif
+    SSL_CTX_set_options(ctx, sslopt);
+
+    return 1;
+}
+#endif /* SSL_CTX_set_max_proto_version */
+
 #endif /* OPENSSL_COMPAT_H_ */
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index 08e4b121..0841cd09 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -624,7 +624,10 @@  init_ssl(const struct options *options, struct tls_root_ctx *new_ctx)
      * cipher restrictions before loading certificates */
     tls_ctx_restrict_ciphers(new_ctx, options->cipher_list);
 
-    tls_ctx_set_options(new_ctx, options->ssl_flags);
+    if (!tls_ctx_set_options(new_ctx, options->ssl_flags))
+    {
+        goto err;
+    }
 
     if (options->pkcs12_file)
     {
diff --git a/src/openvpn/ssl_backend.h b/src/openvpn/ssl_backend.h
index f588110c..bdef634a 100644
--- a/src/openvpn/ssl_backend.h
+++ b/src/openvpn/ssl_backend.h
@@ -164,8 +164,10 @@  bool tls_ctx_initialised(struct tls_root_ctx *ctx);
  *
  * @param ctx           TLS context to set options on
  * @param ssl_flags     SSL flags to set
+ *
+ * @return true on success, false otherwise.
  */
-void tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags);
+bool tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags);
 
 /**
  * Restrict the list of ciphers that can be used within the TLS context.
diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c
index 09829ebb..2752a4e0 100644
--- a/src/openvpn/ssl_mbedtls.c
+++ b/src/openvpn/ssl_mbedtls.c
@@ -206,9 +206,10 @@  key_state_export_keying_material(struct key_state_ssl *ssl,
 {
 }
 
-void
+bool
 tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags)
 {
+    return true;
 }
 
 static const char *
diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c
index 8338800e..5e869f2c 100644
--- a/src/openvpn/ssl_openssl.c
+++ b/src/openvpn/ssl_openssl.c
@@ -206,16 +206,65 @@  info_callback(INFO_CALLBACK_SSL_CONST SSL *s, int where, int ret)
 int
 tls_version_max(void)
 {
-#if defined(SSL_OP_NO_TLSv1_2)
+#if defined(TLS1_2_VERSION) || defined(SSL_OP_NO_TLSv1_2)
     return TLS_VER_1_2;
-#elif defined(SSL_OP_NO_TLSv1_1)
+#elif defined(TLS1_1_VERSION) || defined(SSL_OP_NO_TLSv1_1)
     return TLS_VER_1_1;
 #else
     return TLS_VER_1_0;
 #endif
 }
 
-void
+/** Convert internal version number to openssl version number */
+static int
+openssl_tls_version(int ver)
+{
+    if (ver == TLS_VER_1_0)
+    {
+        return TLS1_VERSION;
+    }
+    else if (ver == TLS_VER_1_1)
+    {
+        return TLS1_1_VERSION;
+    }
+    else if (ver == TLS_VER_1_2)
+    {
+        return TLS1_2_VERSION;
+    }
+    return 0;
+}
+
+static bool
+tls_ctx_set_tls_versions(struct tls_root_ctx *ctx, unsigned int ssl_flags)
+{
+    int tls_ver_min = openssl_tls_version(
+        (ssl_flags >> SSLF_TLS_VERSION_MIN_SHIFT) & SSLF_TLS_VERSION_MIN_MASK);
+    int tls_ver_max = openssl_tls_version(
+        (ssl_flags >> SSLF_TLS_VERSION_MAX_SHIFT) & SSLF_TLS_VERSION_MAX_MASK);
+
+    if (!tls_ver_min)
+    {
+        /* Enforce at least TLS 1.0 */
+        int cur_min = SSL_CTX_get_min_proto_version(ctx->ctx);
+        tls_ver_min = cur_min < TLS1_VERSION ? TLS1_VERSION : cur_min;
+    }
+
+    if (!SSL_CTX_set_min_proto_version(ctx->ctx, tls_ver_min))
+    {
+        msg(D_TLS_ERRORS, "%s: failed to set minimum TLS version", __func__);
+        return false;
+    }
+
+    if (tls_ver_max && !SSL_CTX_set_max_proto_version(ctx->ctx, tls_ver_max))
+    {
+        msg(D_TLS_ERRORS, "%s: failed to set maximum TLS version", __func__);
+        return false;
+    }
+
+    return true;
+}
+
+bool
 tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags)
 {
     ASSERT(NULL != ctx);
@@ -223,44 +272,21 @@  tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags)
     /* default certificate verification flags */
     int flags = SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT;
 
-    /* process SSL options including minimum TLS version we will accept from peer */
-    {
-        long sslopt = SSL_OP_SINGLE_DH_USE | SSL_OP_NO_TICKET | SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3;
-        int tls_ver_max = TLS_VER_UNSPEC;
-        const int tls_ver_min =
-            (ssl_flags >> SSLF_TLS_VERSION_MIN_SHIFT) & SSLF_TLS_VERSION_MIN_MASK;
-
-        tls_ver_max =
-            (ssl_flags >> SSLF_TLS_VERSION_MAX_SHIFT) & SSLF_TLS_VERSION_MAX_MASK;
-        if (tls_ver_max <= TLS_VER_UNSPEC)
-        {
-            tls_ver_max = tls_version_max();
-        }
-
-        if (tls_ver_min > TLS_VER_1_0 || tls_ver_max < TLS_VER_1_0)
-        {
-            sslopt |= SSL_OP_NO_TLSv1;
-        }
-#ifdef SSL_OP_NO_TLSv1_1
-        if (tls_ver_min > TLS_VER_1_1 || tls_ver_max < TLS_VER_1_1)
-        {
-            sslopt |= SSL_OP_NO_TLSv1_1;
-        }
-#endif
-#ifdef SSL_OP_NO_TLSv1_2
-        if (tls_ver_min > TLS_VER_1_2 || tls_ver_max < TLS_VER_1_2)
-        {
-            sslopt |= SSL_OP_NO_TLSv1_2;
-        }
-#endif
+    /* process SSL options */
+    long sslopt = SSL_OP_SINGLE_DH_USE | SSL_OP_NO_TICKET;
 #ifdef SSL_OP_CIPHER_SERVER_PREFERENCE
-        sslopt |= SSL_OP_CIPHER_SERVER_PREFERENCE;
+    sslopt |= SSL_OP_CIPHER_SERVER_PREFERENCE;
 #endif
 #ifdef SSL_OP_NO_COMPRESSION
-        /* Disable compression - flag not available in OpenSSL 0.9.8 */
-        sslopt |= SSL_OP_NO_COMPRESSION;
+    /* Disable compression - flag not available in OpenSSL 0.9.8 */
+    sslopt |= SSL_OP_NO_COMPRESSION;
 #endif
-        SSL_CTX_set_options(ctx->ctx, sslopt);
+
+    SSL_CTX_set_options(ctx->ctx, sslopt);
+
+    if (!tls_ctx_set_tls_versions(ctx, ssl_flags))
+    {
+        return false;
     }
 
 #ifdef SSL_MODE_RELEASE_BUFFERS
@@ -283,6 +309,8 @@  tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags)
     SSL_CTX_set_verify(ctx->ctx, flags, verify_callback);
 
     SSL_CTX_set_info_callback(ctx->ctx, info_callback);
+
+    return true;
 }
 
 void