Setup better defaults for OpenSSL ciphers

dbussink · Edward Thomson · commit c1ec732f4634 · 2016-04-11T15:58:56.000-04:00
This ensures that when using OpenSSL a safe default set of ciphers is selected. This is done so that the client communicates securely and we don't accidentally enable unsafe ciphers like RC4, or even worse some old export ciphers. Implements the first part of libgit2#3682
diff --git a/include/git2/common.h b/include/git2/common.h
@@ -149,6 +149,7 @@ typedef enum {
 	GIT_OPT_SET_SSL_CERT_LOCATIONS,
 	GIT_OPT_SET_USER_AGENT,
 	GIT_OPT_ENABLE_STRICT_OBJECT_CREATION,
+	GIT_OPT_SET_SSL_CIPHERS,
 } git_libgit2_opt_t;
 
 /**
@@ -260,6 +261,11 @@ typedef enum {
  *		> example, when this is enabled, the parent(s) and tree inputs
  *		> will be validated when creating a new commit.  This defaults
  *		> to disabled.
+ *	* opts(GIT_OPT_SET_SSL_CIPHERS, const char *ciphers)
+ *
+ *		> Set the SSL ciphers use for HTTPS connections.
+ *		>
+ *		> - `ciphers` is the list of ciphers that are eanbled.
  *
  * @param option Option key
  * @param ... value to set the option
diff --git a/src/global.c b/src/global.c
@@ -27,6 +27,7 @@ static git_global_shutdown_fn git__shutdown_callbacks[MAX_SHUTDOWN_CB];
 static git_atomic git__n_shutdown_callbacks;
 static git_atomic git__n_inits;
 char *git__user_agent;
+char *git__ssl_ciphers;
 
 void git__on_shutdown(git_global_shutdown_fn callback)
 {
@@ -83,6 +84,7 @@ static void shutdown_common(void)
 	}
 
 	git__free(git__user_agent);
+	git__free(git__ssl_ciphers);
 
 #if defined(GIT_MSVC_CRTDBG)
 	git_win32__crtdbg_stacktrace_cleanup();
diff --git a/src/global.h b/src/global.h
@@ -36,5 +36,6 @@ extern void git__on_shutdown(git_global_shutdown_fn callback);
 extern void git__free_tls_data(void);
 
 extern const char *git_libgit2__user_agent(void);
+extern const char *git_libgit2__ssl_ciphers(void);
 
 #endif
diff --git a/src/openssl_stream.c b/src/openssl_stream.c
@@ -34,6 +34,8 @@
 
 SSL_CTX *git__ssl_ctx;
 
+#define GIT_SSL_DEFAULT_CIPHERS "ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-DSS-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA:DHE-DSS-AES128-SHA256:DHE-DSS-AES256-SHA256:DHE-DSS-AES128-SHA:DHE-DSS-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA"
+
 #ifdef GIT_THREADS
 
 static git_mutex *openssl_locks;
@@ -85,6 +87,7 @@ int git_openssl_stream_global_init(void)
 {
 #ifdef GIT_OPENSSL
 	long ssl_opts = SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3;
+	const char *ciphers = git_libgit2__ssl_ciphers();
 
 	/* Older OpenSSL and MacOS OpenSSL doesn't have this */
 #ifdef SSL_OP_NO_COMPRESSION
@@ -108,6 +111,16 @@ int git_openssl_stream_global_init(void)
 		git__ssl_ctx = NULL;
 		return -1;
 	}
+
+	if (!ciphers) {
+		ciphers = GIT_SSL_DEFAULT_CIPHERS;
+	}
+
+	if(!SSL_CTX_set_cipher_list(git__ssl_ctx, ciphers)) {
+		SSL_CTX_free(git__ssl_ctx);
+		git__ssl_ctx = NULL;
+		return -1;
+	}
 #endif
 
 	git__on_shutdown(shutdown_ssl);
diff --git a/src/settings.c b/src/settings.c
@@ -71,12 +71,18 @@ static int config_level_to_sysdir(int config_level)
 }
 
 extern char *git__user_agent;
+extern char *git__ssl_ciphers;
 
 const char *git_libgit2__user_agent()
 {
 	return git__user_agent;
 }
 
+const char *git_libgit2__ssl_ciphers()
+{
+	return git__ssl_ciphers;
+}
+
 int git_libgit2_opts(int key, ...)
 {
 	int error = 0;
@@ -187,6 +193,22 @@ int git_libgit2_opts(int key, ...)
 		git_object__strict_input_validation = (va_arg(ap, int) != 0);
 		break;
 
+	case GIT_OPT_SET_SSL_CIPHERS:
+#ifdef GIT_OPENSSL
+		{
+			git__free(git__ssl_ciphers);
+			git__ssl_ciphers = git__strdup(va_arg(ap, const char *));
+			if (!git__ssl_ciphers) {
+				giterr_set_oom();
+				error = -1;
+			}
+		}
+#else
+		giterr_set(GITERR_NET, "Cannot set custom ciphers: OpenSSL is not enabled");
+		error = -1;
+#endif
+		break;
+
 	default:
 		giterr_set(GITERR_INVALID, "invalid option key");
 		error = -1;
diff --git a/tests/online/badssl.c b/tests/online/badssl.c
@@ -36,3 +36,12 @@ void test_online_badssl__self_signed(void)
 	cl_git_fail_with(GIT_ECERTIFICATE,
 			 git_clone(&g_repo, "https://self-signed.badssl.com/fake.git", "./fake", NULL));
 }
+
+void test_online_badssl__old_cipher(void)
+{
+	if (!g_has_ssl)
+		cl_skip();
+
+	cl_git_fail_with(GIT_ERROR,
+			 git_clone(&g_repo, "https://rc4.badssl.com/fake.git", "./fake", NULL));
+}

Original file line number	Diff line number	Diff line change
`@@ -27,6 +27,7 @@ static git_global_shutdown_fn git__shutdown_callbacks[MAX_SHUTDOWN_CB];`
`27`	`27`	`static git_atomic git__n_shutdown_callbacks;`
`28`	`28`	`static git_atomic git__n_inits;`
`29`	`29`	`char *git__user_agent;`
	`30`	`+char *git__ssl_ciphers;`
`30`	`31`
`31`	`32`	`void git__on_shutdown(git_global_shutdown_fn callback)`
`32`	`33`	`{`
`@@ -83,6 +84,7 @@ static void shutdown_common(void)`
`83`	`84`	`}`
`84`	`85`
`85`	`86`	`git__free(git__user_agent);`
	`87`	`+ git__free(git__ssl_ciphers);`
`86`	`88`
`87`	`89`	`#if defined(GIT_MSVC_CRTDBG)`
`88`	`90`	`git_win32__crtdbg_stacktrace_cleanup();`