Merge pull request #4173 from tiennou/mbedtls

mbedTLS support

.travis.yml

@@ -55,6 +55,16 @@ matrix:
          OPTIONS="-DBUILD_CLAR=ON -DBUILD_EXAMPLES=OFF -DDEBUG_POOL=ON -DCMAKE_BUILD_TYPE=Debug"
      os: linux
      dist: trusty
+   - compiler: gcc
+     env:
+         MBEDTLS=1
+         OPTIONS="-DTHREADSAFE=ON -DCMAKE_BUILD_TYPE=Release -DUSE_HTTPS=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
+     os: linux
+   - compiler: gcc
+     env:
+         MBEDTLS=1
+         OPTIONS="-DTHREADSAFE=OFF -DBUILD_EXAMPLES=ON -DUSE_HTTPS=mbedTLS -DMBEDTLS_ROOT_DIR=../deps/mbedtls"
+     os: linux
  allow_failures:
    - env: COVERITY=1
 

CMakeLists.txt

@@ -48,7 +48,7 @@ OPTION( PROFILE				"Generate profiling information"		OFF )
 OPTION( ENABLE_TRACE		"Enables tracing support"				OFF )
 OPTION( LIBGIT2_FILENAME	"Name of the produced binary"			OFF )
 
-SET(SHA1_BACKEND "CollisionDetection" CACHE STRING "Backend to use for SHA1. One of Generic, OpenSSL, Win32, CommonCrypto, CollisionDetection. ")
+SET(SHA1_BACKEND "CollisionDetection" CACHE STRING "Backend to use for SHA1. One of Generic, OpenSSL, Win32, CommonCrypto, mbedTLS, CollisionDetection. ")
 OPTION( USE_SSH				"Link with libssh to enable SSH support" ON )
 OPTION( USE_HTTPS			"Enable HTTPS support. Can be set to a specific backend"	ON )
 OPTION( USE_GSSAPI			"Link with libgssapi for SPNEGO auth"   OFF )

cmake/Modules/FindmbedTLS.cmake

+# - Try to find mbedTLS
+# Once done this will define
+#
+# Read-Only variables
+#  MBEDTLS_FOUND - system has mbedTLS
+#  MBEDTLS_INCLUDE_DIR - the mbedTLS include directory
+#  MBEDTLS_LIBRARY_DIR - the mbedTLS library directory
+#  MBEDTLS_LIBRARIES - Link these to use mbedTLS
+#  MBEDTLS_LIBRARY - path to mbedTLS library
+#  MBEDX509_LIBRARY - path to mbedTLS X.509 library
+#  MBEDCRYPTO_LIBRARY - path to mbedTLS Crypto library
+#
+# Hint
+#  MBEDTLS_ROOT_DIR can be pointed to a local mbedTLS installation.
+
+SET(_MBEDTLS_ROOT_HINTS
+    ${MBEDTLS_ROOT_DIR}
+    ENV MBEDTLS_ROOT_DIR
+)
+
+SET(_MBEDTLS_ROOT_HINTS_AND_PATHS
+    HINTS ${_MBEDTLS_ROOT_HINTS}
+    PATHS ${_MBEDTLS_ROOT_PATHS}
+)
+
+FIND_PATH(MBEDTLS_INCLUDE_DIR
+    NAMES mbedtls/version.h
+    ${_MBEDTLS_ROOT_HINTS_AND_PATHS}
+    PATH_SUFFIXES include
+)
+
+IF(MBEDTLS_INCLUDE_DIR AND MBEDTLS_LIBRARIES)
+    # Already in cache, be silent
+    SET(MBEDTLS_FIND_QUIETLY TRUE)
+ENDIF()
+
+FIND_LIBRARY(MBEDTLS_LIBRARY
+    NAMES mbedtls libmbedtls
+    ${_MBEDTLS_ROOT_HINTS_AND_PATHS}
+    PATH_SUFFIXES library
+)
+FIND_LIBRARY(MBEDX509_LIBRARY
+    NAMES mbedx509 libmbedx509
+    ${_MBEDTLS_ROOT_HINTS_AND_PATHS}
+    PATH_SUFFIXES library
+)
+FIND_LIBRARY(MBEDCRYPTO_LIBRARY
+    NAMES mbedcrypto libmbedcrypto
+    ${_MBEDTLS_ROOT_HINTS_AND_PATHS}
+    PATH_SUFFIXES library
+)
+
+IF(MBEDTLS_INCLUDE_DIR AND MBEDTLS_LIBRARY AND MBEDX509_LIBRARY AND MBEDCRYPTO_LIBRARY)
+     SET(MBEDTLS_FOUND TRUE)
+ENDIF()
+
+IF(MBEDTLS_FOUND)
+    # split mbedTLS into -L and -l linker options, so we can set them for pkg-config
+    GET_FILENAME_COMPONENT(MBEDTLS_LIBRARY_DIR ${MBEDTLS_LIBRARY} PATH)
+    GET_FILENAME_COMPONENT(MBEDTLS_LIBRARY_FILE ${MBEDTLS_LIBRARY} NAME_WE)
+    GET_FILENAME_COMPONENT(MBEDX509_LIBRARY_FILE ${MBEDX509_LIBRARY} NAME_WE)
+    GET_FILENAME_COMPONENT(MBEDCRYPTO_LIBRARY_FILE ${MBEDCRYPTO_LIBRARY} NAME_WE)
+    STRING(REGEX REPLACE "^lib" "" MBEDTLS_LIBRARY_FILE ${MBEDTLS_LIBRARY_FILE})
+    STRING(REGEX REPLACE "^lib" "" MBEDX509_LIBRARY_FILE ${MBEDX509_LIBRARY_FILE})
+    STRING(REGEX REPLACE "^lib" "" MBEDCRYPTO_LIBRARY_FILE ${MBEDCRYPTO_LIBRARY_FILE})
+    SET(MBEDTLS_LIBRARIES "-L${MBEDTLS_LIBRARY_DIR} -l${MBEDTLS_LIBRARY_FILE} -l${MBEDX509_LIBRARY_FILE} -l${MBEDCRYPTO_LIBRARY_FILE}")
+
+    IF(NOT MBEDTLS_FIND_QUIETLY)
+        MESSAGE(STATUS "Found mbedTLS:")
+        FILE(READ ${MBEDTLS_INCLUDE_DIR}/mbedtls/version.h MBEDTLSCONTENT)
+        STRING(REGEX MATCH "MBEDTLS_VERSION_STRING +\"[0-9|.]+\"" MBEDTLSMATCH ${MBEDTLSCONTENT})
+        IF (MBEDTLSMATCH)
+            STRING(REGEX REPLACE "MBEDTLS_VERSION_STRING +\"([0-9|.]+)\"" "\\1" MBEDTLS_VERSION ${MBEDTLSMATCH})
+            MESSAGE(STATUS "  version ${MBEDTLS_VERSION}")
+        ENDIF(MBEDTLSMATCH)
+        MESSAGE(STATUS "  TLS: ${MBEDTLS_LIBRARY}")
+        MESSAGE(STATUS "  X509: ${MBEDX509_LIBRARY}")
+        MESSAGE(STATUS "  Crypto: ${MBEDCRYPTO_LIBRARY}")
+    ENDIF(NOT MBEDTLS_FIND_QUIETLY)
+ELSE(MBEDTLS_FOUND)
+    IF(MBEDTLS_FIND_REQUIRED)
+        MESSAGE(FATAL_ERROR "Could not find mbedTLS")
+    ENDIF(MBEDTLS_FIND_REQUIRED)
+ENDIF(MBEDTLS_FOUND)
+
+MARK_AS_ADVANCED(
+    MBEDTLS_INCLUDE_DIR
+    MBEDTLS_LIBRARY_DIR
+    MBEDTLS_LIBRARIES
+    MBEDTLS_LIBRARY
+    MBEDX509_LIBRARY
+    MBEDCRYPTO_LIBRARY
+)

script/install-deps-linux.sh

+#!/bin/sh
+
+set -x
+
+if [ "$MBEDTLS" ]; then
+  git clone --depth 10 --single-branch --branch mbedtls-2.6.1 https://github.com/ARMmbed/mbedtls.git ./deps/mbedtls
+  cd ./deps/mbedtls
+  # We pass -fPIC explicitely because we'll include it in libgit2.so
+  CFLAGS=-fPIC cmake -DENABLE_PROGRAMS=OFF -DENABLE_TESTING=OFF -DUSE_SHARED_MBEDTLS_LIBRARY=OFF -DUSE_STATIC_MBEDTLS_LIBRARY=ON .
+  cmake --build .
+
+  echo "mbedTLS built in `pwd`"
+fi

src/CMakeLists.txt

@@ -133,6 +133,9 @@ ELSE ()
 ENDIF()
 
 IF (USE_HTTPS)
+	# We try to find any packages our backends might use
+	FIND_PACKAGE(OpenSSL)
+	FIND_PACKAGE(mbedTLS)
 	IF (CMAKE_SYSTEM_NAME MATCHES "Darwin")
 		FIND_PACKAGE(Security)
 		FIND_PACKAGE(CoreFoundation)
@@ -149,8 +152,13 @@ IF (USE_HTTPS)
 			ENDIF()
 		ELSEIF (WINHTTP)
 			SET(HTTPS_BACKEND "WinHTTP")
-		ELSE()
+		ELSEIF(OPENSSL_FOUND)
 			SET(HTTPS_BACKEND "OpenSSL")
+		ELSEIF(MBEDTLS_FOUND)
+			SET(HTTPS_BACKEND "mbedTLS")
+		ELSE()
+			MESSAGE(FATAL_ERROR "Unable to autodetect a usable HTTPS backend."
+				"Please pass the backend name explicitly (-DUSE_HTTPS=backend)")
 		ENDIF()
 	ELSE()
 		# Backend was explicitly set
@@ -174,8 +182,6 @@ IF (USE_HTTPS)
 		LIST(APPEND LIBGIT2_LIBS ${COREFOUNDATION_LIBRARIES} ${SECURITY_LIBRARIES})
 		LIST(APPEND LIBGIT2_PC_LIBS ${COREFOUNDATION_LDFLAGS} ${SECURITY_LDFLAGS})
 	ELSEIF (HTTPS_BACKEND STREQUAL "OpenSSL")
-		FIND_PACKAGE(OpenSSL)
-
 		IF (NOT OPENSSL_FOUND)
 			MESSAGE(FATAL_ERROR "Asked for OpenSSL TLS backend, but it wasn't found")
 		ENDIF()
@@ -185,6 +191,53 @@ IF (USE_HTTPS)
 		LIST(APPEND LIBGIT2_LIBS ${OPENSSL_LIBRARIES})
 		LIST(APPEND LIBGIT2_PC_LIBS ${OPENSSL_LDFLAGS})
 		LIST(APPEND LIBGIT2_PC_REQUIRES "openssl")
+	ELSEIF(HTTPS_BACKEND STREQUAL "mbedTLS")
+		IF (NOT MBEDTLS_FOUND)
+			MESSAGE(FATAL_ERROR "Asked for mbedTLS backend, but it wasn't found")
+		ENDIF()
+
+		IF(NOT CERT_LOCATION)
+			MESSAGE("Auto-detecting default certificates location")
+			IF(CMAKE_SYSTEM_NAME MATCHES Darwin)
+				# Check for an Homebrew installation
+				SET(OPENSSL_CMD "/usr/local/opt/openssl/bin/openssl")
+			ELSE()
+				SET(OPENSSL_CMD "openssl")
+			ENDIF()
+			EXECUTE_PROCESS(COMMAND ${OPENSSL_CMD} version -d OUTPUT_VARIABLE OPENSSL_DIR OUTPUT_STRIP_TRAILING_WHITESPACE)
+			IF(OPENSSL_DIR)
+				STRING(REGEX REPLACE "^OPENSSLDIR: \"(.*)\"$" "\\1/" OPENSSL_DIR ${OPENSSL_DIR})
+
+				SET(OPENSSL_CA_LOCATIONS
+					"ca-bundle.pem"             # OpenSUSE Leap 42.1
+					"cert.pem"                  # Ubuntu 14.04, FreeBSD
+					"certs/ca-certificates.crt" # Ubuntu 16.04
+					"certs/ca.pem"              # Debian 7
+				)
+				FOREACH(SUFFIX IN LISTS OPENSSL_CA_LOCATIONS)
+					SET(LOC "${OPENSSL_DIR}${SUFFIX}")
+					IF(NOT CERT_LOCATION AND EXISTS "${OPENSSL_DIR}${SUFFIX}")
+						SET(CERT_LOCATION ${LOC})
+					ENDIF()
+				ENDFOREACH()
+			ELSE()
+				MESSAGE("Unable to find OpenSSL executable. Please provide default certificate location via CERT_LOCATION")
+			ENDIF()
+		ENDIF()
+
+		IF(CERT_LOCATION)
+			IF(NOT EXISTS ${CERT_LOCATION})
+				MESSAGE(FATAL_ERROR "Cannot use CERT_LOCATION=${CERT_LOCATION} as it doesn't exist")
+			ENDIF()
+			ADD_FEATURE_INFO(CERT_LOCATION ON "using certificates from ${CERT_LOCATION}")
+			ADD_DEFINITIONS(-DGIT_DEFAULT_CERT_LOCATION="${CERT_LOCATION}")
+		ENDIF()
+
+		SET(GIT_MBEDTLS 1)
+		LIST(APPEND LIBGIT2_INCLUDES ${MBEDTLS_INCLUDE_DIR})
+		LIST(APPEND LIBGIT2_LIBS ${MBEDTLS_LIBRARIES})
+		LIST(APPEND LIBGIT2_PC_LIBS ${MBEDTLS_LDFLAGS})
+		LIST(APPEND LIBGIT2_PC_REQUIRES "mbedtls")
 	ELSEIF (HTTPS_BACKEND STREQUAL "WinHTTP")
 		# WinHTTP setup was handled in the WinHTTP-specific block above
 	ELSE()
@@ -230,6 +283,11 @@ ELSEIF(SHA1_BACKEND STREQUAL "Win32")
 ELSEIF(SHA1_BACKEND STREQUAL "CommonCrypto")
 	ADD_FEATURE_INFO(SHA ON "using CommonCrypto")
 	SET(GIT_SHA1_COMMON_CRYPTO 1)
+ELSEIF (SHA1_BACKEND STREQUAL "mbedTLS")
+	ADD_FEATURE_INFO(SHA ON "using mbedTLS")
+	SET(GIT_SHA1_MBEDTLS 1)
+	FILE(GLOB SRC_SHA1 src/hash/hash_mbedtls.c)
+	LIST(APPEND LIBGIT2_PC_REQUIRES "mbedtls")
 ELSE()
 	MESSAGE(FATAL_ERROR "Asked for unknown SHA1 backend ${SHA1_BACKEND}")
 ENDIF()

src/features.h.in

@@ -27,10 +27,12 @@
 #cmakedefine GIT_HTTPS 1
 #cmakedefine GIT_OPENSSL 1
 #cmakedefine GIT_SECURE_TRANSPORT 1
+#cmakedefine GIT_MBEDTLS 1
 
 #cmakedefine GIT_SHA1_COLLISIONDETECT 1
 #cmakedefine GIT_SHA1_WIN32 1
 #cmakedefine GIT_SHA1_COMMON_CRYPTO 1
 #cmakedefine GIT_SHA1_OPENSSL 1
+#cmakedefine GIT_SHA1_MBEDTLS 1
 
 #endif

src/global.c

@@ -12,6 +12,7 @@
 #include "filter.h"
 #include "merge_driver.h"
 #include "streams/curl.h"
+#include "streams/mbedtls.h"
 #include "streams/openssl.h"
 #include "thread-utils.h"
 #include "git2/global.h"
@@ -65,7 +66,8 @@ static int init_common(void)
 		(ret = git_merge_driver_global_init()) == 0 &&
 		(ret = git_transport_ssh_global_init()) == 0 &&
 		(ret = git_openssl_stream_global_init()) == 0 &&
-		(ret = git_curl_stream_global_init()) == 0)
+		(ret = git_curl_stream_global_init()) == 0 &&
+		(ret = git_mbedtls_stream_global_init()) == 0)
 		ret = git_mwindow_global_init();
 
 	GIT_MEMORY_BARRIER;

src/hash.h

@@ -26,6 +26,8 @@ void git_hash_ctx_cleanup(git_hash_ctx *ctx);
 # include "hash/hash_openssl.h"
 #elif defined(GIT_SHA1_WIN32)
 # include "hash/hash_win32.h"
+#elif defined(GIT_SHA1_MBEDTLS)
+# include "hash/hash_mbedtls.h"
 #else
 # include "hash/hash_generic.h"
 #endif

src/hash/hash_mbedtls.c

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "common.h"
+#include "hash.h"
+#include "hash/hash_mbedtls.h"
+
+void git_hash_ctx_cleanup(git_hash_ctx *ctx)
+{
+    assert(ctx);
+    mbedtls_sha1_free(&ctx->c);
+}
+
+int git_hash_init(git_hash_ctx *ctx)
+{
+    assert(ctx);
+    mbedtls_sha1_init(&ctx->c);
+    mbedtls_sha1_starts(&ctx->c);
+    return 0;
+}
+
+int git_hash_update(git_hash_ctx *ctx, const void *data, size_t len)
+{
+    assert(ctx);
+    mbedtls_sha1_update(&ctx->c, data, len);
+    return 0;
+}
+
+int git_hash_final(git_oid *out, git_hash_ctx *ctx)
+{
+    assert(ctx);
+    mbedtls_sha1_finish(&ctx->c, out->id);
+    return 0;
+}

src/hash/hash_mbedtls.h

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#ifndef INCLUDE_hash_mbedtld_h__
+#define INCLUDE_hash_mbedtld_h__
+
+#include <mbedtls/sha1.h>
+
+struct git_hash_ctx {
+    mbedtls_sha1_context c;
+};
+
+#define git_hash_global_init() 0
+#define git_hash_ctx_init(ctx) git_hash_init(ctx)
+
+#endif /* INCLUDE_hash_mbedtld_h__ */

src/settings.c

@@ -11,6 +11,10 @@
 # include <openssl/err.h>
 #endif
 
+#ifdef GIT_MBEDTLS
+# include <mbedtls/error.h>
+#endif
+
 #include <git2.h>
 #include "sysdir.h"
 #include "cache.h"
@@ -20,6 +24,7 @@
 #include "refs.h"
 #include "transports/smart.h"
 #include "streams/openssl.h"
+#include "streams/mbedtls.h"
 
 void git_libgit2_version(int *major, int *minor, int *rev)
 {
@@ -175,6 +180,15 @@ int git_libgit2_opts(int key, ...)
 			const char *path = va_arg(ap, const char *);
 			error = git_openssl__set_cert_location(file, path);
 		}
+#elif defined(GIT_MBEDTLS)
+		{
+			const char *file = va_arg(ap, const char *);
+			const char *path = va_arg(ap, const char *);
+			if (file)
+				error = git_mbedtls__set_cert_location(file, 0);
+			if (error && path)
+				error = git_mbedtls__set_cert_location(path, 1);
+		}
 #else
 		giterr_set(GITERR_SSL, "TLS backend doesn't support certificate locations");
 		error = -1;
@@ -199,7 +213,7 @@ int git_libgit2_opts(int key, ...)
 		break;
 
 	case GIT_OPT_SET_SSL_CIPHERS:
-#ifdef GIT_OPENSSL
+#if (GIT_OPENSSL || GIT_MBEDTLS)
 		{
 			git__free(git__ssl_ciphers);
 			git__ssl_ciphers = git__strdup(va_arg(ap, const char *));

src/streams/mbedtls.c

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "streams/mbedtls.h"
+
+#ifdef GIT_MBEDTLS
+
+#include <ctype.h>
+
+#include "global.h"
+#include "stream.h"
+#include "streams/socket.h"
+#include "netops.h"
+#include "git2/transport.h"
+#include "util.h"
+
+#ifdef GIT_CURL
+# include "streams/curl.h"
+#endif
+
+#ifndef GIT_DEFAULT_CERT_LOCATION
+#define GIT_DEFAULT_CERT_LOCATION NULL
+#endif
+
+#include <mbedtls/config.h>
+#include <mbedtls/ssl.h>
+#include <mbedtls/error.h>
+#include <mbedtls/entropy.h>
+#include <mbedtls/ctr_drbg.h>
+
+mbedtls_ssl_config *git__ssl_conf;
+mbedtls_entropy_context *mbedtls_entropy;
+
+#define GIT_SSL_DEFAULT_CIPHERS "TLS-ECDHE-ECDSA-WITH-AES-128-GCM-SHA256:TLS-ECDHE-RSA-WITH-AES-128-GCM-SHA256:TLS-ECDHE-ECDSA-WITH-AES-256-GCM-SHA384:TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384:TLS-DHE-RSA-WITH-AES-128-GCM-SHA256:TLS-DHE-DSS-WITH-AES-128-GCM-SHA256:TLS-DHE-RSA-WITH-AES-256-GCM-SHA384:TLS-DHE-DSS-WITH-AES-256-GCM-SHA384:TLS-ECDHE-ECDSA-WITH-AES-128-CBC-SHA256:TLS-ECDHE-RSA-WITH-AES-128-CBC-SHA256:TLS-ECDHE-ECDSA-WITH-AES-128-CBC-SHA:TLS-ECDHE-RSA-WITH-AES-128-CBC-SHA:TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA384:TLS-ECDHE-RSA-WITH-AES-256-CBC-SHA384:TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA:TLS-ECDHE-RSA-WITH-AES-256-CBC-SHA:TLS-DHE-RSA-WITH-AES-128-CBC-SHA256:TLS-DHE-RSA-WITH-AES-256-CBC-SHA256:TLS-DHE-RSA-WITH-AES-128-CBC-SHA:TLS-DHE-RSA-WITH-AES-256-CBC-SHA:TLS-DHE-DSS-WITH-AES-128-CBC-SHA256:TLS-DHE-DSS-WITH-AES-256-CBC-SHA256:TLS-DHE-DSS-WITH-AES-128-CBC-SHA:TLS-DHE-DSS-WITH-AES-256-CBC-SHA:TLS-RSA-WITH-AES-128-GCM-SHA256:TLS-RSA-WITH-AES-256-GCM-SHA384:TLS-RSA-WITH-AES-128-CBC-SHA256:TLS-RSA-WITH-AES-256-CBC-SHA256:TLS-RSA-WITH-AES-128-CBC-SHA:TLS-RSA-WITH-AES-256-CBC-SHA"
+#define GIT_SSL_DEFAULT_CIPHERS_COUNT 30
+
+/**
+ * This function aims to clean-up the SSL context which
+ * we allocated.
+ */
+static void shutdown_ssl(void)
+{
+	if (git__ssl_conf) {
+		mbedtls_x509_crt_free(git__ssl_conf->ca_chain);
+		git__free(git__ssl_conf->ca_chain);
+		mbedtls_ctr_drbg_free(git__ssl_conf->p_rng);
+		git__free(git__ssl_conf->p_rng);
+		mbedtls_ssl_config_free(git__ssl_conf);
+		git__free(git__ssl_conf);
+		git__ssl_conf = NULL;
+	}
+	if (mbedtls_entropy) {
+		mbedtls_entropy_free(mbedtls_entropy);
+		git__free(mbedtls_entropy);
+		mbedtls_entropy = NULL;
+	}
+}
+
+int git_mbedtls__set_cert_location(const char *path, int is_dir);
+
+int git_mbedtls_stream_global_init(void)
+{
+	int loaded = 0;
+	char *crtpath = GIT_DEFAULT_CERT_LOCATION;
+	struct stat statbuf;
+	mbedtls_ctr_drbg_context *ctr_drbg = NULL;
+
+	int *ciphers_list = NULL;
+	int ciphers_known = 0;
+	char *cipher_name = NULL;
+	char *cipher_string = NULL;
+	char *cipher_string_tmp = NULL;
+
+	mbedtls_x509_crt *cacert = NULL;
+
+	git__ssl_conf = git__malloc(sizeof(mbedtls_ssl_config));
+	mbedtls_ssl_config_init(git__ssl_conf);
+	if (mbedtls_ssl_config_defaults(git__ssl_conf,
+		                            MBEDTLS_SSL_IS_CLIENT,
+		                            MBEDTLS_SSL_TRANSPORT_STREAM,
+		                            MBEDTLS_SSL_PRESET_DEFAULT) != 0) {
+		giterr_set(GITERR_SSL, "failed to initialize mbedTLS");
+		goto cleanup;
+	}
+
+	/* configure TLSv1 */
+	mbedtls_ssl_conf_min_version(git__ssl_conf, MBEDTLS_SSL_MAJOR_VERSION_3, MBEDTLS_SSL_MINOR_VERSION_0);
+
+	/* verify_server_cert is responsible for making the check.
+	 * OPTIONAL because REQUIRED drops the certificate as soon as the check
+	 * is made, so we can never see the certificate and override it. */
+	mbedtls_ssl_conf_authmode(git__ssl_conf, MBEDTLS_SSL_VERIFY_OPTIONAL);
+
+	/* set the list of allowed ciphersuites */
+	ciphers_list = calloc(GIT_SSL_DEFAULT_CIPHERS_COUNT, sizeof(int));
+	ciphers_known = 0;
+	cipher_string = cipher_string_tmp = git__strdup(GIT_SSL_DEFAULT_CIPHERS);
+	while ((cipher_name = git__strtok(&cipher_string_tmp, ":")) != NULL) {
+		int cipherid = mbedtls_ssl_get_ciphersuite_id(cipher_name);
+		if (cipherid == 0) continue;
+
+		ciphers_list[ciphers_known++] = cipherid;
+	}
+	git__free(cipher_string);
+
+	if (!ciphers_known) {
+		giterr_set(GITERR_SSL, "no cipher could be enabled");
+		goto cleanup;
+	}
+	mbedtls_ssl_conf_ciphersuites(git__ssl_conf, ciphers_list);
+
+	/* Seeding the random number generator */
+	mbedtls_entropy = git__malloc(sizeof(mbedtls_entropy_context));
+	mbedtls_entropy_init(mbedtls_entropy);
+
+	ctr_drbg = git__malloc(sizeof(mbedtls_ctr_drbg_context));
+	mbedtls_ctr_drbg_init(ctr_drbg);
+	if (mbedtls_ctr_drbg_seed(ctr_drbg,
+		                      mbedtls_entropy_func,
+		                      mbedtls_entropy, NULL, 0) != 0) {
+		giterr_set(GITERR_SSL, "failed to initialize mbedTLS entropy pool");
+		goto cleanup;
+	}
+
+	mbedtls_ssl_conf_rng(git__ssl_conf, mbedtls_ctr_drbg_random, ctr_drbg);
+
+	/* load default certificates */
+	if (crtpath != NULL && stat(crtpath, &statbuf) == 0 && S_ISREG(statbuf.st_mode))
+		loaded = (git_mbedtls__set_cert_location(crtpath, 0) == 0);
+	if (!loaded && crtpath != NULL && stat(crtpath, &statbuf) == 0 && S_ISDIR(statbuf.st_mode))
+		loaded = (git_mbedtls__set_cert_location(crtpath, 1) == 0);
+
+	git__on_shutdown(shutdown_ssl);
+
+	return 0;
+
+cleanup:
+	mbedtls_x509_crt_free(cacert);
+	git__free(cacert);
+	mbedtls_ctr_drbg_free(ctr_drbg);
+	git__free(ctr_drbg);
+	mbedtls_ssl_config_free(git__ssl_conf);
+	git__free(git__ssl_conf);
+	git__ssl_conf = NULL;
+
+	return -1;
+}
+
+mbedtls_ssl_config *git__ssl_conf;
+
+static int bio_read(void *b, unsigned char *buf, size_t len)
+{
+	git_stream *io = (git_stream *) b;
+	return (int) git_stream_read(io, buf, len);
+}
+
+static int bio_write(void *b, const unsigned char *buf, size_t len)
+{
+	git_stream *io = (git_stream *) b;
+	return (int) git_stream_write(io, (const char *)buf, len, 0);
+}
+
+static int ssl_set_error(mbedtls_ssl_context *ssl, int error)
+{
+	char errbuf[512];
+	int ret = -1;
+
+	assert(error != MBEDTLS_ERR_SSL_WANT_READ);
+	assert(error != MBEDTLS_ERR_SSL_WANT_WRITE);
+
+	if (error != 0)
+		mbedtls_strerror( error, errbuf, 512 );
+
+	switch(error) {
+		case 0:
+		giterr_set(GITERR_SSL, "SSL error: unknown error");
+		break;
+
+	case MBEDTLS_ERR_X509_CERT_VERIFY_FAILED:
+		giterr_set(GITERR_SSL, "SSL error: %#04x [%x] - %s", error, ssl->session_negotiate->verify_result, errbuf);
+		ret = GIT_ECERTIFICATE;
+		break;
+
+	default:
+		giterr_set(GITERR_SSL, "SSL error: %#04x - %s", error, errbuf);
+	}
+
+	return ret;
+}
+
+static int ssl_teardown(mbedtls_ssl_context *ssl)
+{
+	int ret = 0;
+
+	ret = mbedtls_ssl_close_notify(ssl);
+	if (ret < 0)
+		ret = ssl_set_error(ssl, ret);
+
+	mbedtls_ssl_free(ssl);
+	return ret;
+}
+
+static int verify_server_cert(mbedtls_ssl_context *ssl)
+{
+	int ret = -1;
+
+	if ((ret = mbedtls_ssl_get_verify_result(ssl)) != 0) {
+		char vrfy_buf[512];
+		int len = mbedtls_x509_crt_verify_info(vrfy_buf, sizeof(vrfy_buf), "", ret);
+		if (len >= 1) vrfy_buf[len - 1] = '\0'; /* Remove trailing \n */
+		giterr_set(GITERR_SSL, "the SSL certificate is invalid: %#04x - %s", ret, vrfy_buf);
+		return GIT_ECERTIFICATE;
+	}
+
+	return 0;
+}
+
+typedef struct {
+	git_stream parent;
+	git_stream *io;
+	bool connected;
+	char *host;
+	mbedtls_ssl_context *ssl;
+	git_cert_x509 cert_info;
+} mbedtls_stream;
+
+
+int mbedtls_connect(git_stream *stream)
+{
+	int ret;
+	mbedtls_stream *st = (mbedtls_stream *) stream;
+
+	if ((ret = git_stream_connect(st->io)) < 0)
+		return ret;
+
+	st->connected = true;
+
+	mbedtls_ssl_set_hostname(st->ssl, st->host);
+
+	mbedtls_ssl_set_bio(st->ssl, st->io, bio_write, bio_read, NULL);
+
+	if ((ret = mbedtls_ssl_handshake(st->ssl)) != 0)
+		return ssl_set_error(st->ssl, ret);
+
+	return verify_server_cert(st->ssl);
+}
+
+int mbedtls_certificate(git_cert **out, git_stream *stream)
+{
+	unsigned char *encoded_cert;
+	mbedtls_stream *st = (mbedtls_stream *) stream;
+
+	const mbedtls_x509_crt *cert = mbedtls_ssl_get_peer_cert(st->ssl);
+	if (!cert) {
+		giterr_set(GITERR_SSL, "the server did not provide a certificate");
+		return -1;
+	}
+
+	/* Retrieve the length of the certificate first */
+	if (cert->raw.len == 0) {
+		giterr_set(GITERR_NET, "failed to retrieve certificate information");
+		return -1;
+	}
+
+	encoded_cert = git__malloc(cert->raw.len);
+	GITERR_CHECK_ALLOC(encoded_cert);
+	memcpy(encoded_cert, cert->raw.p, cert->raw.len);
+
+	st->cert_info.parent.cert_type = GIT_CERT_X509;
+	st->cert_info.data = encoded_cert;
+	st->cert_info.len = cert->raw.len;
+
+	*out = &st->cert_info.parent;
+
+	return 0;
+}
+
+static int mbedtls_set_proxy(git_stream *stream, const git_proxy_options *proxy_options)
+{
+	mbedtls_stream *st = (mbedtls_stream *) stream;
+
+	return git_stream_set_proxy(st->io, proxy_options);
+}
+
+ssize_t mbedtls_stream_write(git_stream *stream, const char *data, size_t len, int flags)
+{
+	size_t read = 0;
+	mbedtls_stream *st = (mbedtls_stream *) stream;
+
+	GIT_UNUSED(flags);
+
+	do {
+		int error = mbedtls_ssl_write(st->ssl, (const unsigned char *)data + read, len - read);
+		if (error <= 0) {
+			return ssl_set_error(st->ssl, error);
+		}
+		read += error;
+	} while (read < len);
+
+	return read;
+}
+
+ssize_t mbedtls_stream_read(git_stream *stream, void *data, size_t len)
+{
+	mbedtls_stream *st = (mbedtls_stream *) stream;
+	int ret;
+
+	if ((ret = mbedtls_ssl_read(st->ssl, (unsigned char *)data, len)) <= 0)
+		ssl_set_error(st->ssl, ret);
+
+	return ret;
+}
+
+int mbedtls_stream_close(git_stream *stream)
+{
+	mbedtls_stream *st = (mbedtls_stream *) stream;
+	int ret = 0;
+
+	if (st->connected && (ret = ssl_teardown(st->ssl)) != 0)
+		return -1;
+
+	st->connected = false;
+
+	return git_stream_close(st->io);
+}
+
+void mbedtls_stream_free(git_stream *stream)
+{
+	mbedtls_stream *st = (mbedtls_stream *) stream;
+
+	git__free(st->host);
+	git__free(st->cert_info.data);
+	git_stream_free(st->io);
+	git__free(st->ssl);
+	git__free(st);
+}
+
+int git_mbedtls_stream_new(git_stream **out, const char *host, const char *port)
+{
+	int error;
+	mbedtls_stream *st;
+
+	st = git__calloc(1, sizeof(mbedtls_stream));
+	GITERR_CHECK_ALLOC(st);
+
+#ifdef GIT_CURL
+	error = git_curl_stream_new(&st->io, host, port);
+#else
+	error = git_socket_stream_new(&st->io, host, port);
+#endif
+
+	if (error < 0)
+		goto out_err;
+
+	st->ssl = git__malloc(sizeof(mbedtls_ssl_context));
+	GITERR_CHECK_ALLOC(st->ssl);
+	mbedtls_ssl_init(st->ssl);
+	if (mbedtls_ssl_setup(st->ssl, git__ssl_conf)) {
+		giterr_set(GITERR_SSL, "failed to create ssl object");
+		error = -1;
+		goto out_err;
+	}
+
+	st->host = git__strdup(host);
+	GITERR_CHECK_ALLOC(st->host);
+
+	st->parent.version = GIT_STREAM_VERSION;
+	st->parent.encrypted = 1;
+	st->parent.proxy_support = git_stream_supports_proxy(st->io);
+	st->parent.connect = mbedtls_connect;
+	st->parent.certificate = mbedtls_certificate;
+	st->parent.set_proxy = mbedtls_set_proxy;
+	st->parent.read = mbedtls_stream_read;
+	st->parent.write = mbedtls_stream_write;
+	st->parent.close = mbedtls_stream_close;
+	st->parent.free = mbedtls_stream_free;
+
+	*out = (git_stream *) st;
+	return 0;
+
+out_err:
+	mbedtls_ssl_free(st->ssl);
+	git_stream_free(st->io);
+	git__free(st);
+
+	return error;
+}
+
+int git_mbedtls__set_cert_location(const char *path, int is_dir)
+{
+	int ret = 0;
+	char errbuf[512];
+	mbedtls_x509_crt *cacert;
+
+	assert(path != NULL);
+
+	cacert = git__malloc(sizeof(mbedtls_x509_crt));
+	mbedtls_x509_crt_init(cacert);
+	if (is_dir) {
+		ret = mbedtls_x509_crt_parse_path(cacert, path);
+	} else {
+		ret = mbedtls_x509_crt_parse_file(cacert, path);
+	}
+	/* mbedtls_x509_crt_parse_path returns the number of invalid certs on success */
+	if (ret < 0) {
+		mbedtls_x509_crt_free(cacert);
+		git__free(cacert);
+		mbedtls_strerror( ret, errbuf, 512 );
+		giterr_set(GITERR_SSL, "failed to load CA certificates: %#04x - %s", ret, errbuf);
+		return -1;
+	}
+
+	mbedtls_x509_crt_free(git__ssl_conf->ca_chain);
+	git__free(git__ssl_conf->ca_chain);
+	mbedtls_ssl_conf_ca_chain(git__ssl_conf, cacert, NULL);
+
+	return 0;
+}
+
+#else
+
+#include "stream.h"
+
+int git_mbedtls_stream_global_init(void)
+{
+	return 0;
+}
+
+int git_mbedtls_stream_new(git_stream **out, const char *host, const char *port)
+{
+	GIT_UNUSED(out);
+	GIT_UNUSED(host);
+	GIT_UNUSED(port);
+
+	giterr_set(GITERR_SSL, "mbedTLS is not supported in this version");
+	return -1;
+}
+
+int git_mbedtls__set_cert_location(const char *path, int is_dir)
+{
+	GIT_UNUSED(path);
+	GIT_UNUSED(is_dir);
+
+	giterr_set(GITERR_SSL, "mbedTLS is not supported in this version");
+	return -1;
+}
+
+#endif

src/streams/mbedtls.h

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_steams_mbedtls_h__
+#define INCLUDE_steams_mbedtls_h__
+
+#include "common.h"
+
+#include "git2/sys/stream.h"
+
+extern int git_mbedtls_stream_global_init(void);
+
+extern int git_mbedtls_stream_new(git_stream **out, const char *host, const char *port);
+
+extern int git_mbedtls__set_cert_location(const char *path, int is_dir);
+
+#endif

src/streams/tls.c

@@ -9,6 +9,7 @@
 
 #include "git2/errors.h"
 
+#include "streams/mbedtls.h"
 #include "streams/openssl.h"
 #include "streams/stransport.h"
 
@@ -31,6 +32,8 @@ int git_tls_stream_new(git_stream **out, const char *host, const char *port)
 	return git_stransport_stream_new(out, host, port);
 #elif defined(GIT_OPENSSL)
 	return git_openssl_stream_new(out, host, port);
+#elif defined(GIT_MBEDTLS)
+	return git_mbedtls_stream_new(out, host, port);
 #else
 	GIT_UNUSED(out);
 	GIT_UNUSED(host);

tests/core/stream.c

@@ -33,9 +33,8 @@ void test_core_stream__register_tls(void)
 	cl_git_pass(git_stream_register_tls(NULL));
 	error = git_tls_stream_new(&stream, "localhost", "443");
 
-	/* We don't have arbitrary TLS stream support on Windows
-	 * or when openssl support is disabled (except on OSX
-	 * with Security framework).
+	/* We don't have TLS support enabled, or we're on Windows,
+	 * which has no arbitrary TLS stream support.
 	 */
 #if defined(GIT_WIN32) || !defined(GIT_HTTPS)
 	cl_git_fail_with(-1, error);