streams: openssl: switch approach to silence Valgrind errors

As OpenSSL loves using uninitialized bytes as another source of entropy,
we need to mark them as defined so that Valgrind won't complain about
use of these bytes. Traditionally, we've been using the macro
`VALGRIND_MAKE_MEM_DEFINED` provided by Valgrind, but starting with
OpenSSL 1.1 the code doesn't compile anymore due to `struct SSL` having
become opaque. As such, we also can't set it as defined anymore, as we
have no way of knowing its size.

Let's change gears instead by just swapping out the allocator functions
of OpenSSL with our own ones. The twist is that instead of calling
`malloc`, we just call `calloc` to have the bytes initialized
automatically. Next to soothing Valgrind, this approach has the benefit
of being completely agnostic of the memory sanitizer and is neatly
contained at a single place.

Note that we shouldn't do this for non-Valgrind builds. As we cannot
set up memory functions for a given SSL context, only, we need to swap
them at a global context. Furthermore, as it's possible to call
`OPENSSL_set_mem_functions` once only, we'd prevent users of libgit2 to
set up their own allocators.

src/streams/openssl.c

@@ -30,10 +30,6 @@
 #include <openssl/x509v3.h>
 #include <openssl/bio.h>
 
-#ifdef VALGRIND
-# include <valgrind/memcheck.h>
-#endif
-
 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"
@@ -200,16 +196,69 @@ static void shutdown_ssl(void)
 	}
 }
 
+#ifdef VALGRIND
+#ifdef OPENSSL_LEGACY_API
+static void *git_openssl_malloc(size_t bytes)
+{
+	return git__calloc(1, bytes);
+}
+
+static void *git_openssl_realloc(void *mem, size_t size)
+{
+	return git__realloc(mem, size);
+}
+
+static void git_openssl_free(void *mem)
+{
+	return git__free(mem);
+}
+#else
+static void *git_openssl_malloc(size_t bytes, const char *file, int line)
+{
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+	return git__calloc(1, bytes);
+}
+
+static void *git_openssl_realloc(void *mem, size_t size, const char *file, int line)
+{
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+	return git__realloc(mem, size);
+}
+
+static void git_openssl_free(void *mem, const char *file, int line)
+{
+	GIT_UNUSED(file);
+	GIT_UNUSED(line);
+	return git__free(mem);
+}
+#endif
+#endif
+
 int git_openssl_stream_global_init(void)
 {
 	long ssl_opts = SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3;
 	const char *ciphers = git_libgit2__ssl_ciphers();
+#ifdef VALGRIND
+	static bool allocators_initialized = false;
+#endif
 
 	/* Older OpenSSL and MacOS OpenSSL doesn't have this */
 #ifdef SSL_OP_NO_COMPRESSION
 	ssl_opts |= SSL_OP_NO_COMPRESSION;
 #endif
 
+#ifdef VALGRIND
+	/* Swap in our own allocator functions that initialize allocated memory */
+	if (!allocators_initialized &&
+	    CRYPTO_set_mem_functions(git_openssl_malloc,
+				     git_openssl_realloc,
+				     git_openssl_free) != 1)
+		goto error;
+	allocators_initialized = true;
+#endif
+
 	OPENSSL_init_ssl(0, NULL);
 
 	/*
@@ -314,11 +363,6 @@ static int bio_read(BIO *b, char *buf, int len)
 static int bio_write(BIO *b, const char *buf, int len)
 {
 	git_stream *io = (git_stream *) BIO_get_data(b);
-
-#ifdef VALGRIND
-	VALGRIND_MAKE_MEM_DEFINED(buf, len);
-#endif
-
 	return (int) git_stream_write(io, buf, len, 0);
 }
 
@@ -595,10 +639,6 @@ static int openssl_connect(git_stream *stream)
 	BIO_set_data(bio, st->io);
 	SSL_set_bio(st->ssl, bio, bio);
 
-#ifdef VALGRIND
-	VALGRIND_MAKE_MEM_DEFINED(st->ssl, sizeof(SSL));
-#endif
-
 	/* specify the host in case SNI is needed */
 #ifdef SSL_CTRL_SET_TLSEXT_HOSTNAME
 	SSL_set_tlsext_host_name(st->ssl, st->host);
@@ -609,10 +649,6 @@ static int openssl_connect(git_stream *stream)
 
 	st->connected = true;
 
-#ifdef VALGRIND
-	VALGRIND_MAKE_MEM_DEFINED(st->ssl, sizeof(SSL));
-#endif
-
 	return verify_server_cert(st->ssl, st->host);
 }
 
@@ -679,10 +715,6 @@ static ssize_t openssl_read(git_stream *stream, void *data, size_t len)
 	if ((ret = SSL_read(st->ssl, data, len)) <= 0)
 		return ssl_set_error(st->ssl, ret);
 
-#ifdef VALGRIND
-	VALGRIND_MAKE_MEM_DEFINED(data, ret);
-#endif
-
 	return ret;
 }