in DTLS don't use writev() when multiple packets which exceed MTU are queued

That change requires the system_write() to be registered unconditionally,
even when writev() is available.
Resolves: https://savannah.gnu.org/support/?108715

4 files changed, 27 insertions, 12 deletions

diff --git a/lib/gnutls_buffers.c b/lib/gnutls_buffers.c
index 24e52b1b96..ef2ad236b3 100644
--- a/lib/gnutls_buffers.c
+++ b/lib/gnutls_buffers.c
@@ -460,14 +460,30 @@ _gnutls_writev_emu(gnutls_session_t session, gnutls_transport_ptr_t fd,
 
 static ssize_t
 _gnutls_writev(gnutls_session_t session, const giovec_t * giovec,
-	       int giovec_cnt)
+	       unsigned giovec_cnt)
 {
 	int i;
+	bool is_dtls = IS_DTLS(session);
+	bool no_writev = 0;
 	gnutls_transport_ptr_t fd = session->internals.transport_send_ptr;
 
 	reset_errno(session);
 
-	if (session->internals.push_func != NULL)
+	/* In DTLS we use writev() only when the total sum is less than
+	 * the MTU. */
+
+	if (is_dtls && giovec_cnt > 1) {
+		unsigned sum = 0, j;
+		for (j = 0; j < giovec_cnt; j++) {
+			sum += giovec[j].iov_len;
+		}
+
+		if (sum > session->internals.dtls.mtu) {
+			no_writev = 1;
+		}
+	}
+
+	if (session->internals.push_func != NULL || no_writev != 0)
 		i = _gnutls_writev_emu(session, fd, giovec, giovec_cnt);
 	else
 		i = session->internals.vec_push_func(fd, giovec,
@@ -477,7 +493,7 @@ _gnutls_writev(gnutls_session_t session, const giovec_t * giovec,
 		int err = get_errno(session);
 		_gnutls_debug_log("errno: %d\n", err);
 
-		return errno_to_gerr(err, IS_DTLS(session));
+		return errno_to_gerr(err, is_dtls);
 	}
 	return i;
 }
diff --git a/lib/gnutls_state.c b/lib/gnutls_state.c
index 623e9cfd5e..c964822bcb 100644
--- a/lib/gnutls_state.c
+++ b/lib/gnutls_state.c
@@ -376,9 +376,8 @@ int gnutls_init(gnutls_session_t * session, unsigned int flags)
 
 #ifdef HAVE_WRITEV
 	gnutls_transport_set_vec_push_function(*session, system_writev);
-#else
-	gnutls_transport_set_push_function(*session, system_write);
 #endif
+	gnutls_transport_set_push_function(*session, system_write);
 	(*session)->internals.pull_timeout_func = system_recv_timeout;
 	(*session)->internals.pull_func = system_read;
 	(*session)->internals.errno_func = system_errno;
diff --git a/lib/system.c b/lib/system.c
index d866e19aa3..9504cfe8c6 100644
--- a/lib/system.c
+++ b/lib/system.c
@@ -60,6 +60,12 @@ static HMODULE Crypt32_dll;
 /* System specific function wrappers.
  */
 
+ssize_t
+system_write(gnutls_transport_ptr ptr, const void *data, size_t data_size)
+{
+	return send(GNUTLS_POINTER_TO_INT(ptr), data, data_size, 0);
+}
+
 #ifdef _WIN32
 /* Do not use the gnulib functions for sending and receiving data.
  * Using them makes gnutls only working with gnulib applications.
@@ -94,11 +100,6 @@ int system_errno(gnutls_transport_ptr p)
 	return ret;
 }
 
-ssize_t
-system_write(gnutls_transport_ptr ptr, const void *data, size_t data_size)
-{
-	return send(GNUTLS_POINTER_TO_INT(ptr), data, data_size, 0);
-}
 #else				/* POSIX */
 int system_errno(gnutls_transport_ptr_t ptr)
 {
diff --git a/lib/system.h b/lib/system.h
index d94b1564ee..f9b067538c 100644
--- a/lib/system.h
+++ b/lib/system.h
@@ -42,10 +42,9 @@
 int system_errno(gnutls_transport_ptr_t);
 int system_recv_timeout(gnutls_transport_ptr_t ptr, unsigned int ms);
 
-#ifdef _WIN32
 ssize_t system_write(gnutls_transport_ptr_t ptr, const void *data,
 		     size_t data_size);
-#else
+#ifndef _WIN32
 #define HAVE_WRITEV
 ssize_t system_writev(gnutls_transport_ptr_t ptr, const giovec_t * iovec,
 		      int iovec_cnt);