From 2fa1c17cd9d1af515c2fa997726c9433d387f3f3 Mon Sep 17 00:00:00 2001
From: "W.C.A. Wijngaards" <wouter@nlnetlabs.nl>
Date: Wed, 31 Aug 2022 10:09:39 +0200
Subject: [PATCH] - Fix to avoid process wide fcntl calls mixed with
 nonblocking   operations after a blocked write.

---
 doc/Changelog   |  4 ++++
 util/netevent.c | 56 +++++++++++++++++++++++++++++++++----------------
 2 files changed, 42 insertions(+), 18 deletions(-)

diff --git a/doc/Changelog b/doc/Changelog
index 352516525..ed3812c69 100644
--- a/doc/Changelog
+++ b/doc/Changelog
@@ -1,3 +1,7 @@
+31 August 2022: Wouter
+	- Fix to avoid process wide fcntl calls mixed with nonblocking
+	  operations after a blocked write.
+
 22 August 2022: Wouter
 	- Fix #741: systemd socket activation fails on IPv6.
 
diff --git a/util/netevent.c b/util/netevent.c
index c2b1ac7d4..5bc8d8bcd 100644
--- a/util/netevent.c
+++ b/util/netevent.c
@@ -379,19 +379,30 @@ comm_point_send_udp_msg(struct comm_point *c, sldns_buffer* packet,
 			WSAGetLastError() == WSAENOBUFS ||
 			WSAGetLastError() == WSAEWOULDBLOCK) {
 #endif
-			int e;
-			fd_set_block(c->fd);
-			if (!is_connected) {
-				sent = sendto(c->fd, (void*)sldns_buffer_begin(packet),
-					sldns_buffer_remaining(packet), 0,
-					addr, addrlen);
-			} else {
-				sent = send(c->fd, (void*)sldns_buffer_begin(packet),
-					sldns_buffer_remaining(packet), 0);
+			/* if we set the fd blocking, other threads suddenly
+			 * have a blocking fd that they operate on */
+			while(
+#ifndef USE_WINSOCK
+				errno == EAGAIN ||
+#  ifdef EWOULDBLOCK
+				errno == EWOULDBLOCK ||
+#  endif
+				errno == ENOBUFS
+#else
+				WSAGetLastError() == WSAEINPROGRESS ||
+				WSAGetLastError() == WSAENOBUFS ||
+				WSAGetLastError() == WSAEWOULDBLOCK
+#endif
+			) {
+				if (!is_connected) {
+					sent = sendto(c->fd, (void*)sldns_buffer_begin(packet),
+						sldns_buffer_remaining(packet), 0,
+						addr, addrlen);
+				} else {
+					sent = send(c->fd, (void*)sldns_buffer_begin(packet),
+						sldns_buffer_remaining(packet), 0);
+				}
 			}
-			e = errno;
-			fd_set_nonblock(c->fd);
-			errno = e;
 		}
 	}
 	if(sent == -1) {
@@ -568,12 +579,21 @@ comm_point_send_udp_msg_if(struct comm_point *c, sldns_buffer* packet,
 			WSAGetLastError() == WSAENOBUFS ||
 			WSAGetLastError() == WSAEWOULDBLOCK) {
 #endif
-			int e;
-			fd_set_block(c->fd);
-			sent = sendmsg(c->fd, &msg, 0);
-			e = errno;
-			fd_set_nonblock(c->fd);
-			errno = e;
+			while(
+#ifndef USE_WINSOCK
+				errno == EAGAIN ||
+#  ifdef EWOULDBLOCK
+				errno == EWOULDBLOCK ||
+#  endif
+				errno == ENOBUFS
+#else
+				WSAGetLastError() == WSAEINPROGRESS ||
+				WSAGetLastError() == WSAENOBUFS ||
+				WSAGetLastError() == WSAEWOULDBLOCK
+#endif
+			) {
+				sent = sendmsg(c->fd, &msg, 0);
+			}
 		}
 	}
 	if(sent == -1) {
-- 
2.47.3