- Patch from Vadim Fedorenko that adds MSG_DONTWAIT to receive

  operations, so that instruction reordering does not cause mistakenly
  blocking socket operations.

diff --git a/dnstap/dtstream.c b/dnstap/dtstream.c
index a1dd9703ea95e927dc3326be07369108d212b0ee..377ae9916db37c4f891f7c0785cbeff6758bff65 100644 (file)
--- a/dnstap/dtstream.c
+++ b/dnstap/dtstream.c
@@ -954,7 +954,7 @@ static int dtio_write_more(struct dt_io_thread* dtio)
  * -1: continue, >0: number of bytes read into buffer */
 static ssize_t receive_bytes(struct dt_io_thread* dtio, void* buf, size_t len) {
        ssize_t r;
-       r = recv(dtio->fd, (void*)buf, len, 0);
+       r = recv(dtio->fd, (void*)buf, len, MSG_DONTWAIT);
        if(r == -1) {
                char* to = dtio->socket_path;
                if(!to) to = dtio->ip_str;

diff --git a/dnstap/unbound-dnstap-socket.c b/dnstap/unbound-dnstap-socket.c
index 63292fbca36edbfa9a74efd7813c8f3067c0205a..1cc45027730aaa43f3fefaa59618b76b16bb6758 100644 (file)
--- a/dnstap/unbound-dnstap-socket.c
+++ b/dnstap/unbound-dnstap-socket.c
@@ -617,7 +617,7 @@ static void log_data_frame(uint8_t* pkt, size_t len)
 static ssize_t receive_bytes(struct tap_data* data, int fd, void* buf,
        size_t len)
 {
-       ssize_t ret = recv(fd, buf, len, 0);
+       ssize_t ret = recv(fd, buf, len, MSG_DONTWAIT);
        if(ret == 0) {
                /* closed */
                if(verbosity) log_info("dnstap client stream closed from %s",

diff --git a/doc/Changelog b/doc/Changelog
index ed3812c69cb4cb4d9429af74b1087bd5b47d1e7c..10d16e6ebec932595c18abfdc9059a389c251ea3 100644 (file)
--- a/doc/Changelog
+++ b/doc/Changelog
@@ -1,6 +1,9 @@
 31 August 2022: Wouter
        - Fix to avoid process wide fcntl calls mixed with nonblocking
          operations after a blocked write.
+       - Patch from Vadim Fedorenko that adds MSG_DONTWAIT to receive
+         operations, so that instruction reordering does not cause mistakenly
+         blocking socket operations.
 
 22 August 2022: Wouter
        - Fix #741: systemd socket activation fails on IPv6.

diff --git a/util/net_help.h b/util/net_help.h
index 4dd398460294474460c4446060b7b8dc117b594b..fc23b218189804e13b9fc770481ec006674dc3d8 100644 (file)
--- a/util/net_help.h
+++ b/util/net_help.h
@@ -96,6 +96,11 @@ extern uint16_t EDNS_ADVERTISED_SIZE;
 /** return a random 16-bit number given a random source */
 #define GET_RANDOM_ID(rnd) (((unsigned)ub_random(rnd)>>8) & 0xffff)
 
+/** define MSG_DONTWAIT for unsupported platforms */
+#ifndef MSG_DONTWAIT
+#define MSG_DONTWAIT 0
+#endif
+
 /** minimal responses when positive answer */
 extern int MINIMAL_RESPONSES;
 

diff --git a/util/netevent.c b/util/netevent.c
index 5bc8d8bcde3d9ff6604b6a5d3f4bcb489f9c56f3..6e2412f5a781da4523db8a7db68f6832a8baec39 100644 (file)
--- a/util/netevent.c
+++ b/util/netevent.c
@@ -701,7 +701,7 @@ comm_point_udp_ancil_callback(int fd, short event, void* arg)
                msg.msg_controllen = sizeof(ancil.buf);
 #endif /* S_SPLINT_S */
                msg.msg_flags = 0;
-               rcv = recvmsg(fd, &msg, 0);
+               rcv = recvmsg(fd, &msg, MSG_DONTWAIT);
                if(rcv == -1) {
                        if(errno != EAGAIN && errno != EINTR
                                && udp_recv_needs_log(errno)) {
@@ -781,7 +781,7 @@ comm_point_udp_callback(int fd, short event, void* arg)
                log_assert(fd != -1);
                log_assert(sldns_buffer_remaining(rep.c->buffer) > 0);
                rcv = recvfrom(fd, (void*)sldns_buffer_begin(rep.c->buffer), 
-                       sldns_buffer_remaining(rep.c->buffer), 0, 
+                       sldns_buffer_remaining(rep.c->buffer), MSG_DONTWAIT,
                        (struct sockaddr*)&rep.addr, &rep.addrlen);
                if(rcv == -1) {
 #ifndef USE_WINSOCK
@@ -1703,7 +1703,7 @@ comm_point_tcp_handle_read(int fd, struct comm_point* c, int short_ok)
        if(c->tcp_byte_count < sizeof(uint16_t)) {
                /* read length bytes */
                r = recv(fd,(void*)sldns_buffer_at(c->buffer,c->tcp_byte_count),
-                       sizeof(uint16_t)-c->tcp_byte_count, 0);
+                       sizeof(uint16_t)-c->tcp_byte_count, MSG_DONTWAIT);
                if(r == 0) {
                        if(c->tcp_req_info)
                                return tcp_req_info_handle_read_close(c->tcp_req_info);
@@ -1794,7 +1794,7 @@ comm_point_tcp_handle_read(int fd, struct comm_point* c, int short_ok)
        if(sldns_buffer_remaining(c->buffer) == 0)
                log_err("in comm_point_tcp_handle_read buffer_remaining is not > 0 as expected, continuing with (harmless) 0 length recv");
        r = recv(fd, (void*)sldns_buffer_current(c->buffer), 
-               sldns_buffer_remaining(c->buffer), 0);
+               sldns_buffer_remaining(c->buffer), MSG_DONTWAIT);
        if(r == 0) {
                if(c->tcp_req_info)
                        return tcp_req_info_handle_read_close(c->tcp_req_info);
@@ -2336,7 +2336,7 @@ http_read_more(int fd, struct comm_point* c)
        ssize_t r;
        log_assert(sldns_buffer_remaining(c->buffer) > 0);
        r = recv(fd, (void*)sldns_buffer_current(c->buffer), 
-               sldns_buffer_remaining(c->buffer), 0);
+               sldns_buffer_remaining(c->buffer), MSG_DONTWAIT);
        if(r == 0) {
                return 0;
        } else if(r == -1) {
@@ -2774,7 +2774,7 @@ ssize_t http2_recv_cb(nghttp2_session* ATTR_UNUSED(session), uint8_t* buf,
        }
 #endif /* HAVE_SSL */
 
-       ret = recv(h2_session->c->fd, buf, len, 0);
+       ret = recv(h2_session->c->fd, buf, len, MSG_DONTWAIT);
        if(ret == 0) {
                return NGHTTP2_ERR_EOF;
        } else if(ret < 0) {