Treat zero timeout as infinite

The other possible behavior (instantly failing the service call) is not
useful.

Fixes: QubesOS/qubes-issues#9126
Fixes: c664954 ("Avoid using alarm(2) for timeouts")

Author: DemiMarie

libqrexec/vchan_timeout.c

@@ -16,25 +16,27 @@ int qubes_wait_for_vchan_connection_with_timeout(
     assert(end_tp.tv_nsec >= 0 && end_tp.tv_nsec < BILLION_NANOSECONDS);
     end_tp.tv_sec += timeout;
     for (;;) {
-        bool did_timeout = true;
         struct pollfd fds = { .fd = wait_fd, .events = POLLIN | POLLHUP, .revents = 0 };
+        bool did_timeout = timeout > 0;
 
         /* calculate how much time left until connection timeout expire */
-        if (clock_gettime(CLOCK_MONOTONIC, &now_tp)) {
-            PERROR("clock_gettime");
-            return -1;
-        }
-        assert(now_tp.tv_nsec >= 0 && now_tp.tv_nsec < BILLION_NANOSECONDS);
-        if (now_tp.tv_sec <= end_tp.tv_sec) {
-            timeout_tp.tv_sec = end_tp.tv_sec - now_tp.tv_sec;
-            timeout_tp.tv_nsec = end_tp.tv_nsec - now_tp.tv_nsec;
-            if (timeout_tp.tv_nsec < 0) {
-                timeout_tp.tv_nsec += BILLION_NANOSECONDS;
-                timeout_tp.tv_sec--;
+        if (did_timeout) {
+            if (clock_gettime(CLOCK_MONOTONIC, &now_tp)) {
+                PERROR("clock_gettime");
+                return -1;
+            }
+            assert(now_tp.tv_nsec >= 0 && now_tp.tv_nsec < BILLION_NANOSECONDS);
+            if (now_tp.tv_sec <= end_tp.tv_sec) {
+                timeout_tp.tv_sec = end_tp.tv_sec - now_tp.tv_sec;
+                timeout_tp.tv_nsec = end_tp.tv_nsec - now_tp.tv_nsec;
+                if (timeout_tp.tv_nsec < 0) {
+                    timeout_tp.tv_nsec += BILLION_NANOSECONDS;
+                    timeout_tp.tv_sec--;
+                }
+                did_timeout = timeout_tp.tv_sec < 0;
             }
-            did_timeout = timeout_tp.tv_sec < 0;
         }
-        switch (did_timeout ? 0 : ppoll(&fds, 1, &timeout_tp, NULL)) {
+        switch (did_timeout ? 0 : ppoll(&fds, 1, timeout > 0 ? &timeout_tp : NULL, NULL)) {
             case -1:
                 if (errno == EINTR)
                     break;

qrexec/tests/socket/daemon.py

@@ -734,7 +734,7 @@ def test_run_vm_command_and_connect_vm(self):
         self.client.wait()
         self.assertEqual(self.client.returncode, 0)
 
-    def connect_service_request(self, cmd):
+    def connect_service_request(self, cmd, timeout=None):
         request_id = "SOCKET11"
         src_domain_name = "src_domain"
         src_domain = 43
@@ -749,6 +749,7 @@ def connect_service_request(self, cmd):
                 "dom0",
                 "-c",
                 "{},{},{}".format(request_id, src_domain_name, src_domain),
+                *([f"-w{timeout}"] if timeout is not None else []),
                 cmd,
             ]
         )
@@ -1010,7 +1011,7 @@ def test_run_dom0_service_socket_shutdown_rd(self):
         server = qrexec.socket_server(socket_path)
         self.addCleanup(server.close)
         cmd = "QUBESRPC qubes.SocketService+arg src_domain name src_domain"
-        source = self.connect_service_request(cmd)
+        source = self.connect_service_request(cmd, timeout=0)
 
         server.accept()
         header = cmd[len("QUBESRPC ") :].encode() + b"\0"