commit d0b24860363a3704e28569ce9a6987717834edea
Author: Miroslav Lichvar <mlichvar@redhat.com>
Date:   Tue Dec 5 11:08:24 2017 +0100

    client: don't call select() with invalid timeout
    
    If the system clock was stepped forward after chronyc sent a request and
    before it read the clock in order to calculate the receive timeout,
    select() could be called with a negative timeout, which resulted in an
    infinite loop waiting for select() to succeed.
    
    Fix the submit_request() function to not call select() with a negative
    timeout. Also, return immediately on any error of select().

diff --git a/client.c b/client.c
index 5c3a99e..4e23158 100644
--- a/client.c
+++ b/client.c
@@ -1394,9 +1394,16 @@ submit_request(CMD_Request *request, CMD_Reply *reply)
 
     timeout = initial_timeout / 1000.0 * (1U << (n_attempts - 1)) -
               UTI_DiffTimespecsToDouble(&ts_now, &ts_start);
-    UTI_DoubleToTimeval(timeout, &tv);
     DEBUG_LOG("Timeout %f seconds", timeout);
 
+    /* Avoid calling select() with an invalid timeout */
+    if (timeout <= 0.0) {
+      new_attempt = 1;
+      continue;
+    }
+
+    UTI_DoubleToTimeval(timeout, &tv);
+
     FD_ZERO(&rdfd);
     FD_ZERO(&wrfd);
     FD_ZERO(&exfd);
@@ -1410,6 +1417,7 @@ submit_request(CMD_Request *request, CMD_Reply *reply)
 
     if (select_status < 0) {
       DEBUG_LOG("select failed : %s", strerror(errno));
+      return 0;
     } else if (select_status == 0) {
       /* Timeout must have elapsed, try a resend? */
       new_attempt = 1;