udhcp: make arpping code resistant to time jumps

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/networking/udhcp/arpping.c b/networking/udhcp/arpping.c
index ff63478..b43e52e 100644 (file)
--- a/networking/udhcp/arpping.c
+++ b/networking/udhcp/arpping.c
@@ -118,8 +118,13 @@ int FAST_FUNC arpping(uint32_t test_nip,
                                break;
                        }
                }
-               timeout_ms -= (unsigned)monotonic_ms() - prevTime;
-       } while (timeout_ms > 0);
+               timeout_ms -= (unsigned)monotonic_ms() - prevTime + 1;
+
+               /* We used to check "timeout_ms > 0", but
+                * this is more under/overflow-resistant
+                * (people did see overflows here when system time jumps):
+                */
+       } while ((unsigned)timeout_ms <= 2000);
 
  ret:
        close(s);