dhcpd: fix an improper widening conversion

We wanted to detect when tv_sec = unsigned1 - unsigned2
underflows by looking at tv_sec's sign. But if tv_sec
is long and it is wider than unsigned, we get unsigned -> long
conversion which is in this case never negative.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/networking/udhcp/dhcpd.c b/networking/udhcp/dhcpd.c
index 4b3ed240c..2de074f9b 100644
--- a/networking/udhcp/dhcpd.c
+++ b/networking/udhcp/dhcpd.c
@@ -413,7 +413,8 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
 
                 max_sock = udhcp_sp_fd_set(&rfds, server_socket);
                 if (server_config.auto_time) {
-                        tv.tv_sec = timeout_end - monotonic_sec();
+                        /* cast to signed is essential if tv_sec is wider than int */
+                        tv.tv_sec = (int)(timeout_end - monotonic_sec());
                         tv.tv_usec = 0;
                 }
                 retval = 0;