package/utils/busybox/patches/000-busybox-1.25.0-ntpd.patch

   1 ntpd: respond only to client and symmetric active packets
   2 The busybox NTP implementation doesn't check the NTP mode of packets
   3 received on the server port and responds to any packet with the right
   4 size. This includes responses from another NTP server. An attacker can
   5 send a packet with a spoofed source address in order to create an
   6 infinite loop of responses between two busybox NTP servers. Adding
   7 more packets to the loop increases the traffic between the servers
   8 until one of them has a fully loaded CPU and/or network.
   9
  10 Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
  11 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
  12
  13 --- a/networking/ntpd.c
  14 +++ b/networking/ntpd.c
  15 @@ -2051,6 +2051,13 @@ recv_and_process_client_pkt(void /*int f
  16                 goto bail;
  17         }
  18
  19 +       /* Respond only to client and symmetric active packets */
  20 +       if ((msg.m_status & MODE_MASK) != MODE_CLIENT
  21 +        && (msg.m_status & MODE_MASK) != MODE_SYM_ACT
  22 +       ) {
  23 +               goto bail;
  24 +       }
  25 +
  26         query_status = msg.m_status;
  27         query_xmttime = msg.m_xmttime;
  28