1 files changed, 9 insertions, 0 deletions

diff --git a/networking/udhcp/packet.c b/networking/udhcp/packet.c
index 33c9585cf..148f52551 100644
--- a/networking/udhcp/packet.c
+++ b/networking/udhcp/packet.c
@@ -143,8 +143,15 @@ int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
          *
          * In order to work with those buggy servers,
          * we truncate packets after end option byte.
+         *
+         * However, RFC 1542 says "The IP Total Length and UDP Length
+         * must be large enough to contain the minimal BOOTP header of 300 octets".
+         * Thus, we retain enough padding to not go below 300 BOOTP bytes.
+         * Some devices have filters which drop DHCP packets shorter than that.
          */
         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
+        if (padding > DHCP_SIZE - 300)
+                padding = DHCP_SIZE - 300;
 
         packet.ip.protocol = IPPROTO_UDP;
         packet.ip.saddr = source_nip;
@@ -215,6 +222,8 @@ int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
 
         udhcp_dump_packet(dhcp_pkt);
         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
+        if (padding > DHCP_SIZE - 300)
+                padding = DHCP_SIZE - 300;
         result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
         msg = "write";
  ret_close: