dhcp: put option 53 at the beginning2023_10_04.f851084

... unless it is listed in 55.
Many clients expect option 53 at the beginning.
mTCP has this code:
  if ( resp->options[0] != 53 ) {
    TRACE_WARN(( "Dhcp: first option was not a Dhcp msg type\n" ));
    return;
  }

wattcp32 has this:
static int DHCP_is_ack (void)
{
  const BYTE *opt = (const BYTE*) &dhcp_in.dh_opt[4];

  return (opt[0] == DHCP_OPT_MSG_TYPE && opt[1] == 1 && opt[2] == DHCP_ACK);
}
static int DHCP_is_nack (void)
{
  const BYTE *opt = (const BYTE*) &dhcp_in.dh_opt[4];

  return (opt[0] == DHCP_OPT_MSG_TYPE && opt[1] == 1 && opt[2] == DHCP_NAK);
}

Link: https://bugs.passt.top/show_bug.cgi?id=77
Signed-off-by: Stas Sergeev <stsp2@yandex.ru>
[sbrivio: s/options 53/option 53/ and s/other/others/ in comment]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/dhcp.c b/dhcp.c
index 46c258e..53b4029 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -149,6 +149,13 @@ static int fill(struct msg *m)
 	for (o = 0; o < 255; o++)
 		opts[o].sent = 0;
 
+	/* Some clients (wattcp32, mTCP, maybe some others) expect
+	 * option 53 at the beginning of the list.
+	 * Put it there explicitly, unless requested via option 55.
+	 */
+	if (!memchr(opts[55].c, 53, opts[55].clen))
+		fill_one(m, 53, &offset);
+
 	for (i = 0; i < opts[55].clen; i++) {
 		o = opts[55].c[i];
 		if (opts[o].slen)