dhcp: Add option code byte in calculation for OPT_MAX boundary check

Otherwise we'll limit messages to 577 bytes, instead of 576 bytes as
intended:

  $ fqdn="thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.thirtytwocharactersforeachlabel.then_make_it_251_with_this"
  $ hostname="__eighteen_bytes__"
  $ ./pasta --fqdn ${fqdn} -H ${hostname} -p dhcp.pcap -- /sbin/dhclient -4
  Saving packet capture to dhcp.pcap
  $ tshark -r dhcp.pcap -V -Y 'dhcp.option.value == 5' | grep "Total Length"
      Total Length: 577

This was hidden by the issue fixed by commit bcc4908c2b4a ("dhcp
Remove option 255 length byte") until now.

Fixes: 31e8109a86ee ("dhcp, dhcpv6: Add hostname and client fqdn ops")
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Enrique Llorente <ellorent@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/dhcp.c b/dhcp.c
index 66a716e..b0de04b 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -143,7 +143,7 @@ static bool fill_one(struct msg *m, int o, int *offset)
 	size_t slen = opts[o].slen;
 
 	/* If we don't have space to write the option, then just skip */
-	if (*offset + 1 /* length of option */ + slen > OPT_MAX)
+	if (*offset + 2 /* code and length of option */ + slen > OPT_MAX)
 		return true;
 
 	m->o[*offset] = o;