63 lines
1.9 KiB
Go
63 lines
1.9 KiB
Go
|
package dns
|
||
|
|
|
||
|
|
// MsgAcceptFunc is used early in the server code to accept or reject a message with RcodeFormatError.
|
||
|
|
// It returns a MsgAcceptAction to indicate what should happen with the message.
|
||
|
|
type MsgAcceptFunc func(dh Header) MsgAcceptAction
|
||
|
|
|
||
|
|
// DefaultMsgAcceptFunc checks the request and will reject if:
|
||
|
|
//
|
||
|
|
// * isn't a request (don't respond in that case)
|
||
|
|
//
|
||
|
|
// * opcode isn't OpcodeQuery or OpcodeNotify
|
||
|
|
//
|
||
|
|
// * Zero bit isn't zero
|
||
|
|
//
|
||
|
|
// * does not have exactly 1 question in the question section
|
||
|
|
//
|
||
|
|
// * has more than 1 RR in the Answer section
|
||
|
|
//
|
||
|
|
// * has more than 0 RRs in the Authority section
|
||
|
|
//
|
||
|
|
// * has more than 2 RRs in the Additional section
|
||
|
|
//
|
||
|
|
var DefaultMsgAcceptFunc MsgAcceptFunc = defaultMsgAcceptFunc
|
||
|
|
|
||
|
|
// MsgAcceptAction represents the action to be taken.
|
||
|
|
type MsgAcceptAction int
|
||
|
|
|
||
|
|
// Allowed returned values from a MsgAcceptFunc.
|
||
|
|
const (
|
||
|
|
MsgAccept MsgAcceptAction = iota // Accept the message
|
||
|
|
MsgReject // Reject the message with a RcodeFormatError
|
||
|
|
MsgIgnore // Ignore the error and send nothing back.
|
||
|
|
MsgRejectNotImplemented // Reject the message with a RcodeNotImplemented
|
||
|
|
)
|
||
|
|
|
||
|
|
func defaultMsgAcceptFunc(dh Header) MsgAcceptAction {
|
||
|
|
if isResponse := dh.Bits&_QR != 0; isResponse {
|
||
|
|
return MsgIgnore
|
||
|
|
}
|
||
|
|
|
||
|
|
// Don't allow dynamic updates, because then the sections can contain a whole bunch of RRs.
|
||
|
|
opcode := int(dh.Bits>>11) & 0xF
|
||
|
|
if opcode != OpcodeQuery && opcode != OpcodeNotify {
|
||
|
|
return MsgRejectNotImplemented
|
||
|
|
}
|
||
|
|
|
||
|
|
if dh.Qdcount != 1 {
|
||
|
|
return MsgReject
|
||
|
|
}
|
||
|
|
// NOTIFY requests can have a SOA in the ANSWER section. See RFC 1996 Section 3.7 and 3.11.
|
||
|
|
if dh.Ancount > 1 {
|
||
|
|
return MsgReject
|
||
|
|
}
|
||
|
|
// IXFR request could have one SOA RR in the NS section. See RFC 1995, section 3.
|
||
|
|
if dh.Nscount > 1 {
|
||
|
|
return MsgReject
|
||
|
|
}
|
||
|
|
if dh.Arcount > 2 {
|
||
|
|
return MsgReject
|
||
|
|
}
|
||
|
|
return MsgAccept
|
||
|
|
}
|