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net/packet: add TCPFlag type and some more constants

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Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2021-01-11 20:17:13 -08:00
parent ad3fb6125d
commit 5eeaea9ef9
2 changed files with 13 additions and 8 deletions
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17
net/packet/packet.go
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@ -17,10 +17,15 @@
// RFC1858: prevent overlapping fragment attacks.
const minFrag = 60 + 20 // max IPv4 header + basic TCP header
type TCPFlag uint8
const (
TCPSyn = 0x02
TCPAck = 0x10
TCPSynAck = TCPSyn | TCPAck
TCPFin TCPFlag = 0x01
TCPSyn TCPFlag = 0x02
TCPRst TCPFlag = 0x04
TCPPsh TCPFlag = 0x08
TCPAck TCPFlag = 0x10
TCPSynAck TCPFlag = TCPSyn | TCPAck
)
// Parsed is a minimal decoding of a packet suitable for use in filters.
@ -46,7 +51,7 @@ type Parsed struct {
// DstIP4 is the destination address. Family matches IPVersion.
Dst netaddr.IPPort
// TCPFlags is the packet's TCP flag bigs. Valid iff IPProto == TCP.
TCPFlags uint8
TCPFlags TCPFlag
}
func (p *Parsed) String() string {
@ -186,7 +191,7 @@ func (q *Parsed) decode4(b []byte) {
}
q.Src.Port = binary.BigEndian.Uint16(sub[0:2])
q.Dst.Port = binary.BigEndian.Uint16(sub[2:4])
q.TCPFlags = sub[13] & 0x3F
q.TCPFlags = TCPFlag(sub[13]) & 0x3F
headerLength := (sub[12] & 0xF0) >> 2
q.dataofs = q.subofs + int(headerLength)
return
@ -274,7 +279,7 @@ func (q *Parsed) decode6(b []byte) {
}
q.Src.Port = binary.BigEndian.Uint16(sub[0:2])
q.Dst.Port = binary.BigEndian.Uint16(sub[2:4])
q.TCPFlags = sub[13] & 0x3F
q.TCPFlags = TCPFlag(sub[13]) & 0x3F
headerLength := (sub[12] & 0xF0) >> 2
q.dataofs = q.subofs + int(headerLength)
return

4
wgengine/filter/filter_test.go
View File

@ -414,7 +414,7 @@ func raw6(proto packet.IPProto, src, dst string, sport, dport uint16, trimLen in
payload := make([]byte, 12)
// Set the right bit to look like a TCP SYN, if the packet ends up interpreted as TCP
payload[5] = packet.TCPSyn
payload[5] = byte(packet.TCPSyn)
b := packet.Generate(&u, payload) // payload large enough to possibly be TCP
@ -443,7 +443,7 @@ func raw4(proto packet.IPProto, src, dst string, sport, dport uint16, trimLength
payload := make([]byte, 12)
// Set the right bit to look like a TCP SYN, if the packet ends up interpreted as TCP
payload[5] = packet.TCPSyn
payload[5] = byte(packet.TCPSyn)
b := packet.Generate(&u, payload) // payload large enough to possibly be TCP