78 lines
1.7 KiB
Go
78 lines
1.7 KiB
Go
package vpnruntime
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import "encoding/binary"
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func normalizeIPv4PacketChecksums(packet []byte) bool {
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if len(packet) < 20 || packet[0]>>4 != 4 {
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return false
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}
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ihl := int(packet[0]&0x0f) * 4
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if ihl < 20 || len(packet) < ihl {
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return false
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}
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totalLen := int(binary.BigEndian.Uint16(packet[2:4]))
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if totalLen <= 0 || totalLen > len(packet) {
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totalLen = len(packet)
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}
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if totalLen < ihl {
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return false
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}
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packet[10], packet[11] = 0, 0
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binary.BigEndian.PutUint16(packet[10:12], checksum(packet[:ihl]))
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proto := packet[9]
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payload := packet[ihl:totalLen]
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switch proto {
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case 6:
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if len(payload) < 20 {
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return true
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}
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payload[16], payload[17] = 0, 0
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binary.BigEndian.PutUint16(payload[16:18], transportChecksum(packet, payload, proto))
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case 17:
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if len(payload) < 8 {
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return true
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}
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payload[6], payload[7] = 0, 0
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sum := transportChecksum(packet, payload, proto)
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if sum == 0 {
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sum = 0xffff
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}
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binary.BigEndian.PutUint16(payload[6:8], sum)
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case 1:
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if len(payload) < 4 {
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return true
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}
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payload[2], payload[3] = 0, 0
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binary.BigEndian.PutUint16(payload[2:4], checksum(payload))
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}
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return true
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}
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func transportChecksum(ipHeader []byte, payload []byte, proto byte) uint16 {
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pseudo := make([]byte, 12+len(payload))
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copy(pseudo[0:4], ipHeader[12:16])
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copy(pseudo[4:8], ipHeader[16:20])
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pseudo[8] = 0
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pseudo[9] = proto
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binary.BigEndian.PutUint16(pseudo[10:12], uint16(len(payload)))
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copy(pseudo[12:], payload)
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return checksum(pseudo)
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}
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func checksum(data []byte) uint16 {
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var sum uint32
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for len(data) >= 2 {
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sum += uint32(binary.BigEndian.Uint16(data[:2]))
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data = data[2:]
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}
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if len(data) == 1 {
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sum += uint32(data[0]) << 8
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}
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for (sum >> 16) != 0 {
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sum = (sum & 0xffff) + (sum >> 16)
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}
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return ^uint16(sum)
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}
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