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9206e766ed
The first packet fragment guard had an additional guard clause that was incorrectly comparing a length in bytes to a length in octets, and was also comparing what should have been an entire IPv4 through transport header length to a subprotocol payload length. The subprotocol header size guards were otherwise protecting against short transport headers, as is the conservative non-first fragment minimum offset size. Add an explicit disallowing of fragmentation for TSMP for the avoidance of doubt. Updates #cleanup Updates #5727 Signed-off-by: James Tucker <james@tailscale.com>
68 lines
1.9 KiB
Go
68 lines
1.9 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package packet
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import (
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"errors"
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"math"
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)
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const igmpHeaderLength = 8
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const tcpHeaderLength = 20
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const sctpHeaderLength = 12
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// maxPacketLength is the largest length that all headers support.
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// IPv4 headers using uint16 for this forces an upper bound of 64KB.
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const maxPacketLength = math.MaxUint16
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var (
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// errSmallBuffer is returned when Marshal receives a buffer
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// too small to contain the header to marshal.
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errSmallBuffer = errors.New("buffer too small")
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// errLargePacket is returned when Marshal receives a payload
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// larger than the maximum representable size in header
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// fields.
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errLargePacket = errors.New("packet too large")
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)
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// Header is a packet header capable of marshaling itself into a byte
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// buffer.
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type Header interface {
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// Len returns the length of the marshaled packet.
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Len() int
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// Marshal serializes the header into buf, which must be at
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// least Len() bytes long. Implementations of Marshal assume
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// that bytes after the first Len() are payload bytes for the
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// purpose of computing length and checksum fields. Marshal
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// implementations must not allocate memory.
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Marshal(buf []byte) error
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}
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// HeaderChecksummer is implemented by Header implementations that
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// need to do a checksum over their payloads.
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type HeaderChecksummer interface {
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Header
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// WriteCheck writes the correct checksum into buf, which should
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// be be the already-marshalled header and payload.
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WriteChecksum(buf []byte)
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}
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// Generate generates a new packet with the given Header and
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// payload. This function allocates memory, see Header.Marshal for an
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// allocation-free option.
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func Generate(h Header, payload []byte) []byte {
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hlen := h.Len()
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buf := make([]byte, hlen+len(payload))
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copy(buf[hlen:], payload)
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h.Marshal(buf)
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if hc, ok := h.(HeaderChecksummer); ok {
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hc.WriteChecksum(buf)
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}
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return buf
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}
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