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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package fragmentation
import (
"container/heap"
"fmt"
"math"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
type hole struct {
first uint16
last uint16
filled bool
}
type reassembler struct {
reassemblerEntry
id FragmentID
size int
proto uint8
mu sync.Mutex
holes []hole
filled int
heap fragHeap
done bool
creationTime int64
pkt *stack.PacketBuffer
}
func newReassembler(id FragmentID, clock tcpip.Clock) *reassembler {
r := &reassembler{
id: id,
holes: make([]hole, 0, 16),
heap: make(fragHeap, 0, 8),
creationTime: clock.NowMonotonic(),
}
r.holes = append(r.holes, hole{
first: 0,
last: math.MaxUint16,
filled: false,
})
return r
}
// updateHoles updates the list of holes for an incoming fragment. It returns
// true if the fragment fits, it is not a duplicate and it does not overlap with
// another fragment.
//
// For IPv6, overlaps with an existing fragment are explicitly forbidden by
// RFC 8200 section 4.5:
// If any of the fragments being reassembled overlap with any other fragments
// being reassembled for the same packet, reassembly of that packet must be
// abandoned and all the fragments that have been received for that packet
// must be discarded, and no ICMP error messages should be sent.
//
// It is not explicitly forbidden for IPv4, but to keep parity with Linux we
// disallow it as well:
// https://github.com/torvalds/linux/blob/38525c6/net/ipv4/inet_fragment.c#L349
func (r *reassembler) updateHoles(first, last uint16, more bool) (bool, error) {
for i := range r.holes {
currentHole := &r.holes[i]
if currentHole.filled || last < currentHole.first || currentHole.last < first {
continue
}
if first < currentHole.first || currentHole.last < last {
// Incoming fragment only partially fits in the free hole.
return false, ErrFragmentOverlap
}
r.filled++
if first > currentHole.first {
r.holes = append(r.holes, hole{
first: currentHole.first,
last: first - 1,
filled: false,
})
}
if last < currentHole.last && more {
r.holes = append(r.holes, hole{
first: last + 1,
last: currentHole.last,
filled: false,
})
}
// Update the current hole to precisely match the incoming fragment.
r.holes[i] = hole{
first: first,
last: last,
filled: true,
}
return true, nil
}
// Incoming fragment is a duplicate/subset, or its offset comes after the end
// of the reassembled payload.
return false, nil
}
func (r *reassembler) process(first, last uint16, more bool, proto uint8, pkt *stack.PacketBuffer) (buffer.VectorisedView, uint8, bool, int, error) {
r.mu.Lock()
defer r.mu.Unlock()
if r.done {
// A concurrent goroutine might have already reassembled
// the packet and emptied the heap while this goroutine
// was waiting on the mutex. We don't have to do anything in this case.
return buffer.VectorisedView{}, 0, false, 0, nil
}
used, err := r.updateHoles(first, last, more)
if err != nil {
return buffer.VectorisedView{}, 0, false, 0, fmt.Errorf("fragment reassembly failed: %w", err)
}
var consumed int
if used {
// For IPv6, it is possible to have different Protocol values between
// fragments of a packet (because, unlike IPv4, the Protocol is not used to
// identify a fragment). In this case, only the Protocol of the first
// fragment must be used as per RFC 8200 Section 4.5.
//
// TODO(gvisor.dev/issue/3648): During reassembly of an IPv6 packet, IP
// options received in the first fragment should be used - and they should
// override options from following fragments.
if first == 0 {
r.pkt = pkt
r.proto = proto
}
vv := pkt.Data
// We store the incoming packet only if it filled some holes.
heap.Push(&r.heap, fragment{offset: first, vv: vv.Clone(nil)})
consumed = vv.Size()
r.size += consumed
}
// Check if all the holes have been filled and we are ready to reassemble.
if r.filled < len(r.holes) {
return buffer.VectorisedView{}, 0, false, consumed, nil
}
res, err := r.heap.reassemble()
if err != nil {
return buffer.VectorisedView{}, 0, false, 0, fmt.Errorf("fragment reassembly failed: %w", err)
}
return res, r.proto, true, consumed, nil
}
func (r *reassembler) checkDoneOrMark() bool {
r.mu.Lock()
prev := r.done
r.done = true
r.mu.Unlock()
return prev
}
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