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Revert "Take ownership of buffer in QueuePacketConn QueueIncoming/WriteTo."

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This reverts commit 839d221883. (Except for
the added benchmarks in queuepacketconn_test.go.) This change
corresponds to the issues #40187 and #40199.

The analysis in https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/issues/40199
was wrong; kcp-go does reuse the buffers it passes to
QueuePacketConn.WriteTo. This led to unsynchronized reuse of packet
buffers and mangled packets observable at the client:
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/issues/40260.

Undoing the change in QueuePacketConn.QueueIncoming as well, for
symmetry, even though it is not implicated in any correctness problems.
This commit is contained in:
David Fifield 2023-03-13 12:57:35 -06:00
parent b63d2272bf
commit d2858aeb7e
1 changed files with 13 additions and 9 deletions
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22
common/turbotunnel/queuepacketconn.go
View file

@ -42,9 +42,8 @@ func NewQueuePacketConn(localAddr net.Addr, timeout time.Duration) *QueuePacketC
}
}
// QueueIncoming queues an incoming packet and its source address, to be
// returned in a future call to ReadFrom. This function takes ownership of p and
// the caller must not reuse it.
// QueueIncoming queues and incoming packet and its source address, to be
// returned in a future call to ReadFrom.
func (c *QueuePacketConn) QueueIncoming(p []byte, addr net.Addr) {
select {
case <-c.closed:
@ -52,8 +51,11 @@ func (c *QueuePacketConn) QueueIncoming(p []byte, addr net.Addr) {
return
default:
}
// Copy the slice so that the caller may reuse it.
buf := make([]byte, len(p))
copy(buf, p)
select {
case c.recvQueue <- taggedPacket{p, addr}:
case c.recvQueue <- taggedPacket{buf, addr}:
default:
// Drop the incoming packet if the receive queue is full.
}
@ -82,20 +84,22 @@ func (c *QueuePacketConn) ReadFrom(p []byte) (int, net.Addr, error) {
}
// WriteTo queues an outgoing packet for the given address. The queue can later
// be retrieved using the OutgoingQueue method. This function takes ownership of
// p and the caller must not reuse it.
// be retrieved using the OutgoingQueue method.
func (c *QueuePacketConn) WriteTo(p []byte, addr net.Addr) (int, error) {
select {
case <-c.closed:
return 0, &net.OpError{Op: "write", Net: c.LocalAddr().Network(), Addr: c.LocalAddr(), Err: c.err.Load().(error)}
default:
}
// Copy the slice so that the caller may reuse it.
buf := make([]byte, len(p))
copy(buf, p)
select {
case c.clients.SendQueue(addr) <- p:
return len(p), nil
case c.clients.SendQueue(addr) <- buf:
return len(buf), nil
default:
// Drop the outgoing packet if the send queue is full.
return len(p), nil
return len(buf), nil
}
}