duffyduckandClaude Opus 5
9ed473a965
The HID failure came down to the endpoint type map being indexed by endpoint number without the direction bit. A composite device can have endpoint 1 as both interrupt IN (0x81) and bulk OUT (0x01); the last one read won, so interrupt URBs were submitted as bulk and the kernel rejected them. The device attached and stayed silent. Endpoint data now comes from the raw descriptors read from /dev/bus/usb rather than sysfs, which only ever exposes the active alternate setting — a webcam's isochronous endpoints are invisible there because they only exist after SET_INTERFACE. Two sysfs parsing bugs fell out of that too: the numeric endpoint attributes are hex without a prefix (wMaxPacketSize "0040" was read as 40, not 64), and bInterval was never read at all. Reliability: three places could freeze the whole process. The share path fed io.Pipe from the WebSocket read loop, so one slow USB transfer stalled every tunnel and the keepalives with them. The relay wrote to client sockets while holding the hub lock, so one peer that stopped reading blocked routing and registration for everyone. Control transfers ran inline in the protocol loop behind a 5s timeout. Also fixed: a use-after- free where a discarded URB's memory could be collected while the kernel still owned it, a reap loop that spun at 100% CPU on ioctl errors, a missing attach timeout, a double close(done) panic, and Hash[:8] in the relay's log line, which let a client with a short hash take the server down. Adds mode "both", so one client can offer and consume devices at once. The tunnel and client-left callbacks became multicast for it: as plain fields the second manager to register silently unhooked the first. Tunnel traffic is now AES-256-GCM end to end, on the relay path as well as directly. The key is derived from the three tokens, not from the group hash — the relay is told the hash, so a key derived from it would protect nothing from the one party in the middle. Group IDs are unchanged, so existing setups keep working; only clients configured without the tokens drop to unencrypted, relay-only operation. Peers now try to connect directly, with the relay supplying the public address neither side can determine for itself. Candidates are raced because an unreachable address hangs until timeout rather than refusing. Falling back to the relay is not an error. Platform reach: cross-compiled targets for ARM, MIPS and RISC-V (the Linux client needed no code changes — usbdevfs is not architecture specific), multi-arch Docker images, an Android bridge that accepts devices over SCM_RIGHTS because apps cannot open /dev/bus/usb, and macOS builds via system_profiler enumeration. Adds a Windows KMDF filter driver under driver/windows with its Go side. UNTESTED: it has never been compiled or run, needs the WDK to build and an EV certificate to distribute. Treat it as a starting point. Adds "usb-client diag": says per machine whether sharing and using are possible, what stands in the way, and what fixes it. Reports can be uploaded to a relay to get them off machines that are awkward to copy from. 96 tests, all green under -race. Builds for linux, windows and darwin on amd64 and arm64. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
77 lines
2.8 KiB
Go
77 lines
2.8 KiB
Go
// Package crypto derives the keys that protect tunnel traffic and provides
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// the authenticated framing used on direct peer-to-peer connections.
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package crypto
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import (
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"crypto/sha256"
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"encoding/hex"
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"fmt"
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"io"
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"strings"
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"golang.org/x/crypto/hkdf"
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)
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// keySize is the AES-256 key length.
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const keySize = 32
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// hkdfSalt separates this key schedule from any other use of the same tokens.
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const hkdfSalt = "usb-server/tunnel/v1"
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// TunnelSecret is the long-lived group secret derived from the three tokens.
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//
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// It deliberately is NOT the group hash. The relay is told the hash so it can
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// group clients, which means anyone running the relay knows it — using it to
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// encrypt would protect nothing from the party best positioned to look. The
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// tokens themselves never leave the client, and the hash is a SHA-256 of them,
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// so knowing the hash does not yield this secret.
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type TunnelSecret struct {
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master []byte
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}
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// DeriveTunnelSecret builds the group secret from the three tokens.
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// All three must be non-empty; a client configured with only the group hash
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// cannot participate in encrypted tunnels.
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func DeriveTunnelSecret(token1, token2, token3 string) (*TunnelSecret, error) {
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if token1 == "" || token2 == "" || token3 == "" {
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return nil, fmt.Errorf("all three tokens are required to derive the tunnel key")
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}
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// Same joining as the group hash, so both are bound to the same input.
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combined := strings.Join([]string{token1, token2, token3}, ":")
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master := make([]byte, keySize)
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r := hkdf.New(sha256.New, []byte(combined), []byte(hkdfSalt), []byte("master"))
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if _, err := io.ReadFull(r, master); err != nil {
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return nil, fmt.Errorf("deriving master key: %w", err)
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}
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return &TunnelSecret{master: master}, nil
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}
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// TunnelKey derives the key for one tunnel from its ID.
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//
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// Every tunnel gets a fresh random ID, so each connection gets a distinct key
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// and nonces can restart from zero without ever repeating a (key, nonce) pair.
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func (s *TunnelSecret) TunnelKey(tunnelID string) ([]byte, error) {
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key := make([]byte, keySize)
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r := hkdf.New(sha256.New, s.master, []byte(hkdfSalt), []byte("tunnel:"+tunnelID))
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if _, err := io.ReadFull(r, key); err != nil {
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return nil, fmt.Errorf("deriving tunnel key: %w", err)
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}
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return key, nil
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}
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// PeerToken produces a short value a peer can present to prove it knows the
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// group secret, bound to the given context string.
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//
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// This authenticates direct connections: the relay can tell two clients how to
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// reach each other, but it cannot forge this, so a peer that presents a valid
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// token really is a group member rather than whoever happens to reach the port.
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func (s *TunnelSecret) PeerToken(context string) string {
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r := hkdf.New(sha256.New, s.master, []byte(hkdfSalt), []byte("peer-token:"+context))
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token := make([]byte, 32)
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io.ReadFull(r, token)
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return hex.EncodeToString(token)
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}
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