Handle CORS requests (#6289)

vendor/golang.org/x/crypto/ssh/agent/client.go

@@ -25,10 +25,22 @@ import (
 	"math/big"
 	"sync"
 
+	"crypto"
 	"golang.org/x/crypto/ed25519"
 	"golang.org/x/crypto/ssh"
 )
 
+// SignatureFlags represent additional flags that can be passed to the signature
+// requests an defined in [PROTOCOL.agent] section 4.5.1.
+type SignatureFlags uint32
+
+// SignatureFlag values as defined in [PROTOCOL.agent] section 5.3.
+const (
+	SignatureFlagReserved SignatureFlags = 1 << iota
+	SignatureFlagRsaSha256
+	SignatureFlagRsaSha512
+)
+
 // Agent represents the capabilities of an ssh-agent.
 type Agent interface {
 	// List returns the identities known to the agent.
@@ -57,6 +69,26 @@ type Agent interface {
 	Signers() ([]ssh.Signer, error)
 }
 
+type ExtendedAgent interface {
+	Agent
+
+	// SignWithFlags signs like Sign, but allows for additional flags to be sent/received
+	SignWithFlags(key ssh.PublicKey, data []byte, flags SignatureFlags) (*ssh.Signature, error)
+
+	// Extension processes a custom extension request. Standard-compliant agents are not
+	// required to support any extensions, but this method allows agents to implement
+	// vendor-specific methods or add experimental features. See [PROTOCOL.agent] section 4.7.
+	// If agent extensions are unsupported entirely this method MUST return an
+	// ErrExtensionUnsupported error. Similarly, if just the specific extensionType in
+	// the request is unsupported by the agent then ErrExtensionUnsupported MUST be
+	// returned.
+	//
+	// In the case of success, since [PROTOCOL.agent] section 4.7 specifies that the contents
+	// of the response are unspecified (including the type of the message), the complete
+	// response will be returned as a []byte slice, including the "type" byte of the message.
+	Extension(extensionType string, contents []byte) ([]byte, error)
+}
+
 // ConstraintExtension describes an optional constraint defined by users.
 type ConstraintExtension struct {
 	// ExtensionName consist of a UTF-8 string suffixed by the
@@ -179,6 +211,23 @@ type constrainExtensionAgentMsg struct {
 	Rest []byte `ssh:"rest"`
 }
 
+// See [PROTOCOL.agent], section 4.7
+const agentExtension = 27
+const agentExtensionFailure = 28
+
+// ErrExtensionUnsupported indicates that an extension defined in
+// [PROTOCOL.agent] section 4.7 is unsupported by the agent. Specifically this
+// error indicates that the agent returned a standard SSH_AGENT_FAILURE message
+// as the result of a SSH_AGENTC_EXTENSION request. Note that the protocol
+// specification (and therefore this error) does not distinguish between a
+// specific extension being unsupported and extensions being unsupported entirely.
+var ErrExtensionUnsupported = errors.New("agent: extension unsupported")
+
+type extensionAgentMsg struct {
+	ExtensionType string `sshtype:"27"`
+	Contents      []byte
+}
+
 // Key represents a protocol 2 public key as defined in
 // [PROTOCOL.agent], section 2.5.2.
 type Key struct {
@@ -260,7 +309,7 @@ type client struct {
 
 // NewClient returns an Agent that talks to an ssh-agent process over
 // the given connection.
-func NewClient(rw io.ReadWriter) Agent {
+func NewClient(rw io.ReadWriter) ExtendedAgent {
 	return &client{conn: rw}
 }
 
@@ -268,6 +317,21 @@ func NewClient(rw io.ReadWriter) Agent {
 // unmarshaled into reply and replyType is set to the first byte of
 // the reply, which contains the type of the message.
 func (c *client) call(req []byte) (reply interface{}, err error) {
+	buf, err := c.callRaw(req)
+	if err != nil {
+		return nil, err
+	}
+	reply, err = unmarshal(buf)
+	if err != nil {
+		return nil, clientErr(err)
+	}
+	return reply, nil
+}
+
+// callRaw sends an RPC to the agent. On success, the raw
+// bytes of the response are returned; no unmarshalling is
+// performed on the response.
+func (c *client) callRaw(req []byte) (reply []byte, err error) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
@@ -284,18 +348,14 @@ func (c *client) call(req []byte) (reply interface{}, err error) {
 	}
 	respSize := binary.BigEndian.Uint32(respSizeBuf[:])
 	if respSize > maxAgentResponseBytes {
-		return nil, clientErr(err)
+		return nil, clientErr(errors.New("response too large"))
 	}
 
 	buf := make([]byte, respSize)
 	if _, err = io.ReadFull(c.conn, buf); err != nil {
 		return nil, clientErr(err)
 	}
-	reply, err = unmarshal(buf)
-	if err != nil {
-		return nil, clientErr(err)
-	}
-	return reply, err
+	return buf, nil
 }
 
 func (c *client) simpleCall(req []byte) error {
@@ -369,9 +429,14 @@ func (c *client) List() ([]*Key, error) {
 // Sign has the agent sign the data using a protocol 2 key as defined
 // in [PROTOCOL.agent] section 2.6.2.
 func (c *client) Sign(key ssh.PublicKey, data []byte) (*ssh.Signature, error) {
+	return c.SignWithFlags(key, data, 0)
+}
+
+func (c *client) SignWithFlags(key ssh.PublicKey, data []byte, flags SignatureFlags) (*ssh.Signature, error) {
 	req := ssh.Marshal(signRequestAgentMsg{
 		KeyBlob: key.Marshal(),
 		Data:    data,
+		Flags:   uint32(flags),
 	})
 
 	msg, err := c.call(req)
@@ -681,3 +746,44 @@ func (s *agentKeyringSigner) Sign(rand io.Reader, data []byte) (*ssh.Signature,
 	// The agent has its own entropy source, so the rand argument is ignored.
 	return s.agent.Sign(s.pub, data)
 }
+
+func (s *agentKeyringSigner) SignWithOpts(rand io.Reader, data []byte, opts crypto.SignerOpts) (*ssh.Signature, error) {
+	var flags SignatureFlags
+	if opts != nil {
+		switch opts.HashFunc() {
+		case crypto.SHA256:
+			flags = SignatureFlagRsaSha256
+		case crypto.SHA512:
+			flags = SignatureFlagRsaSha512
+		}
+	}
+	return s.agent.SignWithFlags(s.pub, data, flags)
+}
+
+// Calls an extension method. It is up to the agent implementation as to whether or not
+// any particular extension is supported and may always return an error. Because the
+// type of the response is up to the implementation, this returns the bytes of the
+// response and does not attempt any type of unmarshalling.
+func (c *client) Extension(extensionType string, contents []byte) ([]byte, error) {
+	req := ssh.Marshal(extensionAgentMsg{
+		ExtensionType: extensionType,
+		Contents:      contents,
+	})
+	buf, err := c.callRaw(req)
+	if err != nil {
+		return nil, err
+	}
+	if len(buf) == 0 {
+		return nil, errors.New("agent: failure; empty response")
+	}
+	// [PROTOCOL.agent] section 4.7 indicates that an SSH_AGENT_FAILURE message
+	// represents an agent that does not support the extension
+	if buf[0] == agentFailure {
+		return nil, ErrExtensionUnsupported
+	}
+	if buf[0] == agentExtensionFailure {
+		return nil, errors.New("agent: generic extension failure")
+	}
+
+	return buf, nil
+}