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Enable SSH agent support on Windows #1008
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,27 @@ | ||
| //go:build !windows | ||
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| package agent | ||
|
|
||
| import ( | ||
| "os" | ||
|
|
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| "golang.org/x/crypto/ssh" | ||
| gosshagent "golang.org/x/crypto/ssh/agent" | ||
| ) | ||
|
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| func GetSSHAuthSocket() string { | ||
| sshAuthSocket := os.Getenv("SSH_AUTH_SOCK") | ||
| if sshAuthSocket != "" { | ||
| return sshAuthSocket | ||
| } | ||
|
|
||
| return "" | ||
| } | ||
|
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| func ForwardToRemote(client *ssh.Client, addr string) error { | ||
| return gosshagent.ForwardToRemote(client, addr) | ||
| } | ||
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|
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| func RequestAgentForwarding(session *ssh.Session) error { | ||
| return gosshagent.RequestAgentForwarding(session) | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| package agent | ||
|
|
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| import ( | ||
| "io" | ||
| "os" | ||
| "strings" | ||
| "sync" | ||
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| "github.com/pkg/errors" | ||
| "golang.org/x/crypto/ssh" | ||
| gosshagent "golang.org/x/crypto/ssh/agent" | ||
| "gopkg.in/natefinch/npipe.v2" | ||
| ) | ||
|
|
||
| const ( | ||
| channelType = "[email protected]" | ||
| defaultNamedPipe = "\\\\.\\pipe\\openssh-ssh-agent" | ||
| ) | ||
|
|
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| /* | ||
| * Cygwin/MSYS2 `SSH_AUTH_SOCK` implementations from ssh-agent(1) are performed using an | ||
| * emulated socket rather than a true AF_UNIX socket. As such, those implementations are | ||
| * incompatible and a user should either utilize the Win32-OpenSSH implementation found | ||
| * in Windows 10/11 or utilize another alternative that support valid AF_UNIX sockets. | ||
| */ | ||
| func GetSSHAuthSocket() string { | ||
| sshAuthSocket := os.Getenv("SSH_AUTH_SOCK") | ||
| if sshAuthSocket != "" { | ||
| return sshAuthSocket | ||
| } | ||
| if _, err := os.Stat(defaultNamedPipe); err == nil { | ||
| return defaultNamedPipe | ||
| } | ||
|
|
||
| return "" | ||
| } | ||
|
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| func ForwardToRemote(client *ssh.Client, addr string) error { | ||
| if strings.Contains(addr, "\\\\.\\pipe\\") { | ||
| channels := client.HandleChannelOpen(channelType) | ||
| if channels == nil { | ||
| return errors.New("agent: already have handler for " + channelType) | ||
| } | ||
| conn, err := npipe.Dial(addr) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| conn.Close() | ||
|
|
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| go func() { | ||
| for ch := range channels { | ||
| channel, reqs, err := ch.Accept() | ||
| if err != nil { | ||
| continue | ||
| } | ||
| go ssh.DiscardRequests(reqs) | ||
| go forwardNamedPipe(channel, addr) | ||
| } | ||
| }() | ||
| return nil | ||
| } | ||
| return gosshagent.ForwardToRemote(client, addr) | ||
| } | ||
|
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| func RequestAgentForwarding(session *ssh.Session) error { | ||
| return gosshagent.RequestAgentForwarding(session) | ||
| } | ||
|
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| func forwardNamedPipe(channel ssh.Channel, addr string) { | ||
| conn, err := npipe.Dial(addr) | ||
| if err != nil { | ||
| return | ||
| } | ||
|
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| var wg sync.WaitGroup | ||
| wg.Add(2) | ||
| go func() { | ||
| io.Copy(conn, channel) | ||
| wg.Done() | ||
| }() | ||
| go func() { | ||
| io.Copy(channel, conn) | ||
| channel.CloseWrite() | ||
| wg.Done() | ||
| }() | ||
|
|
||
| wg.Wait() | ||
| conn.Close() | ||
| channel.Close() | ||
| } | ||
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I'm planning to test this just a little bit more tomorrow, but presently I know this works with the OpenSSH agent that ships with Windows 10/11 natively. I'm pretty sure that the Git for Windows variation utilizes a unix socket which would mean a slight adjustment to the agent forwarding to ensure the correct socket type is used for the connection.
More specifically, the OpenSSH build that comes built into Windows 10/11 creates a named pipe at
\\.\pipe\openssh-ssh-agentwhich is what I've defined as a constant above here. This pipe is hardcoded in the Microsoft OpenSSH build and is used by default when connecting to the agent.The Git for Windows build on the other hand is creating its files in the TEMP directory.
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I've confirmed that Git for Windows is in fact using an
AF_UNIXsocket, so I'll update the forward method just a little bit to handle that.There was a problem hiding this comment.
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After some more digging after being puzzled why I couldn't connect using the AF_UNIX socket type as directly utilized by the upstream
golang.org/x/crypto/ssh/agent, I've come to find out that MSYS2 which Git for Windows is based on uses an emulated socket rather than a native AF_UNIX socket as I was led to believe.Now with this said, there are a myriad of authenticators that do create valid AF_UNIX sockets for Windows and I found a PR for Win32-OpenSSH to add native AF_UNIX sockets to the build that comes packaged with Windows. Unfortunately, that PR is not yet merged.
What I think I'm going to do here is to prefer a set SSH_AUTH_SOCK, this way various correct implementations work, then fallback to the named pipe implementation, then finally return an error. When Windows finally natively supports SSH_AUTH_SOCK definitions, then the code will natively migrate to that updated path this way.
I'll submit this small change tomorrow, but then this should be good to go.