feat: Set SSH env vars: SSH_CLIENT, SSH_CONNECTION and SSH_TTY

mafredri · mafredri · commit bab3c85d7bf2 · 2022-08-23T14:38:12.000+03:00
Fixes #2339
diff --git a/agent/agent.go b/agent/agent.go
@@ -427,6 +427,11 @@ func (a *agent) handleSSHSession(session ssh.Session) (retErr error) {
 	if err != nil {
 		return err
 	}
+	// Set SSH connection environment variables, from the clients perspective.
+	srcAddr, srcPort := addrToSSHEnvAddr(session.RemoteAddr())
+	dstAddr, dstPort := addrToSSHEnvAddr(session.LocalAddr())
+	cmd.Env = append(cmd.Env, fmt.Sprintf("SSH_CLIENT=%s %s %s", srcAddr, srcPort, dstPort))
+	cmd.Env = append(cmd.Env, fmt.Sprintf("SSH_CONNECTION=%s %s %s %s", srcAddr, srcPort, dstAddr, dstPort))
 
 	if ssh.AgentRequested(session) {
 		l, err := ssh.NewAgentListener()
@@ -441,6 +446,8 @@ func (a *agent) handleSSHSession(session ssh.Session) (retErr error) {
 	sshPty, windowSize, isPty := session.Pty()
 	if isPty {
 		cmd.Env = append(cmd.Env, fmt.Sprintf("TERM=%s", sshPty.Term))
+
+		// The pty package sets `SSH_TTY` on supported platforms.
 		ptty, process, err := pty.Start(cmd)
 		if err != nil {
 			return xerrors.Errorf("start command: %w", err)
@@ -695,6 +702,19 @@ func (a *agent) handleReconnectingPTY(ctx context.Context, rawID string, conn ne
 	}
 }
 
+// addrToSSHEnvAddr turns the address and port into space-separated values,
+// works with IPv4, IPv6 and invalid addresses (such as [peer/unknown-addr]).
+func addrToSSHEnvAddr(a net.Addr) (addr string, port string) {
+	addr = a.String()
+	port = "0"
+	li := strings.LastIndex(addr, ":")
+	if li != -1 {
+		port = addr[li+1:]
+		addr = addr[:li]
+	}
+	return addr, port
+}
+
 // dialResponse is written to datachannels with protocol "dial" by the agent as
 // the first packet to signify whether the dial succeeded or failed.
 type dialResponse struct {
diff --git a/pty/start_other.go b/pty/start_other.go
@@ -4,6 +4,7 @@
 package pty
 
 import (
+	"fmt"
 	"os/exec"
 	"runtime"
 	"strings"
@@ -18,6 +19,8 @@ func startPty(cmd *exec.Cmd) (PTY, Process, error) {
 	if err != nil {
 		return nil, nil, xerrors.Errorf("open: %w", err)
 	}
+
+	cmd.Env = append(cmd.Env, fmt.Sprintf("SSH_PTY=%s", tty.Name()))
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		Setsid:  true,
 		Setctty: true,
