feat: validate ssh properties before launching workspaces

This was reported by a member in Discord, and displayed a poor error by VS Code
when it failed before.

Users cannot override our config options otherwise connections
may fail or have unexpected behavior.

Author: kylecarbs

src/remote.ts

@@ -20,7 +20,7 @@ import * as semver from "semver"
 import * as vscode from "vscode"
 import * as ws from "ws"
 import { SSHConfig, SSHValues, defaultSSHConfigResponse, mergeSSHConfigValues } from "./sshConfig"
-import { sshSupportsSetEnv } from "./sshSupport"
+import { computeSSHProperties, sshSupportsSetEnv } from "./sshSupport"
 import { Storage } from "./storage"
 
 export class Remote {
@@ -411,7 +411,7 @@ export class Remote {
     //
     // If we didn't write to the SSH config file, connecting would fail with
     // "Host not found".
-    await this.updateSSHConfig()
+    await this.updateSSHConfig(authorityParts[1])
 
     this.findSSHProcessID().then((pid) => {
       if (!pid) {
@@ -440,7 +440,7 @@ export class Remote {
 
   // updateSSHConfig updates the SSH configuration with a wildcard that handles
   // all Coder entries.
-  private async updateSSHConfig() {
+  private async updateSSHConfig(hostName: string) {
     let deploymentSSHConfig = defaultSSHConfigResponse
     try {
       const deploymentConfig = await getDeploymentSSHConfig()
@@ -528,6 +528,34 @@ export class Remote {
     }
 
     await sshConfig.update(sshValues, sshConfigOverrides)
+
+    // A user can provide a "Host *" entry in their SSH config to add options
+    // to all hosts. We need to ensure that the options we set are not
+    // overridden by the user's config.
+    const computedProperties = computeSSHProperties(hostName, sshConfig.getRaw())
+    const keysToMatch: Array<keyof SSHValues> = ["ProxyCommand", "UserKnownHostsFile", "StrictHostKeyChecking"]
+    for (let i = 0; i < keysToMatch.length; i++) {
+      const key = keysToMatch[i]
+      if (computedProperties[key] === sshValues[key]) {
+        continue
+      }
+
+      const result = await this.vscodeProposed.window.showErrorMessage(
+        "Unexpected SSH Config Option",
+        {
+          useCustom: true,
+          modal: true,
+          detail: `Your SSH config is overriding the "${key}" property to "${computedProperties[key]}" when it expected "${sshValues[key]}" for the "${hostName}" host. Please fix this and try again!`,
+        },
+        "Reload Window",
+      )
+      if (result === "Reload Window") {
+        await this.reloadWindow()
+      }
+      await this.closeRemote()
+    }
+
+    return sshConfig.getRaw()
   }
 
   // showNetworkUpdates finds the SSH process ID that is being used by this

src/sshSupport.test.ts

@@ -1,5 +1,5 @@
 import { it, expect } from "vitest"
-import { sshSupportsSetEnv, sshVersionSupportsSetEnv } from "./sshSupport"
+import { computeSSHProperties, sshSupportsSetEnv, sshVersionSupportsSetEnv } from "./sshSupport"
 
 const supports = {
   "OpenSSH_8.9p1 Ubuntu-3ubuntu0.1, OpenSSL 3.0.2 15 Mar 2022": true,
@@ -17,3 +17,23 @@ Object.entries(supports).forEach(([version, expected]) => {
 it("current shell supports ssh", () => {
   expect(sshSupportsSetEnv()).toBeTruthy()
 })
+
+it("computes the config for a host", () => {
+  const properties = computeSSHProperties(
+    "coder-vscode--testing",
+    `Host *
+  StrictHostKeyChecking yes
+
+# --- START CODER VSCODE ---
+Host coder-vscode--*
+  StrictHostKeyChecking no
+  Another=true
+# --- END CODER VSCODE ---
+`,
+  )
+
+  expect(properties).toEqual({
+    Another: "true",
+    StrictHostKeyChecking: "yes",
+  })
+})

src/sshSupport.ts

@@ -36,3 +36,55 @@ export function sshVersionSupportsSetEnv(sshVersionString: string): boolean {
   }
   return false
 }
+
+// computeSSHProperties accepts an SSH config and a host name and returns
+// the properties that should be set for that host.
+export function computeSSHProperties(host: string, config: string): Record<string, string> {
+  let currentConfig:
+    | {
+        Host: string
+        properties: Record<string, string>
+      }
+    | undefined
+  const configs: Array<typeof currentConfig> = []
+  config.split("\n").forEach((line) => {
+    line = line.trim()
+    if (line === "") {
+      return
+    }
+    const [key, ...valueParts] = line.split(/\s+|=/)
+    if (key.startsWith("#")) {
+      // Ignore comments!
+      return
+    }
+    if (key === "Host") {
+      if (currentConfig) {
+        configs.push(currentConfig)
+      }
+      currentConfig = {
+        Host: valueParts.join(" "),
+        properties: {},
+      }
+      return
+    }
+    if (!currentConfig) {
+      return
+    }
+    currentConfig.properties[key] = valueParts.join(" ")
+  })
+  if (currentConfig) {
+    configs.push(currentConfig)
+  }
+
+  const merged: Record<string, string> = {}
+  configs.reverse().forEach((config) => {
+    if (!config) {
+      return
+    }
+    if (!new RegExp("^" + config?.Host.replace(/\*/g, ".*") + "$").test(host)) {
+      return
+    }
+    Object.assign(merged, config.properties)
+  })
+  return merged
+}