lib: fix phantom EACCES on spawn in some environments

On some Linux environments (e.g. WSL), execvp may return EACCES instead
of ENOENT when a command is not found in PATH, if it encounters
permission errors during the search.

This change adds a check to verify if the file actually exists in PATH
when EACCES is received for a command without path separators. If not
found, the error is normalized to ENOENT.

Author: watilde

lib/internal/child_process.js

@@ -38,6 +38,8 @@ const {
 const EventEmitter = require('events');
 const net = require('net');
 const dgram = require('dgram');
+const fs = require('fs');
+const path = require('path');
 const inspect = require('internal/util/inspect').inspect;
 const assert = require('internal/assert');
 
@@ -73,6 +75,34 @@ const {
   UV_ESRCH,
 } = internalBinding('uv');
 
+function verifyENOENT(file, envPairs) {
+  if (file === '.' || file.includes(path.sep)) return false;
+  let envPath;
+  if (envPairs) {
+    for (let i = 0; i < envPairs.length; i++) {
+      const pair = envPairs[i];
+      if (pair.startsWith('PATH=')) {
+        envPath = pair.slice(5);
+        break;
+      }
+    }
+  }
+  if (!envPath) {
+    envPath = process.env.PATH;
+  }
+  if (!envPath) return false;
+  const paths = envPath.split(path.delimiter);
+  for (let i = 0; i < paths.length; i++) {
+    const p = paths[i];
+    if (!p) continue;
+    const fullPath = path.resolve(p, file);
+    if (fs.existsSync(fullPath)) {
+      return false;
+    }
+  }
+  return true;
+}
+
 const { SocketListSend, SocketListReceive } = SocketList;
 
 // Lazy loaded for startup performance and to allow monkey patching of
@@ -394,8 +424,9 @@ ChildProcess.prototype.spawn = function spawn(options) {
 
   const err = this._handle.spawn(options);
 
-  // Run-time errors should emit an error, not throw an exception.
-  if (err === UV_EACCES ||
+  if (err === UV_EACCES && verifyENOENT(this.spawnfile, options.envPairs)) {
+    process.nextTick(onErrorNT, this, UV_ENOENT);
+  } else if (err === UV_EACCES ||
       err === UV_EAGAIN ||
       err === UV_EMFILE ||
       err === UV_ENFILE ||
@@ -1088,6 +1119,10 @@ function maybeClose(subprocess) {
 function spawnSync(options) {
   const result = spawn_sync.spawn(options);
 
+  if (result.error === UV_EACCES && verifyENOENT(options.file, options.envPairs)) {
+    result.error = UV_ENOENT;
+  }
+
   if (result.output && options.encoding && options.encoding !== 'buffer') {
     for (let i = 0; i < result.output.length; i++) {
       if (!result.output[i])