fs: validate the input data to be of expected types

The input was not validated so far and that caused unwanted side
effects. E.g., `undefined` became the string `'undefined'`. It was
expected to fail or to end up as empty string.
Now all input is validated to be either some type of array buffer
view or a string. That way it's always clear what the user intents.

PR-URL: https://github.com/nodejs/node/pull/31030
Fixes: https://github.com/nodejs/node/issues/31025
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

2 files changed, 23 insertions, 10 deletions

diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
index e0c4e2ca4a4..6517a5ef4be 100644
--- a/lib/internal/fs/promises.js
+++ b/lib/internal/fs/promises.js
@@ -26,7 +26,7 @@ const {
   ERR_INVALID_ARG_VALUE,
   ERR_METHOD_NOT_IMPLEMENTED
 } = require('internal/errors').codes;
-const { isUint8Array } = require('internal/util/types');
+const { isArrayBufferView } = require('internal/util/types');
 const { rimrafPromises } = require('internal/fs/rimraf');
 const {
   copyObject,
@@ -44,6 +44,7 @@ const {
   validateOffsetLengthRead,
   validateOffsetLengthWrite,
   validateRmdirOptions,
+  validateStringAfterArrayBufferView,
   warnOnNonPortableTemplate
 } = require('internal/fs/utils');
 const { opendir } = require('internal/fs/dir');
@@ -140,16 +141,18 @@ function validateFileHandle(handle) {
 }
 
 async function writeFileHandle(filehandle, data, options) {
-  let buffer = isUint8Array(data) ?
-    data : Buffer.from('' + data, options.encoding || 'utf8');
-  let remaining = buffer.length;
+  if (!isArrayBufferView(data)) {
+    validateStringAfterArrayBufferView(data, 'data');
+    data = Buffer.from(data, options.encoding || 'utf8');
+  }
+  let remaining = data.length;
   if (remaining === 0) return;
   do {
     const { bytesWritten } =
-      await write(filehandle, buffer, 0,
-                  MathMin(16384, buffer.length));
+      await write(filehandle, data, 0,
+                  MathMin(16384, data.length));
     remaining -= bytesWritten;
-    buffer = buffer.slice(bytesWritten);
+    data = data.slice(bytesWritten);
   } while (remaining > 0);
 }
 
@@ -260,7 +263,7 @@ async function write(handle, buffer, offset, length, position) {
   if (buffer.length === 0)
     return { bytesWritten: 0, buffer };
 
-  if (isUint8Array(buffer)) {
+  if (isArrayBufferView(buffer)) {
     if (offset == null) {
       offset = 0;
     } else {
@@ -277,8 +280,7 @@ async function write(handle, buffer, offset, length, position) {
     return { bytesWritten, buffer };
   }
 
-  if (typeof buffer !== 'string')
-    buffer += '';
+  validateStringAfterArrayBufferView(buffer, 'buffer');
   const bytesWritten = (await binding.writeString(handle.fd, buffer, offset,
                                                   length, kUsePromises)) || 0;
   return { bytesWritten, buffer };
diff --git a/lib/internal/fs/utils.js b/lib/internal/fs/utils.js
index 18d8e07d78e..763a940f6e9 100644
--- a/lib/internal/fs/utils.js
+++ b/lib/internal/fs/utils.js
@@ -651,6 +651,16 @@ const getValidMode = hideStackFrames((mode, type) => {
     'mode', `an integer >= ${min} && <= ${max}`, mode);
 });
 
+const validateStringAfterArrayBufferView = hideStackFrames((buffer, name) => {
+  if (typeof buffer !== 'string') {
+    throw new ERR_INVALID_ARG_TYPE(
+      name,
+      ['string', 'Buffer', 'TypedArray', 'DataView'],
+      buffer
+    );
+  }
+});
+
 module.exports = {
   assertEncoding,
   BigIntStats,  // for testing
@@ -675,5 +685,6 @@ module.exports = {
   validateOffsetLengthWrite,
   validatePath,
   validateRmdirOptions,
+  validateStringAfterArrayBufferView,
   warnOnNonPortableTemplate
 };