From 473c3521d824149a1b6e528275fc00b0fb5012d2 Mon Sep 17 00:00:00 2001
From: Austin Kelleher <austinlkelleher@gmail.com>
Date: Fri, 8 Apr 2022 16:59:40 -0400
Subject: [PATCH] buffer: atob throw error when the input string is invalid

The specification of `atob` has various different conditions that we
need to abide by. The specific changes that were made:

* `atob` now immediately throws when `undefined`, `false`, or a `number`
  is supplied
* `atob` now strips ASCII whitespace before attempting to decode
* `atob` now validates that the code point's length divided by 4 leaves a
  remainder that is not 1

See: https://infra.spec.whatwg.org/#forgiving-base64-decode

Fixes: https://github.com/nodejs/node/issues/42646
---
 lib/buffer.js                   | 23 ++++++++++++++++++++++-
 test/parallel/test-btoa-atob.js |  9 +++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/lib/buffer.js b/lib/buffer.js
index 773d56572aa2a4..2b7536643ba95d 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -1259,7 +1259,28 @@ function atob(input) {
   if (arguments.length === 0) {
     throw new ERR_MISSING_ARGS('input');
   }
-  input = `${input}`;
+
+  if (input === undefined || input === false || typeof input === 'number') {
+    throw lazyDOMException(
+      'The string to be decoded is not correctly encoded.',
+      'ValidationError');
+  }
+
+  // Remove all ASCII whitespace from data.
+  //
+  // See #1 - https://infra.spec.whatwg.org/#forgiving-base64
+  input = `${input}`.replace(/\s/g, '');
+
+  // If data's code point length divides by 4 leaving a remainder of 1, then
+  // return failure.
+  //
+  // See #3 - https://infra.spec.whatwg.org/#forgiving-base64
+  if (input.length % 4 === 1) {
+    throw lazyDOMException(
+      'The string to be decoded is not correctly encoded.',
+      'ValidationError');
+  }
+
   for (let n = 0; n < input.length; n++) {
     if (!ArrayPrototypeIncludes(kForgivingBase64AllowedChars,
                                 StringPrototypeCharCodeAt(input, n)))
diff --git a/test/parallel/test-btoa-atob.js b/test/parallel/test-btoa-atob.js
index 64f53671030ba0..3a9786f7a62111 100644
--- a/test/parallel/test-btoa-atob.js
+++ b/test/parallel/test-btoa-atob.js
@@ -15,3 +15,12 @@ throws(() => buffer.btoa(), /TypeError/);
 
 strictEqual(atob(' '), '');
 strictEqual(atob('  YW\tJ\njZA=\r= '), 'abcd');
+
+throws(() => buffer.atob(undefined), /ValidationError/);
+throws(() => buffer.atob(false), /ValidationError/);
+throws(() => buffer.atob(1), /ValidationError/);
+throws(() => buffer.atob(0), /ValidationError/);
+throws(() => buffer.atob('a'), /ValidationError/);
+throws(() => buffer.atob('a '), /ValidationError/);
+throws(() => buffer.atob(' a'), /ValidationError/);
+throws(() => buffer.atob('aaaaa'), /ValidationError/);