fs: fix reads with pos > 4GB

PR-URL: #21003
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: mafintosh

lib/fs.js

@@ -593,7 +593,7 @@ fs.read = function(fd, buffer, offset, length, position, callback) {
 
   validateOffsetLengthRead(offset, length, buffer.length);
 
-  if (!isUint32(position))
+  if (!Number.isSafeInteger(position))
     position = -1;
 
   function wrapper(err, bytesRead) {
@@ -623,7 +623,7 @@ fs.readSync = function(fd, buffer, offset, length, position) {
 
   validateOffsetLengthRead(offset, length, buffer.length);
 
-  if (!isUint32(position))
+  if (!Number.isSafeInteger(position))
     position = -1;
 
   const ctx = {};

test/parallel/test-fs-read.js

@@ -53,3 +53,18 @@ test(Buffer.allocUnsafe(expected.length),
 test(new Uint8Array(expected.length),
      new Uint8Array(expected.length),
      Uint8Array.from(expected));
+
+{
+  // Reading beyond file length (3 in this case) should return no data.
+  // This is a test for a bug where reads > uint32 would return data
+  // from the current position in the file.
+  const fd = fs.openSync(filepath, 'r');
+  const pos = 0xffffffff + 1; // max-uint32 + 1
+  const nRead = fs.readSync(fd, Buffer.alloc(1), 0, 1, pos);
+  assert.strictEqual(nRead, 0);
+
+  fs.read(fd, Buffer.alloc(1), 0, 1, pos, common.mustCall((err, nRead) => {
+    assert.ifError(err);
+    assert.strictEqual(nRead, 0);
+  }));
+}