Closed
Description
This code is unsafe when worker threads are active:
node/src/node_process_methods.cc
Lines 248 to 249 in 40b559a
The umask(0) call temporarily changes the process-wide umask and races with fs operations from other threads.
Test case:
'use strict';
const { Worker, isMainThread } = require('worker_threads');
const { statSync, writeFileSync, unlinkSync } = require('fs');
function pummel() {
for (let i = 0; i < 1e4; i++) process.umask();
setImmediate(pummel);
}
if (isMainThread) {
process.umask(0o22);
new Worker(__filename);
pummel();
} else {
const file = 'x.txt';
for (;;) {
writeFileSync(file, 'ok', { mode: 0o666 });
const s = statSync(file);
s.mode &= 0o777;
if (0o644 !== s.mode) throw 'unexpected mode: ' + s.mode.toString(8);
unlinkSync(file);
}
}Fails within a few iterations with unexpected mode: 666
process.umask() (no arg) is allowed in workers so this test case works both ways.
This bug is potentially a security issue.