Background node process corrupts terminal state with tcsetattr() on exit

[andersk]

• Version: v14.9.0
• Platform: NixOS 21.03, Linux 5.8.11 x86_64
• Subsystem: ResetStdio in src/node.cc

In Bash, run the following:

node -e 'setTimeout(() => {}, 2000)' & sleep 1

This launches node -e 'setTimeout(() => {}, 2000)' in the background and sleep 1 in the foreground. After 1 second, control returns to Bash. After 2 seconds, Node exits and corrupts Bash’s terminal state:

• the ↑, ↓, →, ← arrow keys start printing ^[[A, ^[[B, ^[[C, ^[[D instead of scrolling through the Bash history or moving the insert point,
• the Tab key starts moving the cursor 8 spaces forward instead of Tab-completing the command,
• Ctrl+A and Ctrl+E print ^A and ^E instead of jumping to the beginning and end of the command, etc.

This happens when the ResetStdio handler uses tcsetattr to “restore” the terminal to the state it was in when Node started (#24260). This interferes with Bash, which uses and expects a different terminal state than sleep 1.

(The bug is sometimes reproducible without the sleep 1 depending on whether Node records the initial terminal state before Bash updates it, but the sleep 1 makes it reliable.)

Normally, the terminal state would be protected from such undesired modifications by a background process: the kernel generates SIGTTOU to suspend the process until it’s brought to the foreground. But ResetStdio now deliberately overrides this protection by blocking SIGTTOU (#28535).

IMO, both #24260 and #28535 should be reverted. Node is a programming language; it should never make changes to the terminal state that programs did not request.

[gireeshpunathil]

able to reproduce in linux, not sure what implications are for reverting the two commits in the linked PR. tag. Tagging as a bug.

[graue]

This also reproduces in Node 20.5.1 and 18.16.1 by:

1. Run any Node.js process in the foreground
2. Ctrl-Z it
3. Background it by entering bg
4. The process subsequently exits while backgrounded

I have a probably unusual use case where I hit this a lot and it's frustrating (I wrote a simple music player using Node that exits after playing the song). I concur that the behavior should be changed.