Fix handleIndexError crash on throw null in query servers

[vamsi2246]

If an untrusted map function executes 'throw null', the check 'err[0] == "fatal"' evaluates 'null[0]' which throws an uncaught TypeError, fatally crashing the JavaScript worker process. This adds a null guard 'err && err[0]' to nouveau.js, views.js, and dreyfus.js.

[big-r81]

What is an "untrusted map function" and why would you do a "throw null"?

[rnewson]

(and noting that our mandatory form has been deleted. It needs to be restored and completely honestly before we could consider merging)

[rnewson]

noting that this just crashes things we expect to crash in such events, it's not a security finding or a DDOS finding. Still, it is nice to handle such things more politely.

[rnewson]

@big-r81 we deliberately do not trust any javascript map or reduce functions, they're entered by users. it's why they are executed in a sandbox.

[big-r81]

@big-r81 we deliberately do not trust any javascript map or reduce functions, they're entered by users. it's why they are executed in a sandbox.

I'm well aware of that 😉, I was just talking about the term itself — we're simply executing JavaScript code, whether it's trusted, untrusted or whatever ...