Re: [PATCH] hwrng: core - Add WARN_ON for buggy read return values

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Mon Sep 23, 2024 at 12:26 PM EEST, Herbert Xu wrote:
 > > +
> > > +		err = rng->read(rng, buffer, size, wait);
> > > +		if (WARN_ON_ONCE(err > 0 && err > size))
> > 
> > Are you sure you want to use WARN_ON_ONCE here instead of
> > pr_warn_once()? I.e. is it worth of taking down the whole
> > kernel?
>
> Absolutely.  If this triggers it's a serious kernel bug and we
> should gather as much information as possible.  pr_warn_once is
> not the same thing as WARN_ON_ONCE in terms of what it prints.

Personally I allow the use of WARN only as the last resort.

If you need stack printout you can always use dump_stack().

>
> If people want to turn WARNs into BUGs, then they've only got
> themselves to blame when the kernel goes down.  On the other
> hand perhaps they *do* want this to panic and we should hand
> it to them.

Actually when you turn on "panic_on_warn" the user expectation is and
should be that the sites where WARN is used have been hand picked with
consideration so that panic happens for a reason.

This has also been denoted repeatedly by Greg:

https://lore.kernel.org/linux-cve-announce/2024061828-CVE-2024-36975-6719@gregkh/

I should check this somewhere but actually these days a wrongly chosen
WARN() might lead to CVE entry. That fix was by me but I never created
the CVE.

Greg, did we have something under Documentation/ that would fully
address the use of WARN?

BR, Jarkko