linux-kernel - Re: [PATCH 2/4] binder: migrate ioctl to new PF_SPAM

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Message-ID: <ZibjkV3aweBq4uVB@google.com>
Date: Mon, 22 Apr 2024 22:24:17 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: arve@...roid.com, brauner@...nel.org, gregkh@...uxfoundation.org,
	joel@...lfernandes.org, kernel-team@...roid.com,
	linux-kernel@...r.kernel.org, maco@...roid.com, surenb@...gle.com,
	tkjos@...roid.com
Subject: Re: [PATCH 2/4] binder: migrate ioctl to new PF_SPAM_DETECTION

On Mon, Apr 22, 2024 at 10:52:57AM +0200, Alice Ryhl wrote:
> On Sun, Apr 21, 2024 at 1:49 AM Carlos Llamas <cmllamas@...gle.com> wrote:
> >
> > On Thu, Apr 18, 2024 at 08:12:22AM +0000, Alice Ryhl wrote:
> > > Carlos Llamas <cmllamas@...gle.com> writes:
> > > > @@ -5553,7 +5553,8 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> > > >                     goto err;
> > > >             }
> > > >             binder_inner_proc_lock(proc);
> > > > -           proc->oneway_spam_detection_enabled = (bool)enable;
> > > > +           proc->flags &= ~PF_SPAM_DETECTION;
> > > > +           proc->flags |= enable & PF_SPAM_DETECTION;
> > >
> > > The bitwise and in `enable & PF_SPAM_DETECTION` only works because
> > > PF_SPAM_DETECTION happens to be equal to 1. This seems pretty fragile to
> > > me. Would you be willing to do this instead?
> > >
> > > proc->flags &= ~PF_SPAM_DETECTION;
> > > if (enable)
> > >       proc->flags |= PF_SPAM_DETECTION;
> > >
> >
> > I don't think it is fragile since PF_SPAM_DETECTION is fixed. However,
> > I agree the code is missing context about the flag being bit 0 and your
> > version addresses this problem. So I'll take it for v2, thanks!
> 
> Thanks! By fragile I mean that it could result in future mistakes,
> e.g. somebody could copy this code and use it elsewhere with a
> different bit flag that might not be bit 0.

Oh, I see. Yeah that would be a problem.

> 
> > > Carlos Llamas <cmllamas@...gle.com> writes:
> > > > -                   if (proc->oneway_spam_detection_enabled &&
> > > > -                              w->type == BINDER_WORK_TRANSACTION_ONEWAY_SPAM_SUSPECT)
> > > > +                   if (proc->flags & PF_SPAM_DETECTION &&
> > > > +                       w->type == BINDER_WORK_TRANSACTION_ONEWAY_SPAM_SUSPECT)
> > >
> > > Maybe I am just not sufficiently familiar with C, but I had to look up
> > > the operator precedence rules for this one. Could we add parenthesises
> > > around `proc->flags & PF_SPAM_DETECTION`? Or even define a macro for it?
> >
> > I think this is fairly common in C but I can definitly add the extra
> > paranthesis if it helps.
> 
> Yeah, makes sense. Thanks!
> 
> With the mentioned changes, you may add:
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

Done. Thanks!