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

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Message-ID: <ZiRUcEtIypy1n4Xj@google.com>
Date: Sat, 20 Apr 2024 23:49:04 +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 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! 

> 
> 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.

--
Carlos Llamas