Re: [PATCH 2/4] binder: migrate ioctl to new PF_SPAM_DETECTION

Carlos Llamas
2024-04-20T23:49:09Z

On Thu, Apr 18, 2024 at 08:12:22AM +0000, Alice Ryhl wrote:
> Carlos Llamas <cmllamas@google.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@google.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