linux-kernel - Re: [PATCH v7 4/4] pinctrl: Implementation of the generic scmi-pinctrl driver

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Date: Tue, 2 Apr 2024 17:09:34 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: "Peng Fan (OSS)" <peng.fan@....nxp.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Cristian Marussi <cristian.marussi@....com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-gpio@...r.kernel.org,
	Peng Fan <peng.fan@....com>,
	Oleksii Moisieiev <oleksii_moisieiev@...m.com>
Subject: Re: [PATCH v7 4/4] pinctrl: Implementation of the generic
 scmi-pinctrl driver

On Tue, Apr 02, 2024 at 04:22:45PM +0300, Andy Shevchenko wrote:
> On Tue, Apr 02, 2024 at 10:22:24AM +0800, Peng Fan (OSS) wrote:
> > +static int pinctrl_scmi_get_pins(struct scmi_pinctrl *pmx,
> > +				 struct pinctrl_desc *desc)
> > +{
> > +	struct pinctrl_pin_desc *pins;
> > +	unsigned int npins;
> > +	int ret, i;
> > +
> > +	npins = pinctrl_ops->count_get(pmx->ph, PIN_TYPE);
> > +	/*
> > +	 * npins will never be zero, the scmi pinctrl driver has bailed out
> > +	 * if npins is zero.
> > +	 */
> 
> This is fragile, but at least it is documented.
> 

It was never clear to me where the crash would happen if npins was zero.
Does some part of pinctrl internals assume we have at least one pin?

It's nice to be able to allocate zero element arrays and generally it
works well in the kernel.  The one common bug with zero element arrays
has to do with strings.  Something like this (garbage) example:

	str = kmalloc(n_char, GFP_KERNEL);
	copy_from_user(str, user_ptr, n_char);
	str[n_char - 1] = '\0';

If the str is zero bytes long it will lead to an Oops when we add a NUL
terminator.

regards,
dan carpenter