linux-kernel - Re: [PATCH v2 1/2] i8k: Autodetect maximal fan speed and fan RPM multiplier

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Message-Id: <201412191951.25562@pali>
Date:	Fri, 19 Dec 2014 19:51:25 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Valdis.Kletnieks@...edu,
	Steven Honeyman <stevenhoneyman@...il.com>,
	Jean Delvare <jdelvare@...e.de>,
	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Jochen Eisinger <jochen@...guin-breeder.org>
Subject: Re: [PATCH v2 1/2] i8k: Autodetect maximal fan speed and fan RPM multiplier

On Friday 19 December 2014 19:32:37 Guenter Roeck wrote:
> > -static int i8k_fan_mult;
> > -static int i8k_pwm_mult;
> > -static int i8k_fan_max = I8K_FAN_HIGH;
> > +static int i8k_fan_mult[2];
> > +static int i8k_pwm_mult[2];
> > +static int i8k_fan_max[2];
> 
> The rationale for this change is not explained in the commit
> log.
> 
> Do you have any indication that those values would ever be
> different for the two fans, ie that you actually need arrays
> here ?
> 

I do not know... But if we decide to use only single value for 
multiplier and max value which fan to use for autodetection?

> > @@ -271,8 +274,25 @@ static int i8k_get_fan_speed(int fan)
> > 
> >  {
> >  
> >  	struct smm_regs regs = { .eax = I8K_SMM_GET_SPEED, };
> > 
> > +	if (fan < 0 || fan >= ARRAY_SIZE(i8k_fan_mult))
> > +		return -EINVAL;
> > +
> 
> This range check (and probably others) is still unnecessary.
> 
> Guenter
> 

No, it is necessary. Function i8k_get_fan_speed is called from 
ioctl callback with value which comes from userspace. If 
userspace specify fan out of that array we can get kernel panic.

> >  	regs.ebx = fan & 0xff;
> > 
> > -	return i8k_smm(&regs) ? : (regs.eax & 0xffff) *
> > i8k_fan_mult; +	return i8k_smm(&regs) ? : (regs.eax &
> > 0xffff) * i8k_fan_mult[fan]; +}

-- 
Pali Rohár
pali.rohar@...il.com

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