linux-kernel - Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs

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Message-ID: <202008271516.ED209B68@keescook>
Date:   Thu, 27 Aug 2020 15:16:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Joe Perches <joe@...ches.com>
Cc:     David Laight <David.Laight@...LAB.COM>,
        Julia Lawall <julia.lawall@...ia.fr>,
        Alex Dewar <alex.dewar90@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        cocci <cocci@...teme.lip6.fr>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        "accessrunner-general@...ts.sourceforge.net" 
        <accessrunner-general@...ts.sourceforge.net>
Subject: Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs

On Thu, Aug 27, 2020 at 03:11:57PM -0700, Joe Perches wrote:
> On Thu, 2020-08-27 at 22:03 +0000, David Laight wrote:
> > From: Joe Perches
> > > Sent: 27 August 2020 21:30
> > ...
> > > Perhaps what's necessary is to find any
> > > appropriate .show function and change
> > > any use of strcpy/sprintf within those
> > > function to some other name.
> > > 
> > > For instance:
> > > 
> > > drivers/isdn/mISDN/core.c-static ssize_t name_show(struct device *dev,
> > > drivers/isdn/mISDN/core.c-                       struct device_attribute *attr, char *buf)
> > > drivers/isdn/mISDN/core.c-{
> > > drivers/isdn/mISDN/core.c:      strcpy(buf, dev_name(dev));
> > > drivers/isdn/mISDN/core.c-      return strlen(buf);
> > > drivers/isdn/mISDN/core.c-}
> > > drivers/isdn/mISDN/core.c-static DEVICE_ATTR_RO(name);
> > 
> > That form ends up calculating the string length twice.
> > Better would be:
> > 	len = strlen(msg);
> > 	memcpy(buf, msg, len);
> > 	return len;
> 
> or given clang's requirement for stpcpy
> 
> 	return stpcpy(buf, dev_name(dev)) - buf;
> 
> (I do not advocate for this ;)

Heh. And humans aren't allowed to use stpcpy() in the kernel. :)

-- 
Kees Cook