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

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Message-ID: <20200825081752.hj3zyhg2qumzd64n@lenovo-laptop>
Date:   Tue, 25 Aug 2020 09:17:52 +0100
From:   Alex Dewar <alex.dewar90@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     'Alex Dewar' <alex.dewar90@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        "accessrunner-general@...ts.sourceforge.net" 
        <accessrunner-general@...ts.sourceforge.net>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: atm: don't use snprintf() for sysfs attrs

On Tue, Aug 25, 2020 at 08:12:05AM +0000, David Laight wrote:
> From: Alex Dewar
> > Sent: 24 August 2020 23:23
> > kernel/cpu.c: don't use snprintf() for sysfs attrs
> > 
> > As per the documentation (Documentation/filesystems/sysfs.rst),
> > snprintf() should not be used for formatting values returned by sysfs.
> > 
> > In all of these cases, sprintf() suffices as we know that the formatted
> > strings will be less than PAGE_SIZE in length.
> 
> Hmmmm....
> I much prefer to see bounded string ops.
> sysfs really ought to be passing through the buffer length.
> The buffer size should probably be SYSFS_BUF_LEN not PAGE_SIZE
> (even it happens to typically be the same).
> If PAGE_SIZE is big (or small) passing a 4k buffer may be
> more appropriate than a PAGE_SIZE one.
> 
> 	David

We could use scnprintf() instead I guess. But an expression like:
	return sprintf(buf, "%d\n", value);
will never overflow if buf is PAGE_SIZE, right...?

> 
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