From: David Laight <David.Laight@ACULAB.COM>
To: 'Alex Dewar' <alex.dewar90@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
"accessrunner-general@lists.sourceforge.net"
<accessrunner-general@lists.sourceforge.net>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] usb: atm: don't use snprintf() for sysfs attrs
Date: Tue, 25 Aug 2020 09:07:47 +0000 [thread overview]
Message-ID: <0d32d8092289498a9702b76d44074017@AcuMS.aculab.com> (raw)
In-Reply-To: <20200825081752.hj3zyhg2qumzd64n@lenovo-laptop>
From: Alex Dewar
> Sent: 25 August 2020 09:18
> 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...?
Certainly the return value from snprintf() isn't what you
want here (it almost never is) - so scnprintf() is much better.
A simple "%d" or "%u" wont overflow, but a "%s" might (even
if it is really expected that it shouldn't).
Even a "%*d" can go horribly wrong.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-08-25 9:07 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-24 22:23 [PATCH] usb: atm: don't use snprintf() for sysfs attrs Alex Dewar
2020-08-25 8:12 ` David Laight
2020-08-25 8:17 ` Alex Dewar
2020-08-25 9:07 ` David Laight [this message]
2020-08-25 8:24 ` Greg Kroah-Hartman
2020-08-27 16:49 ` Kees Cook
2020-08-27 17:45 ` Greg Kroah-Hartman
2020-08-27 6:42 ` Rasmus Villemoes
2020-08-27 7:15 ` Greg Kroah-Hartman
2020-08-27 13:18 ` Alex Dewar
2020-08-27 13:41 ` Rasmus Villemoes
2020-08-27 14:48 ` Alex Dewar
2020-08-27 16:58 ` Joe Perches
2020-08-27 19:42 ` [Cocci] " Julia Lawall
2020-08-27 20:29 ` Joe Perches
2020-08-27 21:00 ` Joe Perches
2020-08-27 21:29 ` Julia Lawall
2020-08-27 22:03 ` David Laight
2020-08-27 22:11 ` Joe Perches
2020-08-27 22:16 ` Kees Cook
2020-08-27 21:01 ` Denis Efremov
2020-08-27 21:36 ` Julia Lawall
2020-08-27 21:44 ` Joe Perches
2020-08-27 22:38 ` Denis Efremov
2020-08-27 22:48 ` Joe Perches
2020-08-27 22:20 ` Kees Cook
2020-08-27 22:45 ` Joe Perches
2020-08-28 4:12 ` Joe Perches
2020-08-28 7:58 ` Kees Cook
2020-08-28 8:10 ` Joe Perches
2020-08-28 8:22 ` Joe Perches
2020-08-28 7:39 ` David Laight
2020-08-27 21:54 ` David Laight
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