linux-kernel - Re: [PATCH v3 0/4] Make sscanf() stricter

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Date:   Wed, 14 Jun 2023 16:08:51 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     David Laight <David.Laight@...lab.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Hans de Goede <hdegoede@...hat.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Lee Jones <lee@...nel.org>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v3 0/4] Make sscanf() stricter

On Wed, Jun 14, 2023 at 08:23:56AM +0000, David Laight wrote:
> From: Demi Marie Obenour
> > Sent: 13 June 2023 16:35
> > 
> > On Tue, Jun 13, 2023 at 01:02:59PM +0000, David Laight wrote:
> > > From: Demi Marie Obenour
> > > > Sent: 12 June 2023 22:23
> > > ....
> > > > sscanf(), except to the extent that -Werror=format can keep working.
> > > > Userspace sscanf() is almost useless: it has undefined behavior on
> > > > integer overflow and swallows spaces that should usually be rejected.
> > >
> > > scanf() is designed for parsing space separated data.
> > > Eating spaces it part of its job description.
> > >
> > > 	David
> > 
> > In this case I would prefer to have two versions: one that eats spaces
> > and one that does not.  For instance, I don’t think any user of
> > xenbus_scanf() wants the space-swallowing behavior.  This can be worked
> > around in xenbus_scanf(), of course, by having it reject strings with
> > spaces (as determened by isspace()) before calling vsscanf().
> 
> What sort of formats and data are being used?

Base-10 or base-16 integers, with whitespace never being valid.

> The "%s" format terminates on whitespace.
> Even stroul() (and friends) will skip leading whitespace.

Yes, which is a reason that strto*l() are just broken IMO.  I’m trying
to replace their uses in Xen with custom parsing code.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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