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

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Date:   Thu, 15 Jun 2023 11:38:13 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>
CC:     'Demi Marie Obenour' <demi@...isiblethingslab.com>,
        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

From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Sent: 15 June 2023 12:24
> ...
> 
> > > > What sort of formats and data are being used?
> > >
> > > Base-10 or base-16 integers, with whitespace never being valid.
> >
> > In which case sscanf() really isn't what you are looking for.
> >
> > > > 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.
> >
> > They are not 'broken', that is what is useful most of the time.
> > The usual problem is that "020" is treated as octal.
> >
> > > I’m trying to replace their uses in Xen with custom parsing code.
> >
> > Then write a custom parser :-)
> 
> Hmm... Usually we are against zillion implementations of the same with zillion
> bugs hidden (each buggy implementation with its own bugs).

Using strtoull() for the actual numeric conversion removes most of that.

I am intrigued about why you want to error leading whitespace.
I bet you'll find something that is passing space-padded input.
It might be against the letter of the spec - but it doesn't mean
it doesn't happen.

	David

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