linux-kernel - Re: [PATCH v6 9/9] vsprintf: Avoid confusion between invalid address and value

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Date:   Wed, 20 Feb 2019 10:24:25 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 9/9] vsprintf: Avoid confusion between invalid address
 and value

On Tue 2019-02-19 13:06:17, Andy Shevchenko wrote:
> On Tue, Feb 19, 2019 at 5:07 AM Sergey Senozhatsky
> <sergey.senozhatsky.work@...il.com> wrote:
> 
> > Suppose, in my driver I want to sprintf() IPv4 address. The longest
> > possible address is 3 * 4 (%d%d%d) + 3 bytes (dots) + terminating NULL.
> > E.g. 111.111.111.111
> >
> > forcing sprintf() to write "(invalid address)" to a 16-bytes buffer,
> > but the thing is - strlen("(invalid address)") > 16.

Good catch!

> It would print as many characters as buffer allows. In your case above
> the use of sprintf() is a bit fragile.

Heh, I do not see it used anywhere in the code. Only "%pi6" is used
in a real code and always a safe way.

> But yes, the error messages should not be longer than 8 / 16 bytes
> depending on 32- or 64-bit build we have.

Well, better be on the safe side. I'll move it at the beginning
of the patchset.

Best Regards,
Petr

PS: I am a bit busy with some other things. I'll send v7 later.
I think that it is a material for 5.2. This patchset would deserve
some testing in linux-next and we are already too close to
the 5.1 merge window.