linux-kernel - Re: [PATCH 06/14] lib/vsprintf.c: warn about too large precisions and field widths

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Message-ID: <87610oeaav.fsf@rasmusvillemoes.dk>
Date:	Thu, 26 Nov 2015 22:10:48 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/14] lib/vsprintf.c: warn about too large precisions and field widths

On Mon, Nov 23 2015, Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Mon, Nov 23, 2015 at 11:29 PM, Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>> The field width is overloaded to pass some extra information for
>> some %p extensions (e.g. #bits for %pb). But we might silently
>> truncate the passed value when we stash it in struct printf_spec (see
>> e.g. "lib/vsprintf.c: expand field_width to 24 bits").  Hopefully 23
>> value bits should now be enough for everybody, but if not, let's make
>> some noise.
>>
>> Do the same for the precision. In both cases, clamping seems more
>> sensible than truncating. While, according to POSIX, "A negative
>> precision is taken as if the precision were omitted.", the kernel's
>> printf has always treated that case as if the precision was 0, so we
>> use that as lower bound. For the field width, the smallest
>> representable value is actually -(1<<23), but a negative field width
>> means 'set the LEFT flag and use the absolute value', so we want the
>> absolute value to fit.
>>
>
> Do we need to do the same for bstr_printf() ?
>

Heh, apparently I didn't learn anything from 762abb51. Thanks, will fix
in next spin.

Rasmus
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