linux-kernel - Re: [PATCH] libfs: fix negative value support in simple_attr

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Message-ID: <YysiDKaLpiUUlX78@smile.fi.intel.com>
Date:   Wed, 21 Sep 2022 17:39:08 +0300
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Eliav Farber <farbere@...zon.com>, viro@...iv.linux.org.uk,
        yangyicong@...ilicon.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, hhhawa@...zon.com, jonnyc@...zon.com,
        Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [PATCH] libfs: fix negative value support in simple_attr_write()

On Mon, Sep 19, 2022 at 02:24:13PM -0700, Andrew Morton wrote:
> On Sun, 18 Sep 2022 13:50:36 +0000 Eliav Farber <farbere@...zon.com> wrote:
> 
> > After commit 488dac0c9237 ("libfs: fix error cast of negative value in
> > simple_attr_write()"), a user trying set a negative value will get a
> > '-EINVAL' error, because simple_attr_write() was modified to use
> > kstrtoull() which can handle only unsigned values, instead of
> > simple_strtoll().
> > 
> > This breaks all the places using DEFINE_DEBUGFS_ATTRIBUTE() with format
> > of a signed integer.
> > 
> > The u64 value which attr->set() receives is not an issue for negative
> > numbers.
> > The %lld and %llu in any case are for 64-bit value. Representing it as
> > unsigned simplifies the generic code, but it doesn't mean we can't keep
> > their signed value if we know that.
> > 
> > This change basically reverts the mentioned commit, but uses kstrtoll()
> > instead of simple_strtoll() which is obsolete.
> > 
> 
> https://lkml.kernel.org/r/20220919172418.45257-1-akinobu.mita@gmail.com
> addresses the same thing.
> 
> Should the final version of this fix be backported into -stable trees?

But it questioning the formatting string as a parameter. Why do we need that
in the first place then?

-- 
With Best Regards,
Andy Shevchenko