linux-kernel - Re: [PATCH v3 1/2] kernel.h: Update comment about simple

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Message-ID: <20190708134806.crpgmv3zzhd4nz3h@pathway.suse.cz>
Date:   Mon, 8 Jul 2019 15:48:06 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mans Rullgard <mans@...sr.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] kernel.h: Update comment about
 simple_strto<foo>() functions

On Mon 2019-07-08 15:13:50, Geert Uytterhoeven wrote:
> Hi Petr,
> 
> On Mon, Jul 8, 2019 at 3:02 PM Petr Mladek <pmladek@...e.com> wrote:
> > On Thu 2019-07-04 14:55:31, Andy Shevchenko wrote:
> > > There were discussions in the past about use cases for
> > > simple_strto<foo>() functions and, in some rare cases,
> > > they have a benefit over kstrto<foo>() ones.
> > >
> > > Update a comment to reduce confusion about special use cases.
> > >
> > > Suggested-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
> > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > ---
> > > - update comment based on Geert's input
> > >  include/linux/kernel.h | 17 ++++++++++++-----
> > >  1 file changed, 12 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > > index 0c9bc231107f..63663c44933d 100644
> > > --- a/include/linux/kernel.h
> > > +++ b/include/linux/kernel.h
> > > @@ -332,8 +332,7 @@ int __must_check kstrtoll(const char *s, unsigned int base, long long *res);
> > >   * @res: Where to write the result of the conversion on success.
> > >   *
> > >   * Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
> > > - * Used as a replacement for the obsolete simple_strtoull. Return code must
> > > - * be checked.
> > > + * Used as a replacement for the simple_strtoull. Return code must be checked.
> > >  */
> > >  static inline int __must_check kstrtoul(const char *s, unsigned int base, unsigned long *res)
> > >  {
> > > @@ -361,8 +360,7 @@ static inline int __must_check kstrtoul(const char *s, unsigned int base, unsign
> > >   * @res: Where to write the result of the conversion on success.
> > >   *
> > >   * Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
> > > - * Used as a replacement for the obsolete simple_strtoull. Return code must
> > > - * be checked.
> > > + * Used as a replacement for the simple_strtoull. Return code must be checked.
> > >   */
> > >  static inline int __must_check kstrtol(const char *s, unsigned int base, long *res)
> > >  {
> > > @@ -438,7 +436,16 @@ static inline int __must_check kstrtos32_from_user(const char __user *s, size_t
> > >       return kstrtoint_from_user(s, count, base, res);
> > >  }
> > >
> > > -/* Obsolete, do not use.  Use kstrto<foo> instead */
> > > +/*
> > > + * Use kstrto<foo> instead.
> > > + *
> > > + * NOTE: The simple_strto<foo> does not check for overflow and,
> > > + *    depending on the input, may give interesting results.
> >
> > I am a bit confused whether the interesting results are caused
> > by the buffer overflow or if there is another reason.
> 
> Which buffer overflow?
> > If it is because of the overflow, I would remove the 2nd line. I guess
> > that anyone knows what a buffer overflow might cause.
> 
> AFAIK, the overflow is a numerical overflow.
> 
> The "interesting result" is that the function keeps parsing until it finds
> a character that doesn't fit in the range of expected characters, according
> to the specified numerical base, but further ignoring character class.
> But that's really what you want, when you want to parse things like
> 10x50 or 10:50.

Thanks for the detailed explanation. It means that the new text is
still confusing. Please, make it more explicit, e.g.

NOTE: simple_strto<foo> does not check for the range overflow.

      The conversion ends on the first non-number character. It is
      needed only for parsing strings like 10;50; or 10:50 without
      the need to modify the original string.

      Be aware that the number base is being detected. Therefore, for
      example, "0x1a" returns 26 (base 16) and "019" returns 1 (base 8).

Best Regards,
Petr