linux-kernel - Re: [PATCH 2/2] reboot: fix parsing of reboot cpu number

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Message-ID: <CAFnufp30qPaTgWSnoDkAGfwqhS+D7ov56M6g0u8jO0JQ4DPMXg@mail.gmail.com>
Date:   Fri, 16 Oct 2020 23:34:25 +0200
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Kees Cook <keescook@...omium.org>, Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Arnd Bergmann <arnd@...db.de>, Mike Rapoport <rppt@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Robin Holt <robinmholt@...il.com>,
        Fabian Frederick <fabf@...net.be>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] reboot: fix parsing of reboot cpu number

On Fri, Oct 16, 2020 at 9:26 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Fri, Oct 16, 2020 at 08:09:07PM +0200, Matteo Croce wrote:
> > From: Matteo Croce <mcroce@...rosoft.com>
> >
> > The kernel cmdline reboot= argument allows to specify the CPU used
> > for rebooting, with the syntax `s####` among the other flags, e.g.
> >
> >   reboot=soft,s4
> >   reboot=warm,s31,force
> >
> > In the early days the parsing was done with simple_strtoul(), later
> > deprecated in favor of the safer kstrtoint() which handles overflow.
> >
> > But kstrtoint() returns -EINVAL if there are non-digit characters
> > in a string, so if this flag is not the last given, it's silently
> > ignored as well as the subsequent ones.
> >
> > To fix it, revert the usage of simple_strtoul(), which is no longer
> > deprecated, and restore the old behaviour.
>
> It is? Is there a reference, because this was never updated:
> https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull
>
> --
> Kees Cook

Seems so, Petr Mladek replied to the previous patch:

> I suggest to go back to simple_strtoul(). It is not longer obsolete.
> It still exists because it is needed for exactly this purpose,
> see the comment in include/linux/kernel.h

The comment says:

/*
 * Use kstrto<foo> instead.
 *
 * NOTE: simple_strto<foo> does not check for the range overflow and,
 * depending on the input, may give interesting results.
 *
 * Use these functions if and only if you cannot use kstrto<foo>, because
 * the conversion ends on the first non-digit character, which may be far
 * beyond the supported range. It might be useful to parse the strings like
 * 10x50 or 12:21 without altering original string or temporary buffer in use.
 * Keep in mind above caveat.
 */

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/kernel.h?h=v5.9#n452

Cheers,
-- 
per aspera ad upstream