linux-kernel - Re: [PATCH -next 2/3] xen: balloon: Replaced simple

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Date:   Thu, 27 May 2021 17:37:30 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "'Chen Huang'" <chenhuang5@...wei.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Mark Fasheh <mark@...heh.com>,
        Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Jens Axboe <axboe@...nel.dk>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>
Subject: Re: [PATCH -next 2/3] xen: balloon: Replaced simple_strtoull() with
 kstrtoull()

On Thu, May 27, 2021 at 02:10:21PM +0000, David Laight wrote:
> From: Chen Huang
> > Sent: 26 May 2021 10:20
> > 
> > The simple_strtoull() function is deprecated in some situation, since
> > it does not check for the range overflow, use kstrtoull() instead.
> > 
> ...
> > -	target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
> > +	ret = kstrtoull(buf, 0, &target_bytes);
> > +	if (ret)
> > +		return ret;
> > +	target_bytes *= 1024;
> 
> I'd have thought it was more important to check *endchar
> than overflow.

That's one of the differences between simple_strtoull() and kstrtoull().
The simple_strtoull() will accept a string like "123ABC", but kstrtoull()
will only accept NUL terminated numbers or a newline followed by a NUL
terminator.  Which is fine in this context because users will be doing
"echo 1234 > /sys/foo".

> If you are worried about overflow you need a range check
> before the multiply.

This is probably a case where if the users cause an integer overflow
then they get what they deserve.

regards,
dan carpenter