Re: [Ocfs2-devel] [PATCH -next 2/3] xen: balloon: Replaced simple_strtoull() with kstrtoull()

From: Dan Carpenter <dan.carpenter@oracle.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Yang Yingliang <yangyingliang@huawei.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Nathan Lynch <nathanl@linux.ibm.com>,
	Jens Axboe <axboe@kernel.dk>,
	Andrew Donnellan <ajd@linux.ibm.com>,
	'Chen Huang' <chenhuang5@huawei.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	"ocfs2-devel@oss.oracle.com" <ocfs2-devel@oss.oracle.com>
Subject: Re: [Ocfs2-devel] [PATCH -next 2/3] xen: balloon: Replaced simple_strtoull() with kstrtoull()
Date: Thu, 27 May 2021 17:37:30 +0300	[thread overview]
Message-ID: <20210527143729.GL24442@kadam> (raw)
In-Reply-To: <0f03f9b9ff41460db2935e077f7f80c7@AcuMS.aculab.com>

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

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