linux-kernel - Re: [PATCH] usb: fix potential integer overflow in usb_sg

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Date:	Tue, 19 Jan 2016 09:57:15 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Insu Yun <wuninsu@...il.com>
cc:	gregkh@...uxfoundation.org, <stefan.koch10@...il.com>,
	Kris Borer <kborer@...il.com>, <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Taesoo Kim <taesoo@...ech.edu>,
	Yeongjin Jang <yeongjin.jang@...ech.edu>,
	"Yun, Insu" <insu@...ech.edu>, Changwoo Min <changwoo@...ech.edu>
Subject: Re: [PATCH] usb: fix potential integer overflow in usb_sg_init

On Mon, 18 Jan 2016, Insu Yun wrote:

> On Mon, Jan 18, 2016 at 1:32 PM, Alan Stern <stern@...land.harvard.edu>
> wrote:
> 
> > On Mon, 18 Jan 2016, Insu Yun wrote:
> >
> > > If nents value is sufficient large, e.g 0x40000000,
> > > then it can overflow size in kmalloc and heap overflow happesns.
> > > Therefore nents value needs to be checked to prevent overflow.
> >
> > I don't see why.  You seem to be assuming that failure with -EINVAL is
> > better than failure with a heap overflow.  I disagree; a heap overflow
> > provides more debugging information to help locate the reason for the
> > underlying problem.
> >
> 
> I agree that heap overflow gives more information than -EINVAL.
> However, I think -EINVAL already gives sufficient information for debugging.

Actually it doesn't.  -EINVAL return codes occur all over the place.  
It's not easy to tell exactly what went wrong when one of them pops up.

> And I thin crash is bad, so returning -EINVAL seems better.

A better solution in this case would be to avoid overflows by changing 
the kmalloc call to kmalloc_array, instead of duplicating the code.

Alan Stern