Re: [RESEND v4 2/6] remoteproc: debugfs: Add ability to boot remote processor using debugfs

From: Arnd Bergmann <arnd@arndb.de>
To: linux-arm-kernel@lists.infradead.org
Cc: Lee Jones <lee.jones@linaro.org>, Bjorn Andersson <bjorn@kryo.se>,
	Ohad Ben-Cohen <ohad@wizery.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Florian Fainelli <f.fainelli@gmail.com>,
	kernel@stlinux.com, Nathan_Lynch@mentor.com,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	ludovic.barre@st.com, Maxime Coquelin <maxime.coquelin@st.com>
Subject: Re: [RESEND v4 2/6] remoteproc: debugfs: Add ability to boot remote processor using debugfs
Date: Thu, 03 Dec 2015 13:49:09 +0100	[thread overview]
Message-ID: <5329827.I5W30K072M@wuerfel> (raw)
In-Reply-To: <20151203122634.GX12874@x1>

On Thursday 03 December 2015 12:26:34 Lee Jones wrote:
> > >
> > > +static ssize_t rproc_state_write(struct file *filp, const char __user *userbuf,
> > > +                                size_t count, loff_t *ppos)
> > > +{
> > > +       struct rproc *rproc = filp->private_data;
> > > +       char buf[10];
> > > +       int ret;
> > > +
> > > +       if (count > sizeof(buf))
> > > +               return count;
> > > +       ret = copy_from_user(buf, userbuf, count);
> > > +       if (ret)
> > > +               return -EFAULT;
> > > +
> > > +       if (buf[count - 1] == '\n')
> > > +               buf[count - 1] = '\0';
> > 
> > I believe you can get here with count = 0.
> 
> I'm pretty sure you can't.
> 
> If you are sure that you can, if you can provide me with a way of
> testing, I'd be happy to put in provisions.
> 

I think that a zero-length write() from user space ends up in the write
file operation.

Also, we get a gcc warning about the out-of-bounds access for code like
this, and checking that count is larger than zero avoids the warning.

	Arnd