linux-kernel - RE: [PATCH 1/1] Drivers: input: serio: New driver to support Hyper-V synthetic keyboard

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Date:	Mon, 16 Sep 2013 18:29:45 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Dan Carpenter <dan.carpenter@...cle.com>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vojtech@...e.cz" <vojtech@...e.cz>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: RE: [PATCH 1/1] Drivers: input: serio: New driver to support
 Hyper-V synthetic keyboard



> -----Original Message-----
> From: Dmitry Torokhov [mailto:dmitry.torokhov@...il.com]
> Sent: Monday, September 16, 2013 10:10 AM
> To: KY Srinivasan
> Cc: Dan Carpenter; olaf@...fle.de; gregkh@...uxfoundation.org;
> jasowang@...hat.com; linux-kernel@...r.kernel.org; vojtech@...e.cz; linux-
> input@...r.kernel.org; apw@...onical.com; devel@...uxdriverproject.org
> Subject: Re: [PATCH 1/1] Drivers: input: serio: New driver to support Hyper-V
> synthetic keyboard
> 
> On Mon, Sep 16, 2013 at 04:56:03PM +0000, KY Srinivasan wrote:
> >
> >
> > > -----Original Message-----
> > > From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> > > Sent: Monday, September 16, 2013 8:06 AM
> > > To: KY Srinivasan
> > > Cc: olaf@...fle.de; gregkh@...uxfoundation.org; jasowang@...hat.com;
> > > dmitry.torokhov@...il.com; linux-kernel@...r.kernel.org;
> vojtech@...e.cz;
> > > linux-input@...r.kernel.org; apw@...onical.com;
> devel@...uxdriverproject.org
> > > Subject: Re: [PATCH 1/1] Drivers: input: serio: New driver to support Hyper-V
> > > synthetic keyboard
> > >
> > > On Mon, Sep 16, 2013 at 02:46:24PM +0000, KY Srinivasan wrote:
> > > > > > +			case VM_PKT_DATA_INBAND:
> > > > > > +				hv_kbd_on_receive(device, desc);
> > > > >
> > > > > This is the error handling I mentioned at the top.  hv_kbd_on_receive()
> > > > > doesn't take into consideration the amount of data we recieved, it
> > > > > trusts the offset we recieved from the user.  There is an out of bounds
> > > > > read.
> > > >
> > > > What user are you referring to. The message is sent by the host - the user
> > > keystroke
> > > > is normalized into a fixed size packet by the host and sent to the  guest. We
> will
> > > parse this
> > > > packet, based on the host specified layout here.
> > > >
> > >
> > > The user means the hypervisor, yes.
> > >
> > > I don't want the hypervisor accessing outside of the buffer.  It is
> > > robustness issue.  Just check the offset against "bytes_recvd".  It's
> > > not complicated.
> >
> > At the outset, let me apologize for not understanding your concern.
> > You say: " I don't want the hypervisor accessing outside of the buffer"
> > Where did you see the hypervisor accessing anything outside the buffer?
> > The buffer is allocated by this driver and a packet from vmbus is read into this
> > buffer - this is the call to vmbus_recvpacket(). If the specified buffer is smaller
> > than the packet that needs to be read, then nothing will be read. Once the read
> > completes, we can be sure we have read a valid packet and can proceed to
> parse it in
> > this driver.
> 
> The concern is that number of bytes received and contents of a packet
> are not in sync. Imagine if we were told that 16 butes was received but
> in the packet offset is 78. Then we'll try reading well past the buffer
> boundary that we allocated for the packets.

I am not sure how this would be the case. Following are the semantics of the function
vmbus_recvpacket_raw():

If the packet to be read is larger than the buffer specified; nothing will be read and 
appropriate error is returned. If a  packet is read, the complete packet is read and 
so we can safely peek into this packet based on the information in the header.

Regards,


K. Y
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