linux-kernel - Re: [PATCH v2 2/3] fpga manager: framework core

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Message-ID: <20141206140218.GB19672@amd>
Date:	Sat, 6 Dec 2014 15:02:18 +0100
From:	Pavel Machek <pavel@...x.de>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	atull@...nsource.altera.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Simek <monstr@...str.eu>,
	Michal Simek <michal.simek@...inx.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Rob Herring <robh+dt@...nel.org>,
	Ira Snyder <iws@...o.caltech.edu>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>, philip@...ister.org,
	rubini <rubini@...dd.com>,
	Steffen Trumtrar <s.trumtrar@...gutronix.de>,
	Jason <jason@...edaemon.net>, kyle.teske@...com,
	Nicolas Pitre <nico@...aro.org>,
	"Balbi, Felipe" <balbi@...com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	David Brown <davidb@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	David Miller <davem@...emloft.net>, cesarb@...arb.net,
	"sameo@...ux.intel.com" <sameo@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alan Tull <delicious.quinoa@...il.com>,
	dinguyen@...nsource.altera.com,
	Yves Vandervennet <yvanderv@...nsource.altera.com>
Subject: Re: [PATCH v2 2/3] fpga manager: framework core

On Sat 2014-12-06 13:00:17, Grant Likely wrote:
> On Fri, Oct 24, 2014 at 11:52 AM, Pavel Machek <pavel@...x.de> wrote:
> > Hi!
> >
> >> * /sys/class/fpga_manager/<fpga>/firmware
> >>   Name of FPGA image file to load using firmware class.
> >>   $ echo image.rbf > /sys/class/fpga_manager/<fpga>/firmware
> >
> > I .. still don't think this is good idea. What about namespaces?
> > The path corresponds to path in which namespace?
> 
> I don't understand your concern here. This allows userspace to name
> the FPGA bitstream that the kernel will use during request_firmware(),
> and it will show up as the $FIRMWARE value in the uevent file, but it
> is still the responsibility of userspace to choose what to load, and
> it can freely ignore the setting of $FIRMWARE if it needs to.

Well, consider chroot. I echo some filename but the file does not
exist for the userspace listening for the uevent.

> The process that actually loads the firmware into the kernel pretty
> much has to run in the normal linux environment. How do namespaces
> come into it? What exact problem do you see?

> > This shows why the interface is not right... Valid filename may
> > contain \n, right? It may even end with \n.
> 
> That's not an interface problem, it implementation problem. The
> function absolutely should scrub and validate it's input. It should
> also make sure that the string doesn't have any special characters so
> that /bin/sh doesn't barf on it (because the string will appear in the
> uevent file). I would check other users of request_firmware() to see
> if any of them allow userspace to specify the filename.

> That said, the other way to handle this is not to specify a valid
> filename through this interface at all. Just use a dummy placeholder
> name and expect userspace to load the correct file when the request is
> posted.

I'd go for that -- "dummy" works. Kernel is not a place to know shell
limitations for all possible shells.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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