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

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Date:	Mon, 08 Dec 2014 14:53:39 -0600
From:	Rob Landley <rob@...dley.net>
To:	Grant Likely <grant.likely@...aro.org>,
	Pavel Machek <pavel@...x.de>
CC:	atull <atull@...nsource.altera.com>,
	Pantelis Antoniou <pantelis.antoniou@...sulko.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 <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	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>, Felipe Balbi <balbi@...com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	David Brown <davidb@...eaurora.org>,
	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 12/08/2014 11:50 AM, Grant Likely wrote:
> On Sat, 6 Dec 2014 14:55:33 +0100
> , Pavel Machek <pavel@...x.de>
>  wrote:
>> Hi!
>>
>>>> I am accustomed to doing 'echo -n' for most of sysfs anyway.  Once in a
>>>> while I am a bonehead and forget the '-n' and spend a few minutes
>>>> wondering why this thing that worked last week suddenly rejects all
>>>> commands.  I'm just trying to make my user interface a bit user-friendly.
>>>>
>>>> I will take out the '\n' stripping and update the documentation.  I didn't
>>>> realize this would be controversial.
>>>
>>> Don't. You're doing the right thing by scrubbing your input. Requiring
>>> 'echo -n' is just stupid when it is so easy to make work easily.
>>
>> 'foo\nbar\n' is unusual but valid filename in linux. It is bad idea to
>> echo filenames into files in the first place... and arbitrarily
>> disallowing certain filenames is not helping.
> 
> Meh. Just because it is a valid linux filename doesn't mean this
> interface is forced to accept it. There should be tighter rules about
> how the filename can be constructed. Allowing any arbitrary path for any
> arbitrary valid linux filename makes for a large attack surface.

"echo /bin/mdev > /proc/sys/kernel/hotplug" has worked fine, without the
-n, for most of a decade now. Requiring -n on echo would be weird.

I note that the filenames in /proc/mounts have an escape syntax for
arbitrary embedded weirdness. (To see it in action, mount a path with a
space in it.) If you really want to support that, there's presumably
code that can be genericized and reappropriated so you can escape a
newline you want to keep. But if your input has a normal unescaped
trailing newline, it _should_ be ignored.

Rob
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