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

[Rob Landley <rob@landley.net>]

On 12/08/2014 11:50 AM, Grant Likely wrote:
> On Sat, 6 Dec 2014 14:55:33 +0100
> , Pavel Machek <pavel@denx.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