Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t

From: ebiederm@xmission.com (Eric W. Biederman)
To: Sebastian Capella <sebastian.capella@linaro.org>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linaro-kernel@lists.linaro.org, patches@linaro.org,
	"Serge Hallyn" <serge.hallyn@canonical.com>,
	"Stephen Warren" <swarren@nvidia.com>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t
Date: Thu, 10 Oct 2013 15:47:45 -0700	[thread overview]
Message-ID: <878uy0u4j2.fsf@tw-ebiederman.twitter.com> (raw)
In-Reply-To: <20131010175010.17870.58060@capellas-linux> (Sebastian Capella's message of "Thu, 10 Oct 2013 10:50:10 -0700")

Sebastian Capella <sebastian.capella@linaro.org> writes:

> Quoting Sebastian Capella (2013-10-03 16:47:35)
>> Quoting Sebastian Capella (2013-10-03 14:42:46)
>> > Quoting Andrew Morton (2013-10-03 14:15:23)
>> > > On Thu,  3 Oct 2013 14:10:37 -0700 Sebastian Capella <sebastian.capella@linaro.org> wrote:
>> > > 
>> > > > Enhance name_to_dev_t to handle trailing newline characters
>> > > > on device paths.  Some inputs to name_to_dev_t may come from
>> > > > userspace where oftentimes a '\n' is appended to the path.
>> > > > Added const to the name buffer in both the function
>> > > > declaration and the prototype to reflect input buffer
>> > > > handling.
>> > > > 
>> > > > By handling trailing newlines in name_to_dev_t, userspace
>> > > > buffers may be directly passed to name_to_dev_t without
>> > > > modification.
>> > > 
>> > > We have lib/string.c:strim() - perhaps this patch would be
>> > > neater if it were to use it?
>> > 
>> > Hi Morton,
>> > 
>> > I was intending to respect the const handling of the input buffer.
>> > 
>> > The actual buffer in this case is not really const as it comes from
>> > the file buffering, but removing the const requires changing the
>> > store function defined in the kobj_attribute, and would propagate
>> > to many areas in the kernel.
>> > 
>> > Modifying the buffer and removing the const was also suggested by Pavel.
>> > After some discussion I posted this version which did not change the
>> > buffer or the prototype.
>> > 
>> > Please let me know if the preference is to modify the store function
>> > definition.
>> > 
>> > I'll prepare a patchset that removes the consts to see how much is
>> > changed.
>> > 
>> > Thanks,
>> > 
>> > Sebastian
>> 
>> Hi Andrew,
>> 
>> Sorry for calling you Morton earlier.
>> 
>> I looked into removing the const from the store function, but I'm not sure
>> this is the right idea, so I'm going to shelf that for now.
>> 
>> Please let me know your thoughts.
>> 
>> Thanks,
>> 
>> Sebastian
>  
> Ping...
>
> Hi Andrew,
>
> Do you have any feedback on this?
>
> Below are the three options considered thus far.  Do
> you have any additional suggestions or preferences?

What is wrong with requiring userspace to use echo -n ?

That by far seems the simplest and least error prone solution.

Eric