linux-kernel - Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev

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Message-Id: <20140129104106.793524a07e48324a32dc6f06@linux-foundation.org>
Date:	Wed, 29 Jan 2014 10:41:06 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sebastian Capella <sebastian.capella@...aro.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Pavel Machek" <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	"Serge Hallyn" <serge.hallyn@...onical.com>,
	"Stephen Warren" <swarren@...dia.com>,
	"Jens Axboe" <axboe@...nel.dk>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Al Viro" <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in
 name_to_dev_t

On Wed, 29 Jan 2014 10:29:56 -0800 Sebastian Capella <sebastian.capella@...aro.org> wrote:

> Hi Andrew,
> 
> By the way, I do see a call (sysfs_streq) in use for this purpose
> other places.  Sorry, I didn't find it while looking at the original
> problem.  I'm not sure if this is preferable, but it appears to have
> been added specifically for the strings coming through sysfs.

Yes, I wrote it ;)

I didn't think sysfs_streq() is well suited to this problem.  And the
issue of possibly-null-terminated-strings coming in from userspace is a
common one, so it is desirable that we build up the suite of utilities
to handle this.

There are probably quite a lot of open-coded \n trimming loops which
can be cleaned up using such tools.

	grep -r "if .* == '\\\n'" .

> My preference is copying the string and cleaning it up before passing
> it to internal functions, even though we incur an allocation.

Yes.  Here on the kernel/userspace boundary we are typically running in
GFP_KERNEL context and the code is not performance critical - it is a
good fit.

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