linux-kernel - Re: [PATCH] kernel/sysctl.c: If "count" including the terminating byte '\0' the write system call should retrun success.

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Message-ID: <87mvwsubz1.fsf@x220.int.ebiederm.org>
Date:	Fri, 11 Sep 2015 12:01:22 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Sean Fu <fxinrong@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Eric B Munson <emunson@...mai.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Don Zickus <dzickus@...hat.com>,
	Heinrich Schuchardt <xypron.glpk@....de>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/sysctl.c: If "count" including the terminating byte '\0' the write system call should retrun success.

Sean Fu <fxinrong@...il.com> writes:

>> Sounds like a reasonable compromise. Sean, can you make a patch that
>> only affects the one proc file (comment it well in the code), and have
>> it accept nothing past the '\0'. Even if someone passed in "1 \0 2", it
>> would only see "1 "
> The current code uses uniform handler (e.g. "proc_dointvec") for all
> same type proc file.
> So all integer type proc file are affected.

No.  I do not believe the proprietary binary application you are dealing
with writes to all proc files that use the proc_dointvec handler.

> In fact, The behavior of all integer type proc file should be changed.

Not at all.  The only files that we can possibly justify changing today
are the files where an actual regression is being observed.

Because quite frankly 5 years is way too long to wait to report a
regression.  By and large software is reasonable and treats proc
files as text files where '\0' is an invalid character.

Accepting a '\0' is not at all reasonable for a text interface.  The
application that does it is buggy.

Eric
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