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: <CAGk-QBtmbkVukWO-kSxUEj_nyZHnxho-RfHRoH_PgcPRdmZxDA@mail.gmail.com>
Date:	Fri, 28 Aug 2015 11:31:54 +0800
From:	Sean Fu <fxinrong@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.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>,
	Andrew Morton <akpm@...ux-foundation.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.

On Thu, Aug 27, 2015 at 4:32 PM, Sean Fu <fxinrong@...il.com> wrote:
> On Thu, Aug 27, 2015 at 10:32 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>> On Thu, 27 Aug 2015 08:17:29 +0800
>> Sean Fu <fxinrong@...il.com> wrote:
>>
>>> On Thu, Aug 27, 2015 at 4:36 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>>> > On Wed, 26 Aug 2015 23:48:01 +0800
>>> > Sean Fu <fxinrong@...il.com> wrote:
>>> >
>>> >
>>> >> > Defending the patch, I can't imagine any user space code expecting the
>>> >> > current behavior. The current behavior is that if you write "1\0" it
>>> >> > will error out instead of accepting the "1". I can't come up with a
>>> >> > scenario that would require userspace to expect "1\0" to fail. Can you?
>>> >> Thanks
>>> >
>>> > Although, with the current patch, would "1\02" fail? It should.
>>> Yes, "1\02" is equal to "1\2"(count=2) or "1\2\0"(count=3), So it should fail.
>>
>> Sorry, I meant "1\0 2"
> In this case, The patch behavior is accepting the "1" and discarding
> other bytes.
> for (; left && vleft--; i++, first=0) {    //vleft is 1 for integer
> type or unsigned long type proc file
>
>>
>> -- Steve
>>
>>>
>>> code
>>> len = write(fd, "1\0\2", 3);
>>>
>>> strace execute result:
>>> write(3, "1\2\0", 3)                    = -1 EINVAL (Invalid argument)
If vleft > 1, "1\0 2" is treated as invalid paraments and all string
include '\0' will be invalid.

>>>
>>> >
>>> > -- Steve
>>
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