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-QBuwieG3ymXstdLTewAOONPKorpQFD_5QqjJ2BkkLQb2-g@mail.gmail.com>
Date:	Mon, 24 Aug 2015 23:33:58 +0800
From:	Sean Fu <fxinrong@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	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 Mon, Aug 24, 2015 at 8:27 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
>
> On August 24, 2015 1:56:13 AM PDT, Sean Fu <fxinrong@...il.com> wrote:
>>when the input argument "count" including the terminating byte "\0",
>>The write system call return EINVAL on proc file.
>>But it return success on regular file.
>
> Nonsense.  It will write the '\0' to a regular file because it is just data.
>
> Integers in proc are more than data.
>
> So I see no justification for this change.
In fact, "write(fd, "1\0", 2)" on Integers proc file return success on
2.6 kernel. I already tested it on 2.6.6.60 kernel.

So, The latest behavior of "write(fd, "1\0", 2)" is different from old
kernel(2.6).
This maybe impact the compatibility of some user space program.
>
>
> Eric
>
>>E.g. Writting two bytes ("1\0") to
>>"/proc/sys/net/ipv4/conf/eth0/rp_filter".
>>write(fd, "1\0", 2) return EINVAL.
>>
>>Signed-off-by: Sean Fu <fxinrong@...il.com>
>>---
>> kernel/sysctl.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>>diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>>index 19b62b5..c2b0594 100644
>>--- a/kernel/sysctl.c
>>+++ b/kernel/sysctl.c
>>@@ -2004,7 +2004,7 @@ static int do_proc_dointvec_conv(bool *negp,
>>unsigned long *lvalp,
>>        return 0;
>> }
>>
>>-static const char proc_wspace_sep[] = { ' ', '\t', '\n' };
>>+static const char proc_wspace_sep[] = { ' ', '\t', '\n', '\0' };
>>
>> static int __do_proc_dointvec(void *tbl_data, struct ctl_table *table,
>>                  int write, void __user *buffer,
>
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