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: <20150824125902.4ba11ec6@gandalf.local.home>
Date:	Mon, 24 Aug 2015 12:59:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Sean Fu <fxinrong@...il.com>
Cc:	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>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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, 24 Aug 2015 16:56:13 +0800
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.
> 
> E.g. Writting two bytes ("1\0") to "/proc/sys/net/ipv4/conf/eth0/rp_filter".
> write(fd, "1\0", 2) return EINVAL.

And what would do that? What tool broke because of this?

 echo 1 > /proc/sys/net/ipv4/conf/eth0/rp_filter

works just fine. strlen("string") would not include the nul character.
The only thing I could think of would be a sizeof(str), but then that
would include someone hardcoding an integer in a string, like:

	char val[] = "1"

	write(fd, val, sizeof(val));

Again, what tool does that?

If there is a tool out in the wild that use to work on 2.6 (and was
running on 2.6 then, and not something that was created after that
change), then we can consider this fix.

-- Steve
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