Re: + lib-stringc-strlcpy-might-read-too-far.patch added to -mm tree

From: Dan Carpenter <dan.carpenter@oracle.com>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
	Vegard Nossum <vegard.nossum@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: + lib-stringc-strlcpy-might-read-too-far.patch added to -mm tree
Date: Tue, 15 Apr 2014 14:18:00 +0300	[thread overview]
Message-ID: <20140415111800.GW4963@mwanda> (raw)
In-Reply-To: <CACVxJT-f+K_z-XxqjDVU_QK-VJPqnCEbWuMJF1fyTL0V0xiTgA@mail.gmail.com>

On Tue, Apr 15, 2014 at 01:49:38PM +0300, Alexey Dobriyan wrote:
> Return value matters. It may not matter for kernel, because kernel is
> not heavy string user.
> But it is better to not diverge from master code:
> http://www.openbsd.org/cgi-bin/cvsweb/src/lib/libc/string/strlcpy.c?rev=1.11
> 

Oh...  Hm.  Maybe we should drop this patch then.

> Counter-rationale:
> * strlcpy() accepts strings, so if you're giving raw buffer you're
> doing it wrong.
> * last byte of last page argument is bogus because kernel copies data
> from userspace first.

The last byte of the page argument seems possible:

	foo = kmalloc();
	copy_from_user(foo, arg, sizeof(foo));
	strlcpy(dest.str, foo->bar, sizeof(dest.str));

It's a very unlikely scenario.  You have to be very unlucky to hit it at
all.

regards,
dan carpenter