Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754402Ab2K2Bp2 (ORCPT ); Wed, 28 Nov 2012 20:45:28 -0500 Received: from mail-da0-f46.google.com ([209.85.210.46]:54309 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752564Ab2K2Bp1 (ORCPT ); Wed, 28 Nov 2012 20:45:27 -0500 Message-ID: <50B6BE34.2010109@vflare.org> Date: Wed, 28 Nov 2012 17:45:24 -0800 From: Nitin Gupta User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Minchan Kim CC: Greg KH , Seth Jennings , Dan Carpenter , Sam Hansen , Tomas M , Mihail Kasadjikov , Linux Driver Project , linux-kernel Subject: Re: [PATCH] zram: Prevent use of unmapped buffer References: <1354001167-24878-1-git-send-email-ngupta@vflare.org> <20121128051505.GD23136@blaptop> <20121129013320.GA24077@blaptop> In-Reply-To: <20121129013320.GA24077@blaptop> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2333 Lines: 60 On 11/28/2012 05:33 PM, Minchan Kim wrote: > On Wed, Nov 28, 2012 at 02:15:05PM +0900, Minchan Kim wrote: >> Hi Nitin, >> >> On Mon, Nov 26, 2012 at 11:26:07PM -0800, Nitin Gupta wrote: >>> The commit c8f2f0db1 ("zram: Fix handling of incompressible pages") >>> introduced a bug which caused a kunmap()'ed buffer to be used in case >> I got confused by the descripton. :( >> The descripton is not right. >> The problem is to access freed memory, not accessing to kunmaped buffer. >> >> partial I/O write. >> >> 1. uncmem = kmalloc >> 2. zram_decompress_page(uncmem) >> 3. memcpy(uncmem, user_mem) >> 4. lzo1x_1_compress(uncmem) >> 5. kfree(uncmem) >> 6. src = uncmem >> 7. memcpy(cmem, src, clen) <----- HIT >> >>> of partial writes where the data was found to be incompressible. >>> > I got it. You shouldn't mention partial write for proper description > because it was usecase for swap-over-zram so it can't make partial write. > Without partial write mention, your description is right but the problem > I mentioned above is another problem for partial write so we need a another > patch. I will cook. I will include explanation of both the cases: use of unmapped buffer and freed buffer, when I resend these patches. > >>> This fixes bug 50081: >>> https://bugzilla.kernel.org/show_bug.cgi?id=50081 >>> >>> Signed-off-by: Nitin Gupta >>> Reported-by: Mihail Kasadjikov >>> Reported-by: Tomas M >> Good catch! Shame on me. I should have reivewed more carefully. :( >> Please resend it with revised descrption and title. >> I will rebase mh patchset just sent on top of this bug fix patch. >> >> P.S) Sigh, Now code isn't clean due to partial read/write path handling. >> IMHO, sooner or later, we need refactoring. >> >> -- >> Kind regards, >> Minchan Kim >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/