From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751004AbWEEUic (ORCPT ); Fri, 5 May 2006 16:38:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751767AbWEEUic (ORCPT ); Fri, 5 May 2006 16:38:32 -0400 Received: from cantor.suse.de ([195.135.220.2]:8100 "EHLO mx1.suse.de") by vger.kernel.org with ESMTP id S1751004AbWEEUib (ORCPT ); Fri, 5 May 2006 16:38:31 -0400 From: Andi Kleen To: Alexey Toptygin Subject: Re: [PATCH] sendfile compat functions on x86_64 and ia64 Date: Fri, 5 May 2006 22:38:26 +0200 User-Agent: KMail/1.9.1 Cc: linux-kernel@vger.kernel.org, tony.luck@intel.com References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200605052238.26834.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Friday 05 May 2006 02:45, Alexey Toptygin wrote: > > Hi, > > I'm a kernel noob, so I apologise in advance if I completely misunderstood > something. In arch/x86_64/ia32/sys_ia32.c there is this code: > > sys32_sendfile(int out_fd, int in_fd, compat_off_t __user *offset, s32 count) > [snip] > ret = sys_sendfile(out_fd, in_fd, offset ? &of : NULL, count); > > However on ia32, count (a size_t) is u32. I think this is taking the u32 > value from the 32 bit userland, sign-extending it to 64 bits, then giving > it to sys_sendfile in a u64. So, a count >= 1<<31 passed from the 32 bit > app will become a count >= ((1<<33)-1)<<31 given to sys_sendfile. > > Now, I don't think this actually hurts anything, because sys_sendfile > passes a max of ((1<<31)-1) to do_sendfile, plus rw_verify_area will > reject values that are negative when cast to ssize_t; but, this is > certainly confusing. With your change there wouldn't be any sign extension and rw_verify_area couldn't reject negative values them anymore. I think it would be a wrong change because it would differ from a native 32bit kernel. -Andi