Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754650AbbLDBpL (ORCPT ); Thu, 3 Dec 2015 20:45:11 -0500 Received: from mail-pa0-f51.google.com ([209.85.220.51]:35522 "EHLO mail-pa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753366AbbLDBpJ convert rfc822-to-8bit (ORCPT ); Thu, 3 Dec 2015 20:45:09 -0500 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.0 \(3094\)) Subject: Re: [PATCH v2] clear file privilege bits when mmap writing From: yalin wang In-Reply-To: <20151203000342.GA30015@www.outflux.net> Date: Thu, 3 Dec 2015 17:45:06 -0800 Cc: Andrew Morton , Jan Kara , Willy Tarreau , "Eric W. Biederman" , "Kirill A. Shutemov" , Oleg Nesterov , Rik van Riel , Chen Gang , Davidlohr Bueso , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: References: <20151203000342.GA30015@www.outflux.net> To: Kees Cook X-Mailer: Apple Mail (2.3094) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1183 Lines: 29 > On Dec 2, 2015, at 16:03, Kees Cook wrote: > > Normally, when a user can modify a file that has setuid or setgid bits, > those bits are cleared when they are not the file owner or a member > of the group. This is enforced when using write and truncate but not > when writing to a shared mmap on the file. This could allow the file > writer to gain privileges by changing a binary without losing the > setuid/setgid/caps bits. > > Changing the bits requires holding inode->i_mutex, so it cannot be done > during the page fault (due to mmap_sem being held during the fault). > Instead, clear the bits if PROT_WRITE is being used at mmap time. > > Signed-off-by: Kees Cook > Cc: stable@vger.kernel.org > — is this means mprotect() sys call also need add this check? mprotect() can change to PROT_WRITE, then it can write to a read only map again , also a secure hole here . Thanks -- 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/