Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933434AbbLGWm2 (ORCPT ); Mon, 7 Dec 2015 17:42:28 -0500 Received: from mail-io0-f172.google.com ([209.85.223.172]:34080 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933048AbbLGWmW convert rfc822-to-8bit (ORCPT ); Mon, 7 Dec 2015 17:42:22 -0500 MIME-Version: 1.0 In-Reply-To: References: <20151203000342.GA30015@www.outflux.net> Date: Mon, 7 Dec 2015 14:42:22 -0800 X-Google-Sender-Auth: gKsTRi_ndCNb4hEDRif0A5o77mo Message-ID: Subject: Re: [PATCH v2] clear file privilege bits when mmap writing From: Kees Cook To: yalin wang 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 , LKML Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1396 Lines: 35 On Thu, Dec 3, 2015 at 5:45 PM, yalin wang wrote: > >> 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 . Yes, good point. This needs to be added. I will send a new patch. Thanks! -Kees -- Kees Cook Chrome OS & Brillo Security -- 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/