From patchwork Thu Dec 1 10:14:58 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Miklos Szeredi X-Patchwork-Id: 9455749 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id D1C9160515 for ; Thu, 1 Dec 2016 10:16:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C261A283BB for ; Thu, 1 Dec 2016 10:16:53 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B7506284CB; Thu, 1 Dec 2016 10:16:53 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6C3C4283BB for ; Thu, 1 Dec 2016 10:16:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752845AbcLAKQh (ORCPT ); Thu, 1 Dec 2016 05:16:37 -0500 Received: from mail-wj0-f170.google.com ([209.85.210.170]:33482 "EHLO mail-wj0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756100AbcLAKPL (ORCPT ); Thu, 1 Dec 2016 05:15:11 -0500 Received: by mail-wj0-f170.google.com with SMTP id xy5so199958963wjc.0 for ; Thu, 01 Dec 2016 02:15:10 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=I5PRItcm/0DvwNx8AKRWXXdnwbJDGy5tjeFHOYyyx1g=; b=miVn4v3iJ889KUn2owDX5iL08dR++2m6GfKxAI+UnhJN5D4BoGiWtUzfl+CCUliW6w Pcje06p8L4SlLGQ7qlLXA/+bxz2Yn/tv4r1TWtj/rEo2177i56HhP4sdu6g9xNZQSqwE hqoXx81tbI05l65DNxTd7Qit06gapPg1zdliotIdbum+vDpV3y+QffnjQ3oXr6Gcrd8+ lwkrc+JuVp2oGk93hnnQxoCJNOwuxjaWW4ulgAqevvEIPMM7ykZUbZFCmAdMxqcDDYQw LTarZT9Chsc6SGoxchOFmhS4KnOtWihDj0sbRBjsuK6c0FykvXb2/nFQcdPo9VVzopmL LuuA== X-Gm-Message-State: AKaTC03Ss6rFQhXwznYVYCXSxRlD7whpeJQhLFcD+XjLiJhrLJIoM1JyPsar2FarTZ0tb6nd X-Received: by 10.194.85.77 with SMTP id f13mr32899464wjz.187.1480587309962; Thu, 01 Dec 2016 02:15:09 -0800 (PST) Received: from veci.piliscsaba.szeredi.hu (pool-dsl-2c-0018.externet.hu. [217.173.44.24]) by smtp.gmail.com with ESMTPSA id ab10sm77218141wjc.45.2016.12.01.02.15.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Dec 2016 02:15:09 -0800 (PST) From: Miklos Szeredi To: Al Viro Cc: linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH 3/8] mm: ovl: copy-up on MAP_SHARED Date: Thu, 1 Dec 2016 11:14:58 +0100 Message-Id: <1480587303-25088-4-git-send-email-mszeredi@redhat.com> X-Mailer: git-send-email 2.5.5 In-Reply-To: <1480587303-25088-1-git-send-email-mszeredi@redhat.com> References: <1480587303-25088-1-git-send-email-mszeredi@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP A corner case of a corner case is when - file opened for O_RDONLY - which is then memory mapped SHARED - file opened for O_WRONLY - contents modified - contents read back though the shared mapping Unfortunately it looks very difficult to do anything about the established shared map after the file is copied up. Instead when a read-only file is mapped shared overlayfs copies up the file before actually doing the map. This may result in unnecessary copy-ups (but so may copy-up on open(O_RDWR) for exampe). We can revisit this later if it turns out to be a performance problem in real life. Signed-off-by: Miklos Szeredi --- mm/util.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/mm/util.c b/mm/util.c index 1a41553db866..449272271840 100644 --- a/mm/util.c +++ b/mm/util.c @@ -300,6 +300,28 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr, ret = security_mmap_file(file, prot, flag); if (!ret) { + /* + * Special treatment for overlayfs: + * + * Take MAP_SHARED/PROT_READ as hint about future writes to the + * file (through another file descriptor). Caller might not + * have had such an intent, but we hope MAP_PRIVATE will be used + * in most such cases. + * + * If we don't copy up now and the file is modified, it becomes + * really difficult to change the mapping to match that of the + * file's content later. + * + * Copy up needs to be done without mmap_sem since it takes vfs + * locks which would potentially deadlock under mmap_sem. + */ + if ((flag & MAP_SHARED) && !(prot & PROT_WRITE) && file) { + void *p = d_real(file->f_path.dentry, NULL, O_WRONLY); + + if (IS_ERR(p)) + return PTR_ERR(p); + } + if (down_write_killable(&mm->mmap_sem)) return -EINTR; ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff,