From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752667AbaHTQ4l (ORCPT ); Wed, 20 Aug 2014 12:56:41 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:58138 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751802AbaHTQ4i (ORCPT ); Wed, 20 Aug 2014 12:56:38 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: "Eric W. Biederman" , Luis Henriques Subject: [PATCH 3.11 139/141] mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount Date: Wed, 20 Aug 2014 17:56:30 +0100 Message-Id: <1408553792-25134-2-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1408354398-10226-1-git-send-email-luis.henriques@canonical.com> References: <1408354398-10226-1-git-send-email-luis.henriques@canonical.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Eric W. Biederman" commit 07b645589dcda8b7a5249e096fece2a67556f0f4 upstream. There are no races as locked mount flags are guaranteed to never change. Moving the test into do_remount makes it more visible, and ensures all filesystem remounts pass the MNT_LOCK_READONLY permission check. This second case is not an issue today as filesystem remounts are guarded by capable(CAP_DAC_ADMIN) and thus will always fail in less privileged mount namespaces, but it could become an issue in the future. Acked-by: Serge E. Hallyn Signed-off-by: "Eric W. Biederman" Signed-off-by: Luis Henriques --- fs/namespace.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index c98baa23e4d8..343158cb021c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1764,9 +1764,6 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags) if (readonly_request == __mnt_is_readonly(mnt)) return 0; - if (mnt->mnt_flags & MNT_LOCK_READONLY) - return -EPERM; - if (readonly_request) error = mnt_make_readonly(real_mount(mnt)); else @@ -1792,6 +1789,16 @@ static int do_remount(struct path *path, int flags, int mnt_flags, if (path->dentry != path->mnt->mnt_root) return -EINVAL; + /* Don't allow changing of locked mnt flags. + * + * No locks need to be held here while testing the various + * MNT_LOCK flags because those flags can never be cleared + * once they are set. + */ + if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) && + !(mnt_flags & MNT_READONLY)) { + return -EPERM; + } err = security_sb_remount(sb, data); if (err) return err; -- 1.9.1