From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753246AbaHTLuK (ORCPT ); Wed, 20 Aug 2014 07:50:10 -0400 Received: from ip4-83-240-18-248.cust.nbox.cz ([83.240.18.248]:59029 "EHLO ip4-83-240-18-248.cust.nbox.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752622AbaHTLoL (ORCPT ); Wed, 20 Aug 2014 07:44:11 -0400 From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "Eric W. Biederman" , Jiri Slaby Subject: [PATCH 3.12 064/104] mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount Date: Wed, 20 Aug 2014 13:43:27 +0200 Message-Id: X-Mailer: git-send-email 2.0.4 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Eric W. Biederman" 3.12-stable review patch. If anyone has any objections, please let me know. =============== 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. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn Signed-off-by: "Eric W. Biederman" Signed-off-by: Jiri Slaby --- fs/namespace.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 34fa7a52f373..8e90b037b706 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1806,9 +1806,6 @@ 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 @@ -1834,6 +1831,16 @@ 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; -- 2.0.4