From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Serge E. Hallyn" , "Eric W. Biederman" Subject: [PATCH 3.10 41/71] mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount Date: Mon, 15 Sep 2014 12:26:39 -0700 Message-Id: <20140915192640.063256868@linuxfoundation.org> In-Reply-To: <20140915192638.702282534@linuxfoundation.org> References: <20140915192638.702282534@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ 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: Greg Kroah-Hartman --- fs/namespace.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1764,9 +1764,6 @@ static int change_mount_flags(struct vfs 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, 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;