From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751911AbdITTlT (ORCPT ); Wed, 20 Sep 2017 15:41:19 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50722 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751698AbdITTlS (ORCPT ); Wed, 20 Sep 2017 15:41:18 -0400 Date: Wed, 20 Sep 2017 12:41:08 -0700 From: Ram Pai To: Dawid Ciezarkiewicz Cc: linux-kernel@vger.kernel.org, ebiederm@xmission.com Subject: Re: Read-only `slaves` with shared subtrees? Reply-To: Ram Pai References: <20170918204710.GI5698@ram.oc3035372033.ibm.com> <20170920193954.GK5698@ram.oc3035372033.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170920193954.GK5698@ram.oc3035372033.ibm.com> User-Agent: Mutt/1.5.20 (2009-12-10) X-TM-AS-GCONF: 00 x-cbid: 17092019-0020-0000-0000-00000CBD24CD X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007768; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000230; SDB=6.00919888; UDB=6.00462183; IPR=6.00700114; BA=6.00005599; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017225; XFM=3.00000015; UTC=2017-09-20 19:41:13 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17092019-0021-0000-0000-00005E35D77B Message-Id: <20170920194108.GB5721@ram.oc3035372033.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-20_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1709200262 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org sorry forgot to copy Eric. On Wed, Sep 20, 2017 at 12:39:54PM -0700, Ram Pai wrote: > On Tue, Sep 19, 2017 at 04:18:02PM -0700, Dawid Ciezarkiewicz wrote: > > On Mon, Sep 18, 2017 at 1:47 PM, Ram Pai wrote: > > > It is possible to make a slave mount readonly, by remounting it with > > > 'ro' flags. > > > > > > something like > > > > > > mount -o bind,remount,ro > > > > > > Any mount-propagation events reaching a read-only-slave does > > > inherit the slave attribute. However it does not inherit the > > > read-only attribute. > > > > I did try manually remounting, and it worked for me. If this could be > > done atomically > > (which I assume can't be, in the userspace) it could even be a workaround. > > > > > Should it inherit? or should it not? -- that has not been thought > > > off AFAICT. it think we should let it inherit. > > > > It makes sense, and it would work in my use-case. I wonder > > if that would break any existing expectations though. > > It could break existing expectations, for mounts created by propagation. > This needs to be thought through. Also Should the same semantics > apply to MNT_NOSUID, MNT_NOEXEC etc etc? > > Copying Eric. he should be able to tell if any of the container > infrastructure assumes anything about mounts propagated to read-only > mounts. > > > > > > I could at least test such a patch, it seems like a tiny change. > > Should I give it a try and submit a patch? If you could PM me any pointers > > it could help a lot since I'm not familiar with FS internals. So far I got here: > > Here is a rough patch which will accomplish what you want; not > compile-tested nor tested. > > > diff --git a/fs/namespace.c b/fs/namespace.c > index f8893dc..3239adc 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -1061,6 +1061,9 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root, > list_add_tail(&mnt->mnt_instance, &sb->s_mounts); > unlock_mount_hash(); > > + if (flag & CL_READONLY) > + mnt->mnt.mnt_flags |= MNT_READONLY; > + > if ((flag & CL_SLAVE) || > ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) { > list_add(&mnt->mnt_slave, &old->mnt_slave_list); > diff --git a/fs/pnode.c b/fs/pnode.c > index 53d411a..aeb5b47 100644 > --- a/fs/pnode.c > +++ b/fs/pnode.c > @@ -262,6 +262,8 @@ static int propagate_one(struct mount *m) > /* Notice when we are propagating across user namespaces */ > if (m->mnt_ns->user_ns != user_ns) > type |= CL_UNPRIVILEGED; > + if (m->mnt.mnt_flags & MNT_READONLY) > + type |= CL_READONLY; > child = copy_tree(last_source, last_source->mnt.mnt_root, type); > if (IS_ERR(child)) > return PTR_ERR(child); > diff --git a/fs/pnode.h b/fs/pnode.h > index dc87e65..7c59469 100644 > --- a/fs/pnode.h > +++ b/fs/pnode.h > @@ -29,6 +29,7 @@ > #define CL_SHARED_TO_SLAVE 0x20 > #define CL_UNPRIVILEGED 0x40 > #define CL_COPY_MNT_NS_FILE 0x80 > +#define CL_READONLY 0x100 > > #define CL_COPY_ALL (CL_COPY_UNBINDABLE | CL_COPY_MNT_NS_FILE) > > RP -- Ram Pai