Messages in this thread | | | Date | Wed, 20 Sep 2017 12:41:08 -0700 | From | Ram Pai <> | Subject | Re: Read-only `slaves` with shared subtrees? |
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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 <linuxram@us.ibm.com> wrote: > > > It is possible to make a slave mount readonly, by remounting it with > > > 'ro' flags. > > > > > > something like > > > > > > mount -o bind,remount,ro <slave-mount-dir> > > > > > > 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
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