Re: [RFC][PATCH] rbind across namespaces

Ram
2005-05-21T10:08:40Z

[-- Attachment #1: Type: text/plain, Size: 648 bytes --]

On Sat, 2005-05-21 at 02:09, Miklos Szeredi wrote:
> > > I still see a problem: what if old_nd.mnt is already detached, and
> > > bind is non-recursive. Now it fails with EINVAL, though it used to
> > > work (and I think is very useful).
> >
> > I am not getting this comment. R u assuming that a detached mount
> > will have NULL namespace?
>
> Yes.
>
> > If so I dont see it being the case.
>
> See this patch:
>
> http://marc.theaimsgroup.com/?l=linux-kernel&m=111627383207049&w=2

Ok. look at the enclosed patch. Does it look any better? The special
casing for detached mounts ate up some brain cells and made the code
less simpler.

RP

[-- Attachment #2: rbind_across_namespace2.patch --]
[-- Type: text/x-patch, Size: 2955 bytes --]

Summary:

Allows rbinds across any two namespaces. NOTE: currenly bind from foriegn
namespace to current namespace is allowed. This patch now allows:

binds/rbinds from any namespace to any other namespace, under the assumption
that if a process has access to a namespace, it ought to have permission to
manipulate that namespace. The only case disallowed is a recursive bind to a
detached mount.

The patch incorporates ideas from Miklos and Jamie, and is dependent on
Miklos's "fix race in mark_mounts_for_expiry" patch to function correctly. Also
it depends on Miklos's "fix bind mount from foreign namespace" patch, because
without that patch umounts would fail.

Signed off by Ram Pai <linuxram@us.ibm.com>

--- /home/linux/views/linux-2.6.12-rc4/fs/namespace.c 2005-05-06 23:22:29.000000000 -0700
+++ linux-2.6.12-rc4/fs/namespace.c 2005-05-21 02:58:48.000000000 -0700
@@ -616,11 +616,14 @@ out_unlock:
}

/*
- * do loopback mount.
+ * do loopback mount. The loopback mount can be done from any namespace
+ * to any other namespace including the current namespace, as long as
+ * the task acquired rights to manipulate them.
*/
static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
{
struct nameidata old_nd;
+ struct namespace *mntpt_ns, *old_ns;
struct vfsmount *mnt = NULL;
int err = mount_is_safe(nd);
if (err)
@@ -631,15 +634,41 @@ static int do_loopback(struct nameidata
if (err)
return err;

- down_write(&current->namespace->sem);
err = -EINVAL;
- if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) {
- err = -ENOMEM;
- if (recurse)
- mnt = copy_tree(old_nd.mnt, old_nd.dentry);
- else
- mnt = clone_mnt(old_nd.mnt, old_nd.dentry);
+ spin_lock(&vfsmount_lock);
+
+ /*
+ * Allow all kinds of binds and rbinds except
+ * recursive bind to a detached mount
+ */
+ mntpt_ns = nd->mnt->mnt_namespace;
+ old_ns = old_nd.mnt->mnt_namespace;
+ if (!mntpt_ns || !mntpt_ns->root ||
+ (recurse && (!old_ns || !old_ns->root))) {
+ spin_unlock(&vfsmount_lock);
+ goto out;
}
+ get_namespace(mntpt_ns);
+ if (recurse && old_ns != mntpt_ns)
+ get_namespace(old_ns);
+
+ spin_unlock(&vfsmount_lock);
+
+ /*
+ * make sure we don't race with some other thread manipulating the
+ * namespaces.
+ */
+ if (recurse && (old_ns < mntpt_ns))
+ down_write(&old_ns->sem);
+ down_write(&mntpt_ns->sem);
+ if (recurse && (old_ns > mntpt_ns))
+ down_write(&old_ns->sem);
+
+ err = -ENOMEM;
+ if (recurse)
+ mnt = copy_tree(old_nd.mnt, old_nd.dentry);
+ else
+ mnt = clone_mnt(old_nd.mnt, old_nd.dentry);

if (mnt) {
/* stop bind mounts from expiring */
@@ -656,7 +685,14 @@ static int do_loopback(struct nameidata
mntput(mnt);
}

- up_write(&current->namespace->sem);
+ up_write(&mntpt_ns->sem);
+ if (recurse && (old_ns != mntpt_ns)) {
+ up_write(&old_ns->sem);
+ put_namespace(old_ns);
+ }
+ put_namespace(mntpt_ns);
+
+out:
path_release(&old_nd);
return err;
}