On Tue, Jun 26, 2018 at 09:57:07AM +0100, David Howells wrote:
> Andrei Vagin <[email protected]> wrote:
>
> > > > > - mnt = kern_mount_data(&proc_fs_type, ns, 0);
> > >
> > > Here ns->user_ns and get_current_cred()->user_ns are not always equal
> >
> > What do you think about the attached patch?
> > ...
> > - fc = vfs_new_fs_context(&proc_fs_type, NULL, 0,
> > - FS_CONTEXT_FOR_KERNEL_MOUNT);
> > + fc = vfs_new_fs_context_userns(&proc_fs_type, NULL, 0,
> > + FS_CONTEXT_FOR_KERNEL_MOUNT, ns->user_ns);
>
> Or you could just change fc->user_ns immediately after calling
> vfs_new_fs_context(). This is what network filesystems should do with
> fc->net_ns, for example.
Ok, it works for me. The patch is attached.
>
> > -struct fs_context *vfs_new_fs_context(struct file_system_type *fs_type,
> > +struct fs_context *vfs_new_fs_context_userns(struct file_system_type
> > *fs_type,
> > struct dentry *reference,
> > unsigned int sb_flags,
> > - enum fs_context_purpose purpose)
> > + enum fs_context_purpose purpose,
> > + struct user_namespace *user_ns)
>
>
> If you'd really rather add a new parameter, please don't rename the function
> to vfs_new_fs_context_userns() - just add a new parameter. There don't need
> to be two versions of it.
>
>
> This brings me to another thought: I want to add the ability to let
> namespaces be configured by userspace, for example:
It may be a good feature, but I am not sure about procfs. A procfs
instance is created per pidns, so they should have the same owner
userns.
>
> fd = fsopen("nfs");
> sprintf(buf, "ns user %d", my_user_ns_fd);
> write(fd, buf);
> sprintf(buf, "ns net %d", my_net_ns_fd);
> write(fd, buf);
> write(fd, "s fedoraproject.org:/pub");
> write(fd, "o intr");
> ...
>
> I think therefore, I might need to insert another phase between creating the
> context and calling the filesystem initialiser:
>
> fc = vfs_new_fs_context(&afs_fs_type, mntpt, 0,
> FS_CONTEXT_FOR_SUBMOUNT);
>
> followed by:
>
> vfs_sb_set_namespace(fc, THIS_IS_USER_NS, user_ns);
> vfs_sb_set_namespace(fc, THIS_IS_NET_NS, net_ns);
>
> but then we'd need to do:
>
> vfs_begin_options(fc);
>
> before continuing (unless we made this happen automatically on the receipt of
> the first option):
>
> afs_mntpt_set_params(fc, mntpt);
> vfs_get_tree(fc);
> mnt = vfs_create_mount(fc, 0);
>
> Alternatively, we could do the namespace setting after initialisation and let
> the fs apply the changes itself.
>
> David
>From 2297ffb333a7bcee466a5273a3fc84202b9695a6 Mon Sep 17 00:00:00 2001
From: Andrei Vagin <[email protected]>
Date: Wed, 27 Jun 2018 22:45:43 -0700
Subject: [PATCH] proc: set a proper user namespace for fs_context
A user namespace should be taken from a pidns for which a procfs is created.
Signed-off-by: Andrei Vagin <[email protected]>
---
fs/proc/root.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/fs/proc/root.c b/fs/proc/root.c
index efbdc08a3c86..59aaf06a40c7 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -303,6 +303,11 @@ int pid_ns_prepare_proc(struct pid_namespace *ns)
if (IS_ERR(fc))
return PTR_ERR(fc);
+ if (fc->user_ns != ns->user_ns) {
+ put_user_ns(fc->user_ns);
+ fc->user_ns = get_user_ns(ns->user_ns);
+ }
+
ctx = fc->fs_private;
if (ctx->pid_ns != ns) {
put_pid_ns(ctx->pid_ns);
--
2.17.0
