Andrei Vagin [off-list ref] wrote:

quoted

quoted

quoted

-	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.

-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:

	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
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