[patch 05/10] add "permit user mounts in new namespace" clone flag

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi at suse.cz>

If CLONE_NEWNS and CLONE_NEWNS_USERMNT are given to clone(2) or
unshare(2), then allow user mounts within the new namespace.

This is not flexible enough, because user mounts can't be enabled for
the initial namespace.

The remaining clone bits also getting dangerously few...

Alternatives are:

  - prctl() flag
  - setting through the containers filesystem

Signed-off-by: Miklos Szeredi <mszeredi at suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2007-04-12 13:46:19.000000000 +0200
+++ linux/fs/namespace.c	2007-04-12 13:54:36.000000000 +0200
@@ -1617,6 +1617,8 @@ struct mnt_namespace *copy_mnt_ns(int fl
 		return ns;
 
 	new_ns = dup_mnt_ns(ns, new_fs);
+	if (new_ns && (flags & CLONE_NEWNS_USERMNT))
+		new_ns->flags |= MNT_NS_PERMIT_USERMOUNTS;
 
 	put_mnt_ns(ns);
 	return new_ns;
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h	2007-04-12 13:26:48.000000000 +0200
+++ linux/include/linux/sched.h	2007-04-12 13:54:36.000000000 +0200
@@ -26,6 +26,7 @@
 #define CLONE_STOPPED		0x02000000	/* Start in stopped state */
 #define CLONE_NEWUTS		0x04000000	/* New utsname group? */
 #define CLONE_NEWIPC		0x08000000	/* New ipcs */
+#define CLONE_NEWNS_USERMNT	0x10000000	/* Allow user mounts in ns? */
 
 /*
  * Scheduling policies
Index: linux/kernel/fork.c
===================================================================
--- linux.orig/kernel/fork.c	2007-04-11 18:27:46.000000000 +0200
+++ linux/kernel/fork.c	2007-04-12 13:59:10.000000000 +0200
@@ -1586,7 +1586,7 @@ asmlinkage long sys_unshare(unsigned lon
 	err = -EINVAL;
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
-				CLONE_NEWUTS|CLONE_NEWIPC))
+				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNS_USERMNT))
 		goto bad_unshare_out;
 
 	if ((err = unshare_thread(unshare_flags)))

--