userns: add a user namespace owner of ipc ns

Changelog:
Feb 15: Don't set new ipc->user_ns if we didn't create a new
ipc_ns.
Feb 23: Move extern declaration to ipc_namespace.h, and group
fwd declarations at top.

Signed-off-by: Serge E. Hallyn <[e-mail]>
Acked-by: "Eric W. Biederman" <[e-mail]>
Acked-by: Daniel Lezcano <[e-mail]>
Acked-by: David Howells <[e-mail]>
Cc: James Morris <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/ipc_namespace.h

···
 
 #define IPCNS_CALLBACK_PRI 0
 
+struct user_namespace;
 
 struct ipc_ids {
 	int in_use;
···
 	unsigned int    mq_msg_max;      /* initialized to DFLT_MSGMAX */
 	unsigned int    mq_msgsize_max;  /* initialized to DFLT_MSGSIZEMAX */
 
+	/* user_ns which owns the ipc ns */
+	struct user_namespace *user_ns;
 };
 
 extern struct ipc_namespace init_ipc_ns;

ipc/msgutil.c

···
 	.mq_msg_max      = DFLT_MSGMAX,
 	.mq_msgsize_max  = DFLT_MSGSIZEMAX,
 #endif
+	.user_ns = &init_user_ns,
 };
 
 atomic_t nr_ipc_ns = ATOMIC_INIT(1);

ipc/namespace.c

···
 #include <linux/slab.h>
 #include <linux/fs.h>
 #include <linux/mount.h>
+#include <linux/user_namespace.h>
 
 #include "util.h"
 
-static struct ipc_namespace *create_ipc_ns(void)
+static struct ipc_namespace *create_ipc_ns(struct ipc_namespace *old_ns)
 {
 	struct ipc_namespace *ns;
 	int err;
···
 	ipcns_notify(IPCNS_CREATED);
 	register_ipcns_notifier(ns);
 
+	ns->user_ns = old_ns->user_ns;
+	get_user_ns(ns->user_ns);
+
 	return ns;
 }
 
···
 {
 	if (!(flags & CLONE_NEWIPC))
 		return get_ipc_ns(ns);
-	return create_ipc_ns();
+	return create_ipc_ns(ns);
 }
 
 /*
···
 	 * order to have a correct value when recomputing msgmni.
 	 */
 	ipcns_notify(IPCNS_REMOVED);
+	put_user_ns(ns->user_ns);
 }
 
 /*

kernel/nsproxy.c

···
 		err = PTR_ERR(new_nsp->ipc_ns);
 		goto out_ipc;
 	}
+	if (new_nsp->ipc_ns != tsk->nsproxy->ipc_ns) {
+		put_user_ns(new_nsp->ipc_ns->user_ns);
+		new_nsp->ipc_ns->user_ns = task_cred_xxx(tsk, user)->user_ns;
+		get_user_ns(new_nsp->ipc_ns->user_ns);
+	}
 
 	new_nsp->pid_ns = copy_pid_ns(flags, task_active_pid_ns(tsk));
 	if (IS_ERR(new_nsp->pid_ns)) {