Merge sys_clone()/sys_unshare() nsproxy and namespace handling

sys_clone() and sys_unshare() both makes copies of nsproxy and its associated
namespaces.  But they have different code paths.

This patch merges all the nsproxy and its associated namespace copy/clone
handling (as much as possible).  Posted on container list earlier for
feedback.

- Create a new nsproxy and its associated namespaces and pass it back to
  caller to attach it to right process.

- Changed all copy_*_ns() routines to return a new copy of namespace
  instead of attaching it to task->nsproxy.

- Moved the CAP_SYS_ADMIN checks out of copy_*_ns() routines.

- Removed unnessary !ns checks from copy_*_ns() and added BUG_ON()
  just incase.

- Get rid of all individual unshare_*_ns() routines and make use of
  copy_*_ns() instead.

[akpm@osdl.org: cleanups, warning fix]
[clg@fr.ibm.com: remove dup_namespaces() declaration]
[serue@us.ibm.com: fix CONFIG_IPC_NS=n, clone(CLONE_NEWIPC) retval]
[akpm@linux-foundation.org: fix build with CONFIG_SYSVIPC=n]
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <containers@lists.osdl.org>
Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/util.c

@@ -85,53 +85,20 @@ err_mem:
 	return ERR_PTR(err);
 }
 
-int unshare_ipcs(unsigned long unshare_flags, struct ipc_namespace **new_ipc)
+struct ipc_namespace *copy_ipcs(unsigned long flags, struct ipc_namespace *ns)
 {
-	struct ipc_namespace *new;
-
-	if (unshare_flags & CLONE_NEWIPC) {
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
-
-		new = clone_ipc_ns(current->nsproxy->ipc_ns);
-		if (IS_ERR(new))
-			return PTR_ERR(new);
-
-		*new_ipc = new;
-	}
-
-	return 0;
-}
-
-int copy_ipcs(unsigned long flags, struct task_struct *tsk)
-{
-	struct ipc_namespace *old_ns = tsk->nsproxy->ipc_ns;
 	struct ipc_namespace *new_ns;
-	int err = 0;
 
-	if (!old_ns)
-		return 0;
-
-	get_ipc_ns(old_ns);
+	BUG_ON(!ns);
+	get_ipc_ns(ns);
 
 	if (!(flags & CLONE_NEWIPC))
-		return 0;
+		return ns;
 
-	if (!capable(CAP_SYS_ADMIN)) {
-		err = -EPERM;
-		goto out;
-	}
+	new_ns = clone_ipc_ns(ns);
 
-	new_ns = clone_ipc_ns(old_ns);
-	if (!new_ns) {
-		err = -ENOMEM;
-		goto out;
-	}
-
-	tsk->nsproxy->ipc_ns = new_ns;
-out:
-	put_ipc_ns(old_ns);
-	return err;
+	put_ipc_ns(ns);
+	return new_ns;
 }
 
 void free_ipc_ns(struct kref *kref)
@@ -145,11 +112,11 @@ void free_ipc_ns(struct kref *kref)
 	kfree(ns);
 }
 #else
-int copy_ipcs(unsigned long flags, struct task_struct *tsk)
+struct ipc_namespace *copy_ipcs(unsigned long flags, struct ipc_namespace *ns)
 {
 	if (flags & CLONE_NEWIPC)
-		return -EINVAL;
-	return 0;
+		return ERR_PTR(-EINVAL);
+	return ns;
 }
 #endif