[PATCH] uts: copy nsproxy only when needed

The nsproxy was being copied in unshare() when anything was being unshared,
even if it was something not referenced from nsproxy.  This should end up
in some cases with far more memory usage than necessary.
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Cc: Kirill Korotaev <dev@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Andrey Savochkin <saw@sw.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/fork.c

@@ -1606,7 +1606,7 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 	struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
 	struct files_struct *fd, *new_fd = NULL;
 	struct sem_undo_list *new_ulist = NULL;
-	struct nsproxy *new_nsproxy, *old_nsproxy;
+	struct nsproxy *new_nsproxy = NULL, *old_nsproxy = NULL;
 	struct uts_namespace *uts, *new_uts = NULL;
 
 	check_unshare_flags(&unshare_flags);
@@ -1634,18 +1634,24 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 	if ((err = unshare_utsname(unshare_flags, &new_uts)))
 		goto bad_unshare_cleanup_semundo;
 
-	if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist ||
-				new_uts) {
-
+	if (new_ns || new_uts) {
 		old_nsproxy = current->nsproxy;
 		new_nsproxy = dup_namespaces(old_nsproxy);
 		if (!new_nsproxy) {
 			err = -ENOMEM;
 			goto bad_unshare_cleanup_uts;
 		}
+	}
+
+	if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist ||
+				new_uts) {
 
 		task_lock(current);
-		current->nsproxy = new_nsproxy;
+
+		if (new_nsproxy) {
+			current->nsproxy = new_nsproxy;
+			new_nsproxy = old_nsproxy;
+		}
 
 		if (new_fs) {
 			fs = current->fs;
@@ -1687,9 +1693,11 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 		}
 
 		task_unlock(current);
-		put_nsproxy(old_nsproxy);
 	}
 
+	if (new_nsproxy)
+		put_nsproxy(new_nsproxy);
+
 bad_unshare_cleanup_uts:
 	if (new_uts)
 		put_uts_ns(new_uts);