ipc/sem: do not use ipc_rcu_free()

Avoid using ipc_rcu_free, since it just re-finds the original structure
pointer.  For the pre-list-init failure path, there is no RCU needed,
since it was just allocated.  It can be directly freed.

Link: http://lkml.kernel.org/r/20170525185107.12869-6-manfred@colorfullife.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/sem.c

@@ -258,13 +258,18 @@ static void merge_queues(struct sem_array *sma)
 	}
 }
 
+static void __sem_free(struct sem_array *sma)
+{
+	kvfree(sma);
+}
+
 static void sem_rcu_free(struct rcu_head *head)
 {
 	struct kern_ipc_perm *p = container_of(head, struct kern_ipc_perm, rcu);
 	struct sem_array *sma = container_of(p, struct sem_array, sem_perm);
 
 	security_sem_free(sma);
-	ipc_rcu_free(head);
+	__sem_free(sma);
 }
 
 /*
@@ -482,7 +487,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	sma->sem_perm.security = NULL;
 	retval = security_sem_alloc(sma);
 	if (retval) {
-		ipc_rcu_putref(&sma->sem_perm, ipc_rcu_free);
+		__sem_free(sma);
 		return retval;
 	}