sysvipc: fix the ipc structures initialization

A problem was found while reviewing the code after Bugzilla bug
http://bugzilla.kernel.org/show_bug.cgi?id=11796.

In ipc_addid(), the newly allocated ipc structure is inserted into the
ipcs tree (i.e made visible to readers) without locking it.  This is not
correct since its initialization continues after it has been inserted in
the tree.

This patch moves the ipc structure lock initialization + locking before
the actual insertion.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Reported-by: Clement Calmels <cboulte@gmail.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: <stable@kernel.org>		[2.6.27.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/util.c

@@ -266,9 +266,17 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 	if (ids->in_use >= size)
 		return -ENOSPC;
 
+	spin_lock_init(&new->lock);
+	new->deleted = 0;
+	rcu_read_lock();
+	spin_lock(&new->lock);
+
 	err = idr_get_new(&ids->ipcs_idr, new, &id);
-	if (err)
+	if (err) {
+		spin_unlock(&new->lock);
+		rcu_read_unlock();
 		return err;
+	}
 
 	ids->in_use++;
 
@@ -280,10 +288,6 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 		ids->seq = 0;
 
 	new->id = ipc_buildid(id, new->seq);
-	spin_lock_init(&new->lock);
-	new->deleted = 0;
-	rcu_read_lock();
-	spin_lock(&new->lock);
 	return id;
 }