fuse: reject internal errno

Don't allow userspace to report errors that could be kernel-internal.
Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Fixes: 334f485d ("[PATCH] FUSE - device functions")
Cc: <stable@vger.kernel.org> # v2.6.14
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dev.c

@@ -1867,7 +1867,7 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
 	}
 
 	err = -EINVAL;
-	if (oh.error <= -1000 || oh.error > 0)
+	if (oh.error <= -512 || oh.error > 0)
 		goto copy_finish;
 
 	spin_lock(&fpq->lock);