From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED0DFC43334 for ; Sun, 2 Sep 2018 23:01:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8A2E520837 for ; Sun, 2 Sep 2018 23:01:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8A2E520837 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=davemloft.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727247AbeICDTJ (ORCPT ); Sun, 2 Sep 2018 23:19:09 -0400 Received: from shards.monkeyblade.net ([23.128.96.9]:35704 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727111AbeICDTI (ORCPT ); Sun, 2 Sep 2018 23:19:08 -0400 Received: from localhost (168-64-212-66.spl.org [66.212.64.168]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 036161262C4F6; Sun, 2 Sep 2018 16:01:44 -0700 (PDT) Date: Sun, 02 Sep 2018 16:01:44 -0700 (PDT) Message-Id: <20180902.160144.542360312136980090.davem@davemloft.net> To: baijiaju1990@gmail.com Cc: ktkhai@virtuozzo.com, viro@zeniv.linux.org.uk, adobriyan@gmail.com, dvlasenk@redhat.com, xiyou.wangcong@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] net: scm: Fix a possible sleep-in-atomic-context bug in scm_fp_copy() From: David Miller In-Reply-To: <20180901100026.16956-1-baijiaju1990@gmail.com> References: <20180901100026.16956-1-baijiaju1990@gmail.com> X-Mailer: Mew version 6.7 on Emacs 26 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Sun, 02 Sep 2018 16:01:45 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jia-Ju Bai Date: Sat, 1 Sep 2018 18:00:26 +0800 > The kernel module may sleep with holding a spinlock. > > The function call paths (from bottom to top) in Linux-4.16 are: > > [FUNC] kmalloc(GFP_KERNEL) > net/core/scm.c, 85: kmalloc in scm_fp_copy > net/core/scm.c, 161: scm_fp_copy in __scm_send > ./include/net/scm.h, 88: __scm_send in scm_send > net/unix/af_unix.c, 1600: scm_send in maybe_init_creds > net/unix/af_unix.c, 1983: maybe_init_creds in unix_stream_sendpage > net/unix/af_unix.c, 1973: spin_lock in unix_stream_sendpage Please, do a full analysis of the code for these changes you are submitting. Read maybe_init_creds(), it sets msg.msg_controllen to zero. struct msghdr msg = { .msg_controllen = 0 }; When that is zero, __scm__send() is never called. static __inline__ int scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm, bool forcecreds) { ... if (msg->msg_controllen <= 0) return 0; return __scm_send(sock, msg, scm); If this bug existed, sleeping in atomic warnings would be triggering all the time and people would report that.