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=-10.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 6ADE0C433EC for ; Mon, 20 Jul 2020 15:42:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4515F2176B for ; Mon, 20 Jul 2020 15:42:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595259749; bh=cUT6ml9QtOqvlLfbMNEBKAVIA9b3PkIIl2rBuDmt58A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=F6748/tWvgTIIYuXBuHIsr/boGIElUby7zFkpDWQCVa+j57eiC8ADRW6TEb7JN134 4FZ+XJHBVjCfY0utvww8pDuJ20TcH3Mc1hHKwMq128ClN8xJEsUkM8r3/7lF5kdIoq HZifoy+I2Z3T1rwBPgldrx3LXojiGgWeoul4Uo48= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730084AbgGTPm2 (ORCPT ); Mon, 20 Jul 2020 11:42:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:35346 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730068AbgGTPmZ (ORCPT ); Mon, 20 Jul 2020 11:42:25 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A915120773; Mon, 20 Jul 2020 15:42:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595259745; bh=cUT6ml9QtOqvlLfbMNEBKAVIA9b3PkIIl2rBuDmt58A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XiHiuAxjYx8zkn9B4YnEatVEG8bXieE3LpTNsN5vZ8OTFmAEOeczjsriKC7Jc7ln7 44mL1FNi9zzfSZ3YLPDm7F1BvljqZ+B3fLBaSaSRgtzFecwE2F75O1WvoWuCczQmKw X0nzxzQQ40tRAtzAaPurOx3Tyhfta0NJkdxcGCPE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Cong Wang , Johannes Berg , kernel test robot , Sean Tranchetti , "David S. Miller" Subject: [PATCH 4.9 34/86] genetlink: remove genl_bind Date: Mon, 20 Jul 2020 17:36:30 +0200 Message-Id: <20200720152754.869489049@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200720152753.138974850@linuxfoundation.org> References: <20200720152753.138974850@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Sean Tranchetti [ Upstream commit 1e82a62fec613844da9e558f3493540a5b7a7b67 ] A potential deadlock can occur during registering or unregistering a new generic netlink family between the main nl_table_lock and the cb_lock where each thread wants the lock held by the other, as demonstrated below. 1) Thread 1 is performing a netlink_bind() operation on a socket. As part of this call, it will call netlink_lock_table(), incrementing the nl_table_users count to 1. 2) Thread 2 is registering (or unregistering) a genl_family via the genl_(un)register_family() API. The cb_lock semaphore will be taken for writing. 3) Thread 1 will call genl_bind() as part of the bind operation to handle subscribing to GENL multicast groups at the request of the user. It will attempt to take the cb_lock semaphore for reading, but it will fail and be scheduled away, waiting for Thread 2 to finish the write. 4) Thread 2 will call netlink_table_grab() during the (un)registration call. However, as Thread 1 has incremented nl_table_users, it will not be able to proceed, and both threads will be stuck waiting for the other. genl_bind() is a noop, unless a genl_family implements the mcast_bind() function to handle setting up family-specific multicast operations. Since no one in-tree uses this functionality as Cong pointed out, simply removing the genl_bind() function will remove the possibility for deadlock, as there is no attempt by Thread 1 above to take the cb_lock semaphore. Fixes: c380d9a7afff ("genetlink: pass multicast bind/unbind to families") Suggested-by: Cong Wang Acked-by: Johannes Berg Reported-by: kernel test robot Signed-off-by: Sean Tranchetti Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/net/genetlink.h | 8 ------- net/netlink/genetlink.c | 52 ------------------------------------------------ 2 files changed, 60 deletions(-) --- a/include/net/genetlink.h +++ b/include/net/genetlink.h @@ -33,12 +33,6 @@ struct genl_info; * do additional, common, filtering and return an error * @post_doit: called after an operation's doit callback, it may * undo operations done by pre_doit, for example release locks - * @mcast_bind: a socket bound to the given multicast group (which - * is given as the offset into the groups array) - * @mcast_unbind: a socket was unbound from the given multicast group. - * Note that unbind() will not be called symmetrically if the - * generic netlink family is removed while there are still open - * sockets. * @attrbuf: buffer to store parsed attributes * @family_list: family list * @mcgrps: multicast groups used by this family (private) @@ -61,8 +55,6 @@ struct genl_family { void (*post_doit)(const struct genl_ops *ops, struct sk_buff *skb, struct genl_info *info); - int (*mcast_bind)(struct net *net, int group); - void (*mcast_unbind)(struct net *net, int group); struct nlattr ** attrbuf; /* private */ const struct genl_ops * ops; /* private */ const struct genl_multicast_group *mcgrps; /* private */ --- a/net/netlink/genetlink.c +++ b/net/netlink/genetlink.c @@ -992,63 +992,11 @@ static const struct genl_multicast_group { .name = "notify", }, }; -static int genl_bind(struct net *net, int group) -{ - int i, err = -ENOENT; - - down_read(&cb_lock); - for (i = 0; i < GENL_FAM_TAB_SIZE; i++) { - struct genl_family *f; - - list_for_each_entry(f, genl_family_chain(i), family_list) { - if (group >= f->mcgrp_offset && - group < f->mcgrp_offset + f->n_mcgrps) { - int fam_grp = group - f->mcgrp_offset; - - if (!f->netnsok && net != &init_net) - err = -ENOENT; - else if (f->mcast_bind) - err = f->mcast_bind(net, fam_grp); - else - err = 0; - break; - } - } - } - up_read(&cb_lock); - - return err; -} - -static void genl_unbind(struct net *net, int group) -{ - int i; - - down_read(&cb_lock); - for (i = 0; i < GENL_FAM_TAB_SIZE; i++) { - struct genl_family *f; - - list_for_each_entry(f, genl_family_chain(i), family_list) { - if (group >= f->mcgrp_offset && - group < f->mcgrp_offset + f->n_mcgrps) { - int fam_grp = group - f->mcgrp_offset; - - if (f->mcast_unbind) - f->mcast_unbind(net, fam_grp); - break; - } - } - } - up_read(&cb_lock); -} - static int __net_init genl_pernet_init(struct net *net) { struct netlink_kernel_cfg cfg = { .input = genl_rcv, .flags = NL_CFG_F_NONROOT_RECV, - .bind = genl_bind, - .unbind = genl_unbind, }; /* we'll bump the group number right afterwards */