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=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 4A7BFC433DF for ; Tue, 30 Jun 2020 17:50:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2FEE220772 for ; Tue, 30 Jun 2020 17:50:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388868AbgF3Ru1 (ORCPT ); Tue, 30 Jun 2020 13:50:27 -0400 Received: from alexa-out-sd-02.qualcomm.com ([199.106.114.39]:27199 "EHLO alexa-out-sd-02.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388802AbgF3Ru1 (ORCPT ); Tue, 30 Jun 2020 13:50:27 -0400 Received: from unknown (HELO ironmsg04-sd.qualcomm.com) ([10.53.140.144]) by alexa-out-sd-02.qualcomm.com with ESMTP; 30 Jun 2020 10:50:25 -0700 Received: from stranche-lnx.qualcomm.com ([129.46.14.77]) by ironmsg04-sd.qualcomm.com with ESMTP; 30 Jun 2020 10:50:24 -0700 Received: by stranche-lnx.qualcomm.com (Postfix, from userid 383980) id 2C8C54CCE; Tue, 30 Jun 2020 11:50:24 -0600 (MDT) From: Sean Tranchetti To: davem@davemloft.net, netdev@vger.kernel.org Cc: xiyou.wangcong@gmail.com, johannes.berg@intel.com, subashab@codeaurora.org, Sean Tranchetti Subject: [PATCH net v2] genetlink: remove genl_bind Date: Tue, 30 Jun 2020 11:50:17 -0600 Message-Id: <1593539417-19973-1-git-send-email-stranche@codeaurora.org> X-Mailer: git-send-email 1.9.1 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 --- include/net/genetlink.h | 8 -------- net/netlink/genetlink.c | 49 ------------------------------------------------- 2 files changed, 57 deletions(-) diff --git a/include/net/genetlink.h b/include/net/genetlink.h index 7495066..4cf703d 100644 --- a/include/net/genetlink.h +++ b/include/net/genetlink.h @@ -35,12 +35,6 @@ struct genl_multicast_group { * 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 (private) * @mcgrps: multicast groups used by this family * @n_mcgrps: number of multicast groups @@ -64,8 +58,6 @@ 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; const struct genl_multicast_group *mcgrps; diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c index 55ee680..dfaaefb 100644 --- a/net/netlink/genetlink.c +++ b/net/netlink/genetlink.c @@ -1166,60 +1166,11 @@ static int ctrl_dumppolicy(struct sk_buff *skb, struct netlink_callback *cb) .netnsok = true, }; -static int genl_bind(struct net *net, int group) -{ - struct genl_family *f; - int err = -ENOENT; - unsigned int id; - - down_read(&cb_lock); - - idr_for_each_entry(&genl_fam_idr, f, id) { - 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) -{ - struct genl_family *f; - unsigned int id; - - down_read(&cb_lock); - - idr_for_each_entry(&genl_fam_idr, f, id) { - 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 */ -- 1.9.1