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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2080C433FE for ; Tue, 22 Feb 2022 04:28:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229862AbiBVE2z (ORCPT ); Mon, 21 Feb 2022 23:28:55 -0500 Received: from gmail-smtp-in.l.google.com ([23.128.96.19]:55608 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229893AbiBVE2w (ORCPT ); Mon, 21 Feb 2022 23:28:52 -0500 Received: from codeconstruct.com.au (pi.codeconstruct.com.au [203.29.241.158]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 798E96397 for ; Mon, 21 Feb 2022 20:17:57 -0800 (PST) Received: by codeconstruct.com.au (Postfix, from userid 10001) id 8C343202B3; Tue, 22 Feb 2022 12:17:53 +0800 (AWST) From: Matt Johnston To: netdev@vger.kernel.org Cc: "David S. Miller" , Jakub Kicinski , Jeremy Kerr Subject: [PATCH net-next v3 1/2] mctp: make __mctp_dev_get() take a refcount hold Date: Tue, 22 Feb 2022 12:17:38 +0800 Message-Id: <20220222041739.511255-2-matt@codeconstruct.com.au> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20220222041739.511255-1-matt@codeconstruct.com.au> References: <20220222041739.511255-1-matt@codeconstruct.com.au> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Previously there was a race that could allow the mctp_dev refcount to hit zero: rcu_read_lock(); mdev = __mctp_dev_get(dev); // mctp_unregister() happens here, mdev->refs hits zero mctp_dev_hold(dev); rcu_read_unlock(); Now we make __mctp_dev_get() take the hold itself. It is safe to test against the zero refcount because __mctp_dev_get() is called holding rcu_read_lock and mctp_dev uses kfree_rcu(). Reported-by: Jakub Kicinski Signed-off-by: Matt Johnston --- net/mctp/device.c | 21 ++++++++++++++++++--- net/mctp/route.c | 5 ++++- net/mctp/test/utils.c | 1 - 3 files changed, 22 insertions(+), 5 deletions(-) diff --git a/net/mctp/device.c b/net/mctp/device.c index 9e097e61f23a..b754c31162b1 100644 --- a/net/mctp/device.c +++ b/net/mctp/device.c @@ -25,12 +25,25 @@ struct mctp_dump_cb { size_t a_idx; }; -/* unlocked: caller must hold rcu_read_lock */ +/* unlocked: caller must hold rcu_read_lock. + * Returned mctp_dev has its refcount incremented, or NULL if unset. + */ struct mctp_dev *__mctp_dev_get(const struct net_device *dev) { - return rcu_dereference(dev->mctp_ptr); + struct mctp_dev *mdev = rcu_dereference(dev->mctp_ptr); + + /* RCU guarantees that any mdev is still live. + * Zero refcount implies a pending free, return NULL. + */ + if (mdev) + if (!refcount_inc_not_zero(&mdev->refs)) + return NULL; + return mdev; } +/* Returned mctp_dev does not have refcount incremented. The returned pointer + * remains live while rtnl_lock is held, as that prevents mctp_unregister() + */ struct mctp_dev *mctp_dev_get_rtnl(const struct net_device *dev) { return rtnl_dereference(dev->mctp_ptr); @@ -124,6 +137,7 @@ static int mctp_dump_addrinfo(struct sk_buff *skb, struct netlink_callback *cb) if (mdev) { rc = mctp_dump_dev_addrinfo(mdev, skb, cb); + mctp_dev_put(mdev); // Error indicates full buffer, this // callback will get retried. if (rc < 0) @@ -298,7 +312,7 @@ void mctp_dev_hold(struct mctp_dev *mdev) void mctp_dev_put(struct mctp_dev *mdev) { - if (refcount_dec_and_test(&mdev->refs)) { + if (mdev && refcount_dec_and_test(&mdev->refs)) { dev_put(mdev->dev); kfree_rcu(mdev, rcu); } @@ -370,6 +384,7 @@ static size_t mctp_get_link_af_size(const struct net_device *dev, if (!mdev) return 0; ret = nla_total_size(4); /* IFLA_MCTP_NET */ + mctp_dev_put(mdev); return ret; } diff --git a/net/mctp/route.c b/net/mctp/route.c index fe6c8bf1ec2c..6f277e56b168 100644 --- a/net/mctp/route.c +++ b/net/mctp/route.c @@ -836,7 +836,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt, { struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk); struct mctp_skb_cb *cb = mctp_cb(skb); - struct mctp_route tmp_rt; + struct mctp_route tmp_rt = {0}; struct mctp_sk_key *key; struct net_device *dev; struct mctp_hdr *hdr; @@ -948,6 +948,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt, mctp_route_release(rt); dev_put(dev); + mctp_dev_put(tmp_rt.dev); return rc; @@ -1124,11 +1125,13 @@ static int mctp_pkttype_receive(struct sk_buff *skb, struct net_device *dev, rt->output(rt, skb); mctp_route_release(rt); + mctp_dev_put(mdev); return NET_RX_SUCCESS; err_drop: kfree_skb(skb); + mctp_dev_put(mdev); return NET_RX_DROP; } diff --git a/net/mctp/test/utils.c b/net/mctp/test/utils.c index 7b7918702592..e03ba66bbe18 100644 --- a/net/mctp/test/utils.c +++ b/net/mctp/test/utils.c @@ -54,7 +54,6 @@ struct mctp_test_dev *mctp_test_create_dev(void) rcu_read_lock(); dev->mdev = __mctp_dev_get(ndev); - mctp_dev_hold(dev->mdev); rcu_read_unlock(); return dev; -- 2.32.0