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 2A48AC433FE for ; Tue, 1 Nov 2022 20:52:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229556AbiKAUwH (ORCPT ); Tue, 1 Nov 2022 16:52:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229511AbiKAUwG (ORCPT ); Tue, 1 Nov 2022 16:52:06 -0400 Received: from mail-qt1-x82e.google.com (mail-qt1-x82e.google.com [IPv6:2607:f8b0:4864:20::82e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 61C6F1AD8C for ; Tue, 1 Nov 2022 13:52:04 -0700 (PDT) Received: by mail-qt1-x82e.google.com with SMTP id l2so5435203qtq.11 for ; Tue, 01 Nov 2022 13:52:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=KbFgxpL2eDVtsTmYVTQF59QBf2g2dn88VIr3Sqq6Hfo=; b=b503HqCZbgKcjJivfpaqMA5HptPZjeY8Z3JHAUpNfCzAxXZnJRo+jti8NzIa2marfs p1BRlgO1NmKTyZdEyLZkLJc2U7D4IxwtBG4Mz3v53SE0e3Gr0s/gp0oMkOJ9U/Ny3bbp j9pl7jcWjjLKlxqR1zqjDzl1Ko1z8GbGb2YUPUnsFdXsI/0iWwqj0PD9if2WEAKh0Tdo ZwVVqbXnTDK41aVJcF9rSOmA3ubIuEJHbUgqIydAfHTG7S7pFy+klniZyRMFs/TwCLXZ 6u/xnnOHhiPyJ+LzTkvkHDAncyBVkBCFrGjgDg9T5dgYY5+5WWPczIjQAJKXTmoiv2Ic JRrA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=KbFgxpL2eDVtsTmYVTQF59QBf2g2dn88VIr3Sqq6Hfo=; b=2A6OXPRSK5SsNzkCIWGqSO2ZoNQrB6aJ9BF3P+QpbnGKHE237iy7vRA2oqXmW55e/B OfUkONLGurSOKPgS2zIexIQC9Xt/ncfs8xdxI4lUYX7tq6XjON+vioE/Iewrw7Q3TrcO fXTGHY4Gjdx83cFV0eNBEzo4F3zn0HbRUp95RvkxW7TNrt7NuhjHUxeuIFMpRwsM2TCK ZYIry0w2NhupuEKvdfKJil7FCkelAh66EApwdBGih3yOieCRDbImVDV+qUE73gGp0bYx Zcla70YMv0ebdmweFbMyKiuaHywRTyxi8ErShH5QvjJ7diSCOl0o0vCWVtF3dI3kR5S8 M3Ag== X-Gm-Message-State: ACrzQf2ZT+IOwRhU9QX2aej3AwVXALcXPmFeeHtZp1JtKr/yJhV/6ZYB 0F0umZIwyuSrylplCtBsVERKmbQs1SQ= X-Google-Smtp-Source: AMsMyM7LBfpdP9KBJY0QmEWpRebmSDKpRFU0hrRnhzu2FYhtcbWGvepvMUz0yxoc1OBtFo7rtvwT0w== X-Received: by 2002:ac8:5f51:0:b0:3a5:c72:2334 with SMTP id y17-20020ac85f51000000b003a50c722334mr17037392qta.346.1667335923186; Tue, 01 Nov 2022 13:52:03 -0700 (PDT) Received: from localhost ([2600:1700:65a0:ab60:99d6:8644:5e17:79a]) by smtp.gmail.com with ESMTPSA id i3-20020a05620a404300b006cbc6e1478csm7020982qko.57.2022.11.01.13.52.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Nov 2022 13:52:02 -0700 (PDT) Date: Tue, 1 Nov 2022 13:52:00 -0700 From: Cong Wang To: netdev@vger.kernel.org Cc: Cong Wang , shaozhengchao , Paolo Abeni , Tom Herbert Subject: Re: [Patch net] kcm: fix a race condition in kcm_recvmsg() Message-ID: References: <20221023023044.149357-1-xiyou.wangcong@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221023023044.149357-1-xiyou.wangcong@gmail.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, Oct 22, 2022 at 07:30:44PM -0700, Cong Wang wrote: > From: Cong Wang > > sk->sk_receive_queue is protected by skb queue lock, but for KCM > sockets its RX path takes mux->rx_lock to protect more than just > skb queue, so grabbing skb queue lock is not necessary when > mux->rx_lock is already held. But kcm_recvmsg() still only grabs > the skb queue lock, so race conditions still exist. > > Close this race condition by taking mux->rx_lock in kcm_recvmsg() > too. This way is much simpler than enforcing skb queue lock > everywhere. > After a second thought, this actually could introduce a performance regression as struct kcm_mux can be shared by multiple KCM sockets. So, I am afraid we have to use the skb queue lock, fortunately I found an easier way (comparing to Paolo's) to solve the skb peek race. Zhengchao, could you please test the following patch? Thanks! ----------------> diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c index a5004228111d..890a2423f559 100644 --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -222,7 +222,7 @@ static void requeue_rx_msgs(struct kcm_mux *mux, struct sk_buff_head *head) struct sk_buff *skb; struct kcm_sock *kcm; - while ((skb = __skb_dequeue(head))) { + while ((skb = skb_dequeue(head))) { /* Reset destructor to avoid calling kcm_rcv_ready */ skb->destructor = sock_rfree; skb_orphan(skb); @@ -1085,53 +1085,17 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len) return err; } -static struct sk_buff *kcm_wait_data(struct sock *sk, int flags, - long timeo, int *err) -{ - struct sk_buff *skb; - - while (!(skb = skb_peek(&sk->sk_receive_queue))) { - if (sk->sk_err) { - *err = sock_error(sk); - return NULL; - } - - if (sock_flag(sk, SOCK_DONE)) - return NULL; - - if ((flags & MSG_DONTWAIT) || !timeo) { - *err = -EAGAIN; - return NULL; - } - - sk_wait_data(sk, &timeo, NULL); - - /* Handle signals */ - if (signal_pending(current)) { - *err = sock_intr_errno(timeo); - return NULL; - } - } - - return skb; -} - static int kcm_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, int flags) { struct sock *sk = sock->sk; struct kcm_sock *kcm = kcm_sk(sk); int err = 0; - long timeo; struct strp_msg *stm; int copied = 0; struct sk_buff *skb; - timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); - - lock_sock(sk); - - skb = kcm_wait_data(sk, flags, timeo, &err); + skb = skb_recv_datagram(sk, flags, &err); if (!skb) goto out; @@ -1162,14 +1126,11 @@ static int kcm_recvmsg(struct socket *sock, struct msghdr *msg, /* Finished with message */ msg->msg_flags |= MSG_EOR; KCM_STATS_INCR(kcm->stats.rx_msgs); - skb_unlink(skb, &sk->sk_receive_queue); - kfree_skb(skb); } } out: - release_sock(sk); - + skb_free_datagram(sk, skb); return copied ? : err; } @@ -1179,7 +1140,6 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos, { struct sock *sk = sock->sk; struct kcm_sock *kcm = kcm_sk(sk); - long timeo; struct strp_msg *stm; int err = 0; ssize_t copied; @@ -1187,11 +1147,7 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos, /* Only support splice for SOCKSEQPACKET */ - timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); - - lock_sock(sk); - - skb = kcm_wait_data(sk, flags, timeo, &err); + skb = skb_recv_datagram(sk, flags, &err); if (!skb) goto err_out; @@ -1219,13 +1175,11 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos, * finish reading the message. */ - release_sock(sk); - + skb_free_datagram(sk, skb); return copied; err_out: - release_sock(sk); - + skb_free_datagram(sk, skb); return err; }