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 A89D9C433FE for ; Tue, 15 Mar 2022 03:03:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344531AbiCODEQ (ORCPT ); Mon, 14 Mar 2022 23:04:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38130 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235139AbiCODEM (ORCPT ); Mon, 14 Mar 2022 23:04:12 -0400 Received: from mail-pj1-x102b.google.com (mail-pj1-x102b.google.com [IPv6:2607:f8b0:4864:20::102b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D77D2BEB; Mon, 14 Mar 2022 20:03:01 -0700 (PDT) Received: by mail-pj1-x102b.google.com with SMTP id d10-20020a17090a7bca00b001c5ed9a196bso881255pjl.1; Mon, 14 Mar 2022 20:03:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=A455krXMhhy8/LLYYm9vWAWvlzZHEKZiVzhbnonkNws=; b=jhcAENCFBWZcmbZIoMa4IBixoqkt2DRSnQnBe9VESilKn4CEEqf3AYoyR3vIQxCdYT pJ+KMvc61kTkjENj0c10iWam3OS9WYzsndLB5E34Ru/pUPujcpJbqVYOLXqfKhvd4fot XgGUmP9Cr1T5I1WTZkKbsF1ffq004PWTUxMhwfC5XLQsCoShyIrrHRJGUZlHhMfsVEsv rmkth4GoRFsGnAcqW5wn6vwbBocXG/NjFw/ENW+cBadja5I4eFnsFvyFcsdz5TixPIcB Hl3+OhGXuMwXX84KMLTToAUySmj2HtArumZLaOGNxGf8xnVP6qSTN3A2OkEZFq6OdrfE DJDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=A455krXMhhy8/LLYYm9vWAWvlzZHEKZiVzhbnonkNws=; b=qQihNDoEpg8sL6a1Znwdl/KZMCeypuGTxQJUSlpVx6D6Fzec5XxR4ZKS2JaPu7VHgT 5W7F7PUCbAmxw5vt23v4lSbfvykqNf9JbYFus9k313OBxfcyqe9d30tmN/B9FfyyH1v/ wTbH9H0XwbFIrbgEmmzbOc6jMejaHAJ1GRn2DWePukEOEYrcPlgT+znHF5rdp9dVKxB/ 3xdhYPWmtDCeTUkg19n1cbdNnL+e0Zc3nQJKstYuBMfg1i2Enu4/O3OnfXHs9Tqa9lQP z1GPqRMRkc2w6mzSB8YOWmBSHTgm8yGFPDN04pVwQSws2/OsC9fqti+wCgv7FbsOS2GG wATg== X-Gm-Message-State: AOAM532WcS0qe8HgTCxzIWlEOtgauZ27PaVudcHR4H0tgGQ03sQjyzQr v29j5CeLB3/YgKb/2sEbnHc= X-Google-Smtp-Source: ABdhPJxqfei84nWaWhmazei5KQRCXRBg/w+OzFuE2RAB+U8R7E8cDTc51FKfTxQjkb3idYtcSGwKdw== X-Received: by 2002:a17:902:8a85:b0:151:b3c6:87f8 with SMTP id p5-20020a1709028a8500b00151b3c687f8mr26208994plo.129.1647313380664; Mon, 14 Mar 2022 20:03:00 -0700 (PDT) Received: from [192.168.86.21] (c-73-241-150-58.hsd1.ca.comcast.net. [73.241.150.58]) by smtp.gmail.com with ESMTPSA id w3-20020a63af03000000b00381309eb407sm6290291pge.68.2022.03.14.20.02.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Mar 2022 20:03:00 -0700 (PDT) Message-ID: Date: Mon, 14 Mar 2022 20:02:54 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.0 Subject: Re: [PATCH net V4 2/2] ax25: Fix NULL pointer dereferences in ax25 timers Content-Language: en-US To: Duoming Zhou , linux-hams@vger.kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kuba@kernel.org, davem@davemloft.net, ralf@linux-mips.org, jreuter@yaina.de, dan.carpenter@oracle.com References: <20220315015654.79941-1-duoming@zju.edu.cn> From: Eric Dumazet In-Reply-To: <20220315015654.79941-1-duoming@zju.edu.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/14/22 18:56, Duoming Zhou wrote: > There are race conditions that may lead to null pointer dereferences in > ax25_heartbeat_expiry(), ax25_t1timer_expiry(), ax25_t2timer_expiry(), > ax25_t3timer_expiry() and ax25_idletimer_expiry(), when we use > ax25_kill_by_device() to detach the ax25 device. > > One of the race conditions that cause null pointer dereferences can be > shown as below: > > (Thread 1) | (Thread 2) > ax25_connect() | > ax25_std_establish_data_link() | > ax25_start_t1timer() | > mod_timer(&ax25->t1timer,..) | > | ax25_kill_by_device() > (wait a time) | ... > | s->ax25_dev = NULL; //(1) > ax25_t1timer_expiry() | > ax25->ax25_dev->values[..] //(2)| ... > ... | > > We set null to ax25_cb->ax25_dev in position (1) and dereference > the null pointer in position (2). > > The corresponding fail log is shown below: > =============================================================== > BUG: kernel NULL pointer dereference, address: 0000000000000050 > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.17.0-rc6-00794-g45690b7d0 > RIP: 0010:ax25_t1timer_expiry+0x12/0x40 > ... > Call Trace: > call_timer_fn+0x21/0x120 > __run_timers.part.0+0x1ca/0x250 > run_timer_softirq+0x2c/0x60 > __do_softirq+0xef/0x2f3 > irq_exit_rcu+0xb6/0x100 > sysvec_apic_timer_interrupt+0xa2/0xd0 > ... > > This patch uses ax25_disconnect() to delete timers before we set null to > ax25_cb->ax25_dev in ax25_kill_by_device().The function ax25_disconnect() > will not return until all timers are stopped, because we have changed > del_timer() to del_timer_sync(). What`s more, we add condition check in > ax25_destroy_socket(), because ax25_stop_heartbeat() will not return, > if there is still heartbeat. > > Signed-off-by: Duoming Zhou Missing FIxes: tag ? > --- > Changes in V4: > - Based on [PATCH net V4 1/2] ax25: Fix refcount leaks caused by ax25_cb_del(). > > net/ax25/af_ax25.c | 7 ++++--- > net/ax25/ax25_timer.c | 10 +++++----- > 2 files changed, 9 insertions(+), 8 deletions(-) > > diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c > index 0886109421a..dc6161a75a1 100644 > --- a/net/ax25/af_ax25.c > +++ b/net/ax25/af_ax25.c > @@ -89,20 +89,20 @@ static void ax25_kill_by_device(struct net_device *dev) > sk = s->sk; > if (!sk) { > spin_unlock_bh(&ax25_list_lock); > - s->ax25_dev = NULL; > ax25_disconnect(s, ENETUNREACH); > + s->ax25_dev = NULL; > spin_lock_bh(&ax25_list_lock); > goto again; > } > sock_hold(sk); > spin_unlock_bh(&ax25_list_lock); > lock_sock(sk); > + ax25_disconnect(s, ENETUNREACH); > s->ax25_dev = NULL; > if (sk->sk_wq) { > dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker); > ax25_dev_put(ax25_dev); > } > - ax25_disconnect(s, ENETUNREACH); > release_sock(sk); > spin_lock_bh(&ax25_list_lock); > sock_put(sk); > @@ -307,7 +307,8 @@ void ax25_destroy_socket(ax25_cb *ax25) > > ax25_cb_del(ax25); > > - ax25_stop_heartbeat(ax25); > + if (!ax25->sk || !sock_flag(ax25->sk, SOCK_DESTROY)) > + ax25_stop_heartbeat(ax25); > ax25_stop_t1timer(ax25); > ax25_stop_t2timer(ax25); > ax25_stop_t3timer(ax25); > diff --git a/net/ax25/ax25_timer.c b/net/ax25/ax25_timer.c > index 85865ebfdfa..99af3d1aeec 100644 > --- a/net/ax25/ax25_timer.c > +++ b/net/ax25/ax25_timer.c > @@ -78,27 +78,27 @@ void ax25_start_idletimer(ax25_cb *ax25) > > void ax25_stop_heartbeat(ax25_cb *ax25) > { > - del_timer(&ax25->timer); > + del_timer_sync(&ax25->timer); > } > > void ax25_stop_t1timer(ax25_cb *ax25) > { > - del_timer(&ax25->t1timer); > + del_timer_sync(&ax25->t1timer); > } > > void ax25_stop_t2timer(ax25_cb *ax25) > { > - del_timer(&ax25->t2timer); > + del_timer_sync(&ax25->t2timer); > } > > void ax25_stop_t3timer(ax25_cb *ax25) > { > - del_timer(&ax25->t3timer); > + del_timer_sync(&ax25->t3timer); > } > > void ax25_stop_idletimer(ax25_cb *ax25) > { > - del_timer(&ax25->idletimer); > + del_timer_sync(&ax25->idletimer); > } > > int ax25_t1timer_running(ax25_cb *ax25) Are you sure calling del_time_sync() wont deadlock ? If the timer handlers need a lock owned by the thread calling del_timer_sync(), then this will block forever. Usually, we make sure each active timer owns a reference (sk_stop_timer() for example)