From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dean Nelson Subject: Re: [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode Date: Mon, 11 Jun 2018 06:22:14 -0500 Message-ID: <036618ae-887f-44b5-2b39-451b81191cc1@redhat.com> References: <20180608092759.28059-1-Vadim.Lomovtsev@caviumnetworks.com> <20180610.123551.885190586229525170.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: rric@kernel.org, sgoutham@cavium.com, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Vadim.Lomovtsev@cavium.com To: David Miller , Vadim.Lomovtsev@caviumnetworks.com Return-path: In-Reply-To: <20180610.123551.885190586229525170.davem@davemloft.net> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 06/10/2018 02:35 PM, David Miller wrote: > From: Vadim Lomovtsev > Date: Fri, 8 Jun 2018 02:27:59 -0700 > >> + /* Save message data locally to prevent them from >> + * being overwritten by next ndo_set_rx_mode call(). >> + */ >> + spin_lock(&nic->rx_mode_wq_lock); >> + mode = vf_work->mode; >> + mc = vf_work->mc; >> + vf_work->mc = NULL; If I'm reading this code correctly, I believe nic->rx_mode_work.mc will have been set to NULL before the lock is dropped by nicvf_set_rx_mode_task() and acquired by nicvf_set_rx_mode(). >> + spin_unlock(&nic->rx_mode_wq_lock); > > At the moment you drop this lock, the memory behind 'mc' can be > freed up by: > >> + spin_lock(&nic->rx_mode_wq_lock); >> + kfree(nic->rx_mode_work.mc); So the kfree() will be called with a NULL pointer and quickly return. > > And you'll crash when you dereference it above via > __nicvf_set_rx_mode_task(). > I believe the call to kfree() in nicvf_set_rx_mode() is there to free up a mc_list that has been allocated by nicvf_set_rx_mode() during a previous callback to the function, one that has not yet been processed by nicvf_set_rx_mode_task(). In this way only the last 'unprocessed' callback to nicvf_set_rx_mode() gets processed should there be multiple callbacks occurring between the times the nicvf_set_rx_mode_task() runs. In my testing with this patch, this is what I see happening.