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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id d46sm20955491qtk.37.2020.08.02.15.22.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 02 Aug 2020 15:22:26 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1k2MN8-002pv6-2z; Sun, 02 Aug 2020 19:22:26 -0300 Date: Sun, 2 Aug 2020 19:22:26 -0300 From: Jason Gunthorpe To: Rustam Kovhaev Cc: dledford@redhat.com, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: KASAN: use-after-free Read in netdevice_event_work_handler Message-ID: <20200802222226.GO24045@ziepe.ca> References: <0000000000005b9fca05aa0af1b9@google.com> <20200731211122.GA1728751@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200731211122.GA1728751@thinkpad> Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Fri, Jul 31, 2020 at 02:11:22PM -0700, Rustam Kovhaev wrote: > IB roce driver receives NETDEV_UNREGISTER event, calls dev_hold() and > schedules work item to execute, and before wq gets a chance to complete > it, we return to ip_tunnel.c:274 and call free_netdev(), and then later > we get UAF when scheduled function references already freed net_device > > i added verbose logging to ip_tunnel.c to see pcpu_refcnt: > + pr_info("about to free_netdev(dev) dev->pcpu_refcnt %d", netdev_refcnt_read(dev)); > > and got the following: > [ 410.220127][ T2944] ip_tunnel: about to free_netdev(dev) dev->pcpu_refcnt 8 I think there is a missing call to netdev_wait_allrefs() in the rollback_registered_many(). The normal success flow has this wait after delivering NETDEV_UNREGISTER, the error unwind for register_netdevice should as well. If the netdevice can progress to free while a dev_hold is active I think it means dev_hold is functionally useless. Jason