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[104.36.148.139]) by smtp.gmail.com with ESMTPSA id v128sm23069064pfc.14.2020.08.04.12.59.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Aug 2020 12:59:46 -0700 (PDT) Date: Tue, 4 Aug 2020 13:00:13 -0700 From: Rustam Kovhaev To: Jason Gunthorpe 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: <20200804200013.GB263814@thinkpad> References: <0000000000005b9fca05aa0af1b9@google.com> <20200731211122.GA1728751@thinkpad> <20200802222226.GO24045@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200802222226.GO24045@ziepe.ca> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 02, 2020 at 07:22:26PM -0300, Jason Gunthorpe wrote: > 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(). calling it there leads to rtnl deadlock, i think we should call net_set_todo(), so that later when we call rtnl_unlock() it will execute netdev_run_todo() and there it will proceed to calling netdev_wait_allrefs(), but in ip tunnel i will need get free_netdev() to be called after we unlock rtnl mutex i'll try to send a new patch for review > 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. good point