From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:57746 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727362AbfFNMUa (ORCPT ); Fri, 14 Jun 2019 08:20:30 -0400 Date: Fri, 14 Jun 2019 14:20:09 +0200 From: Jesper Dangaard Brouer Subject: Re: [PATCH bpf 1/3] devmap: Fix premature entry free on destroying map Message-ID: <20190614142009.3922795a@carbon> In-Reply-To: <877e9octre.fsf@toke.dk> References: <20190614082015.23336-1-toshiaki.makita1@gmail.com> <20190614082015.23336-2-toshiaki.makita1@gmail.com> <877e9octre.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: xdp-newbies-owner@vger.kernel.org List-ID: To: Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNlbg==?= Cc: Toshiaki Makita , Alexei Starovoitov , Daniel Borkmann , "David S. Miller" , Jakub Kicinski , Jesper Dangaard Brouer , John Fastabend , netdev@vger.kernel.org, xdp-newbies@vger.kernel.org, bpf@vger.kernel.org, "Michael S. Tsirkin" , Jason Wang , David Ahern , brouer@redhat.com On Fri, 14 Jun 2019 13:04:53 +0200 Toke Høiland-Jørgensen wrote: > Toshiaki Makita writes: > > > dev_map_free() waits for flush_needed bitmap to be empty in order to > > ensure all flush operations have completed before freeing its entries. > > However the corresponding clear_bit() was called before using the > > entries, so the entries could be used after free. > > > > All access to the entries needs to be done before clearing the bit. > > It seems commit a5e2da6e9787 ("bpf: netdev is never null in > > __dev_map_flush") accidentally changed the clear_bit() and memory access > > order. > > > > Note that the problem happens only in __dev_map_flush(), not in > > dev_map_flush_old(). dev_map_flush_old() is called only after nulling > > out the corresponding netdev_map entry, so dev_map_free() never frees > > the entry thus no such race happens there. > > > > Fixes: a5e2da6e9787 ("bpf: netdev is never null in __dev_map_flush") > > Signed-off-by: Toshiaki Makita > > I recently posted a patch[0] that gets rid of the bitmap entirely, so I > think you can drop this one... One could argue that this is a stable tree fix... which unfortunately will cause some pain for your patch. Or maybe for the maintainers, as this is for 'bpf' git-tree and your patch is for 'bpf-next' git-tree. > [0] https://lore.kernel.org/netdev/156042464148.25684.11881534392137955942.stgit@alrua-x1/ -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer