From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] net: filter: be more defensive on div/mod by X==0 Date: Mon, 07 Apr 2014 12:55:09 -0400 (EDT) Message-ID: <20140407.125509.554303783565384171.davem@davemloft.net> References: <1396652643-15647-1-git-send-email-dborkman@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: ast@plumgrid.com, netdev@vger.kernel.org To: dborkman@redhat.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:54839 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753778AbaDGQzL (ORCPT ); Mon, 7 Apr 2014 12:55:11 -0400 In-Reply-To: <1396652643-15647-1-git-send-email-dborkman@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Daniel Borkmann Date: Sat, 5 Apr 2014 01:04:03 +0200 > The old interpreter behaviour was that we returned with 0 > whenever we found a division by 0 would take place. In the new > interpreter we would currently just skip that instead and > continue execution. > > It's true that a value of 0 as return might not be appropriate > in all cases, but current users (socket filters -> drop > packet, seccomp -> SECCOMP_RET_KILL, cls_bpf -> unclassified, > etc) seem fine with that behaviour. Better this than undefined > BPF program behaviour as it's expected that A contains the > result of the division. In future, as more use cases open up, > we could further adapt this return value to our needs, if > necessary. > > So reintroduce return of 0 for division by 0 as in the old > interpreter. Also in case of K which is guaranteed to be 32bit > wide, sk_chk_filter() already takes care of preventing division > by 0 invoked through K, so we can generally spare us these tests. > > Signed-off-by: Daniel Borkmann > Reviewed-by: Alexei Starovoitov Applied, thanks Daniel.