Return-path: Received: from mail2.candelatech.com ([208.74.158.173]:32956 "EHLO mail2.candelatech.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751241AbeFHPRP (ORCPT ); Fri, 8 Jun 2018 11:17:15 -0400 Subject: Re: [PATCH v2] net-fq: Add WARN_ON check for null flow. To: Michal Kazior References: <1528415316-6379-1-git-send-email-greearb@candelatech.com> Cc: Cong Wang , Linux Kernel Network Developers , "linux-wireless@vger.kernel.org" From: Ben Greear Message-ID: <1f11144f-7580-03f4-72bd-76b0907d7ed1@candelatech.com> (sfid-20180608_171723_790861_5C6A46DA) Date: Fri, 8 Jun 2018 08:17:12 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: On 06/07/2018 04:59 PM, Cong Wang wrote: > On Thu, Jun 7, 2018 at 4:48 PM, wrote: >> diff --git a/include/net/fq_impl.h b/include/net/fq_impl.h >> index be7c0fa..cb911f0 100644 >> --- a/include/net/fq_impl.h >> +++ b/include/net/fq_impl.h >> @@ -78,7 +78,10 @@ static struct sk_buff *fq_tin_dequeue(struct fq *fq, >> return NULL; >> } >> >> - flow = list_first_entry(head, struct fq_flow, flowchain); >> + flow = list_first_entry_or_null(head, struct fq_flow, flowchain); >> + >> + if (WARN_ON_ONCE(!flow)) >> + return NULL; > > This does not make sense either. list_first_entry_or_null() > returns NULL only when the list is empty, but we already check > list_empty() right before this code, and it is protected by fq->lock. > Hello Michal, git blame shows you as the author of the fq_impl.h code. I saw a crash when debugging funky ath10k firmware in a 4.16 + hacks kernel. There was an apparent mostly-null deref in the fq_tin_dequeue method. According to gdb, it was within 1 line of the dereference of 'flow'. My hack above is probably not that useful. Cong thinks maybe the locking is bad. If you get a chance, please review this thread and see if you have any ideas for a better fix (or better debugging code). As always, if you would like me to generate you a buggy firmware that will crash in the tx path and cause all sorts of mayhem in the ath10k driver and wifi stack, I will be happy to do so. https://www.mail-archive.com/netdev@vger.kernel.org/msg239738.html Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com