From mboxrd@z Thu Jan 1 00:00:00 1970 From: Taehee Yoo Subject: Re: [PATCH V2 bpf] xdp: add NULL pointer check in __xdp_return() Date: Thu, 26 Jul 2018 23:02:25 +0900 Message-ID: References: <20180725150950.23298-1-ap420073@gmail.com> <20180725191149.34242252@cakuba.netronome.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Daniel Borkmann , ast@kernel.org, =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Jesper Dangaard Brouer , Netdev To: Jakub Kicinski Return-path: Received: from mail-oi0-f66.google.com ([209.85.218.66]:40522 "EHLO mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729923AbeGZPT0 (ORCPT ); Thu, 26 Jul 2018 11:19:26 -0400 Received: by mail-oi0-f66.google.com with SMTP id w126-v6so3105848oie.7 for ; Thu, 26 Jul 2018 07:02:25 -0700 (PDT) In-Reply-To: <20180725191149.34242252@cakuba.netronome.com> Sender: netdev-owner@vger.kernel.org List-ID: 2018-07-26 11:11 GMT+09:00 Jakub Kicinski : > On Thu, 26 Jul 2018 00:09:50 +0900, Taehee Yoo wrote: >> rhashtable_lookup() can return NULL. so that NULL pointer >> check routine should be added. >> >> Fixes: 02b55e5657c3 ("xdp: add MEM_TYPE_ZERO_COPY") >> Signed-off-by: Taehee Yoo >> --- >> V2 : add WARN_ON_ONCE when xa is NULL. >> >> net/core/xdp.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/net/core/xdp.c b/net/core/xdp.c >> index 9d1f220..786fdbe 100644 >> --- a/net/core/xdp.c >> +++ b/net/core/xdp.c >> @@ -345,7 +345,10 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct, >> rcu_read_lock(); >> /* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */ >> xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params); >> - xa->zc_alloc->free(xa->zc_alloc, handle); >> + if (!xa) >> + WARN_ON_ONCE(1); > > nit: is compiler smart enough to figure out the fast path here? > WARN_ON_ONCE() has the nice side effect of wrapping the condition in > unlikely(). It could save us both LoC and potentially cycles to do: > > if (!WARN_ON_ONCE(!xa)) > xa->zc_alloc->free(xa->zc_alloc, handle); > > Although it admittedly looks a bit awkward. I'm not sure if we have > some form of assert (i.e. positive check) in tree :S > Thank you for suggestion! I like this code style and I think there is no problem because readers are familiar with this code style. I will send v3 patch! Thanks! >> + else >> + xa->zc_alloc->free(xa->zc_alloc, handle); >> rcu_read_unlock(); >> default: >> /* Not possible, checked in xdp_rxq_info_reg_mem_model() */