From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH net V3 2/2] ptr_ring: fail on large queue size (>64K) Date: Thu, 8 Feb 2018 15:11:22 +0800 Message-ID: <118d4e49-ac55-c4d3-13ed-8828b9d110a2@redhat.com> References: <1518062365-8596-1-git-send-email-jasowang@redhat.com> <1518062365-8596-2-git-send-email-jasowang@redhat.com> <20180208064602-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org To: "Michael S. Tsirkin" Return-path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:44140 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750749AbeBHHL0 (ORCPT ); Thu, 8 Feb 2018 02:11:26 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8EAA28182D05 for ; Thu, 8 Feb 2018 07:11:25 +0000 (UTC) In-Reply-To: <20180208064602-mutt-send-email-mst@kernel.org> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 2018年02月08日 12:52, Michael S. Tsirkin wrote: > On Thu, Feb 08, 2018 at 11:59:25AM +0800, Jason Wang wrote: >> We need limit the maximum size of queue, otherwise it may cause >> several side effects e.g slab will warn when the size exceeds >> KMALLOC_MAX_SIZE. Using KMALLOC_MAX_SIZE still looks too so this patch >> tries to limit it to 64K. This value could be revisited if we found a >> real case that needs more. >> >> Reported-by: syzbot+e4d4f9ddd4295539735d@syzkaller.appspotmail.com >> Fixes: 2e0ab8ca83c12 ("ptr_ring: array based FIFO for pointers") >> Signed-off-by: Jason Wang >> --- >> include/linux/ptr_ring.h | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h >> index 2af71a7..5858d48 100644 >> --- a/include/linux/ptr_ring.h >> +++ b/include/linux/ptr_ring.h >> @@ -44,6 +44,8 @@ struct ptr_ring { >> void **queue; >> }; >> > Seems like a weird location for a define. Either put defines on > top of the file, or near where they are used. I prefer the > second option. Ok. > >> +#define PTR_RING_MAX_ALLOC 65536 >> + > I guess it's an arbitrary number. Seems like a sufficiently large one, > but pls add a comment so readers don't wonder. And please explain what > it does: > > /* Callers can create ptr_ring structures with userspace-supplied > * parameters. This sets a limit on the size to make that usecase > * safe. If you ever change this, make sure to audit all callers. > */ > > Also I think we should generally use either hex 0x10000 or (1 << 16). I agree the number is arbitrary, so I still prefer the KMALLOC_MAX_SIZE especially consider it was used by pfifo_fast now. Try to limit it to an arbitrary may break lots of exist setups. E.g just google "txqueuelen 100000" can give me a lots of search results. We can do any kind of optimization on top but not for -net now. Thanks > >> /* Note: callers invoking this in a loop must use a compiler barrier, >> * for example cpu_relax(). >> * >> @@ -466,6 +468,8 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r, >> >> static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp) >> { >> + if (size > PTR_RING_MAX_ALLOC) >> + return NULL; >> return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO); >> } >> >> -- >> 2.7.4