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bh=9XPOzXrloouJaQdbtwm84n7HpTa0lpTmNysZaux0AcU=; b=c8rOyMcKy1VBKgEJI2JKvrQ+fZZqwFoK1EzpLl+uEPmy55j6WwN5f4X+LmVwICk82Eq7gW y+0aM01Iww2O2cDTYuNjRLuqUED8LpDc8ZI6SIrMYULfltvY0gJmy/DoTHh2j7xthGjG/S 9SZkbpJfA2iWHE6n+MudeBENfuVkJ6o= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-286-7A6srA0sOYiX6MFnoBKbeg-1; Thu, 22 Apr 2021 17:34:57 -0400 X-MC-Unique: 7A6srA0sOYiX6MFnoBKbeg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5167A18B9F85; Thu, 22 Apr 2021 21:34:56 +0000 (UTC) Received: from [10.10.113.167] (ovpn-113-167.rdu2.redhat.com [10.10.113.167]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9DD4C6E6F5; Thu, 22 Apr 2021 21:34:55 +0000 (UTC) Subject: Re: [PATCH-for-6.0] net: tap: fix crash on hotplug To: Bin Meng , Peter Maydell References: <3f6be9c84782a0943ea21a8a6f8a5d055b65f2d5.1619018363.git.crobinso@redhat.com> From: Cole Robinson Message-ID: <716bf384-3ba6-179e-afa9-5b02e4573845@redhat.com> Date: Thu, 22 Apr 2021 17:34:55 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=crobinso@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=crobinso@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason Wang , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , "qemu-devel@nongnu.org Developers" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/22/21 5:42 AM, Bin Meng wrote: > On Thu, Apr 22, 2021 at 5:36 PM Peter Maydell wrote: >> >> On Thu, 22 Apr 2021 at 05:29, Bin Meng wrote: >>> >>> On Thu, Apr 22, 2021 at 12:36 AM Philippe Mathieu-Daudé >>> wrote: >>>> >>>> Cc'ing Bin. >>>> >>>> On 4/21/21 5:22 PM, Cole Robinson wrote: >>>>> Attempting to hotplug a tap nic with libvirt will crash qemu: >>>>> >>>>> $ sudo virsh attach-interface f32 network default >>>>> error: Failed to attach interface >>>>> error: Unable to read from monitor: Connection reset by peer >>>>> >>>>> 0x000055875b7f3a99 in tap_send (opaque=0x55875e39eae0) at ../net/tap.c:206 >>>>> 206 if (!s->nc.peer->do_not_pad) { >>>>> gdb$ bt >>>>> >>>>> s->nc.peer may not be set at this point. This seems to be an >>>>> expected case, as qemu_send_packet_* explicitly checks for NULL >>>>> s->nc.peer later. >>>>> >>>>> Fix it by checking for s->nc.peer here too. Padding is applied if >>>>> s->nc.peer is not set. >>>>> >>>>> https://bugzilla.redhat.com/show_bug.cgi?id=1949786 >>>>> Fixes: 969e50b61a2 >>>>> >>>>> Signed-off-by: Cole Robinson >>>>> --- >>>>> * Or should we skip padding if nc.peer is unset? I didn't dig into it >>>>> * tap-win3.c and slirp.c may need a similar fix, but the slirp case >>>>> didn't crash in a simple test. >>>>> >>>>> net/tap.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/net/tap.c b/net/tap.c >>>>> index dd42ac6134..937559dbb8 100644 >>>>> --- a/net/tap.c >>>>> +++ b/net/tap.c >>>>> @@ -203,7 +203,7 @@ static void tap_send(void *opaque) >>>>> size -= s->host_vnet_hdr_len; >>>>> } >>>>> >>>>> - if (!s->nc.peer->do_not_pad) { >>>>> + if (!s->nc.peer || !s->nc.peer->do_not_pad) { >>> >>> I think we should do: >>> >>> if (s->nc.peer && !s->nc.peer->do_not_pad) >> >> Yes. If there is no peer then the qemu_send_packet() that we're about >> to do is going to discard the packet anyway, so there's no point in >> padding it. >> >> Maybe consider >> >> static inline bool net_peer_needs_padding(NetClientState *nc) >> { >> return nc->peer && !nc->peer->do_not_pad; >> } >> >> since we want the same check in three places ? > > Sounds good to me. > I did not get to this today. Bin/Jason/anyone want to write the patch, I will test it tomorrow (US EDT time). If not I'll write the patch tomorrow. Thanks, Cole