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Tsirkin" To: Jason Wang Subject: Re: [PATCH] virtio-net: check the existence of peer before accesing its config Message-ID: <20200727061812-mutt-send-email-mst@kernel.org> References: <20200727074328.2279-1-jasowang@redhat.com> <20200727053954-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=mst@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 03:37:14 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: Cornelia Huck , qemu-devel@nongnu.org, Cindy Lu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 27, 2020 at 05:49:47PM +0800, Jason Wang wrote: > > On 2020/7/27 下午5:41, Michael S. Tsirkin wrote: > > On Mon, Jul 27, 2020 at 03:43:28PM +0800, Jason Wang wrote: > > > We try to get config from peer unconditionally which may lead NULL > > > pointer dereference. Add a check before trying to access the config. > > > > > > Fixes: 108a64818e69b ("vhost-vdpa: introduce vhost-vdpa backend") > > > Cc: Cindy Lu > > > Tested-by: Cornelia Huck > > > Signed-off-by: Jason Wang > > I am a bit lost here. Isn't this invoked > > when guest attempts to read the config? > > With no peer, what do we return to guest? > > > With no peer, it just work as in the past (read from the qemu's own emulated > config space). With a vDPA as its peer, it tries to read it from vhost-vDPA. > > > > A code comment might be helpful here. > > > Does something like above help? > > Thanks I think this part of commit log caused confusion: Add a check before trying to access the config. looking more at the code, imho in fact here is a better description of what is going on: We try to check whether a peer is VDPA in order to get config from there - with no peer, this leads to a NULL pointer dereference. Add a check before trying to access the peer type. No peer means not VDPA. > > > > > > --- > > > hw/net/virtio-net.c | 22 +++++++++++----------- > > > 1 file changed, 11 insertions(+), 11 deletions(-) > > > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > > index 4895af1cbe..935b9ef5c7 100644 > > > --- a/hw/net/virtio-net.c > > > +++ b/hw/net/virtio-net.c > > > @@ -125,6 +125,7 @@ static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config) > > > { > > > VirtIONet *n = VIRTIO_NET(vdev); > > > struct virtio_net_config netcfg; > > > + NetClientState *nc = qemu_get_queue(n->nic); > > > int ret = 0; > > > memset(&netcfg, 0 , sizeof(struct virtio_net_config)); > > > @@ -142,13 +143,12 @@ static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config) > > > VIRTIO_NET_RSS_SUPPORTED_HASHES); > > > memcpy(config, &netcfg, n->config_size); > > > - NetClientState *nc = qemu_get_queue(n->nic); > > > - if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) { > > > + if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) { > > > ret = vhost_net_get_config(get_vhost_net(nc->peer), (uint8_t *)&netcfg, > > > - n->config_size); > > > - if (ret != -1) { > > > - memcpy(config, &netcfg, n->config_size); > > > - } > > > + n->config_size); > > > + if (ret != -1) { > > > + memcpy(config, &netcfg, n->config_size); > > > + } > > > } > > > } > > > @@ -156,6 +156,7 @@ static void virtio_net_set_config(VirtIODevice *vdev, const uint8_t *config) > > > { > > > VirtIONet *n = VIRTIO_NET(vdev); > > > struct virtio_net_config netcfg = {}; > > > + NetClientState *nc = qemu_get_queue(n->nic); > > > memcpy(&netcfg, config, n->config_size); > > > @@ -166,11 +167,10 @@ static void virtio_net_set_config(VirtIODevice *vdev, const uint8_t *config) > > > qemu_format_nic_info_str(qemu_get_queue(n->nic), n->mac); > > > } > > > - NetClientState *nc = qemu_get_queue(n->nic); > > > - if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) { > > > - vhost_net_set_config(get_vhost_net(nc->peer), (uint8_t *)&netcfg, > > > - 0, n->config_size, > > > - VHOST_SET_CONFIG_TYPE_MASTER); > > > + if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) { > > > + vhost_net_set_config(get_vhost_net(nc->peer), > > > + (uint8_t *)&netcfg, 0, n->config_size, > > > + VHOST_SET_CONFIG_TYPE_MASTER); > > > } > > > } > > > -- > > > 2.20.1