> -----Original Message----- > From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf > Of Dongli Zhang > Sent: 07 December 2018 04:18 > To: linux-kernel@xxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx; linux- > block@xxxxxxxxxxxxxxx > Cc: axboe@xxxxxxxxx; Roger Pau Monne <roger.pau@xxxxxxxxxx>; > konrad.wilk@xxxxxxxxxx > Subject: [Xen-devel] [PATCH 1/1] xen/blkback: rework connect_ring() to > avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront > > The xenstore 'ring-page-order' is used globally for each blkback queue and > therefore should be read from xenstore only once. However, it is obtained > in read_per_ring_refs() which might be called multiple times during the > initialization of each blkback queue. That is certainly sub-optimal. > > If the blkfront is malicious and the 'ring-page-order' is set in different > value by blkfront every time before blkback reads it, this may end up at > the "WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));" in > xen_blkif_disconnect() when frontend is destroyed. I can't actually see what useful function blkif->nr_ring_pages actually performs any more. Perhaps you could actually get rid of it? > > This patch reworks connect_ring() to read xenstore 'ring-page-order' only > once. That is certainly a good thing :-) Paul > > Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx> > --- > drivers/block/xen-blkback/xenbus.c | 49 ++++++++++++++++++++++++--------- > ----- > 1 file changed, 31 insertions(+), 18 deletions(-) > > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen- > blkback/xenbus.c > index a4bc74e..4a8ce20 100644 > --- a/drivers/block/xen-blkback/xenbus.c > +++ b/drivers/block/xen-blkback/xenbus.c > @@ -919,14 +919,15 @@ static void connect(struct backend_info *be) > /* > * Each ring may have multi pages, depends on "ring-page-order". > */ > -static int read_per_ring_refs(struct xen_blkif_ring *ring, const char > *dir) > +static int read_per_ring_refs(struct xen_blkif_ring *ring, const char > *dir, > + bool use_ring_page_order) > { > unsigned int ring_ref[XENBUS_MAX_RING_GRANTS]; > struct pending_req *req, *n; > int err, i, j; > struct xen_blkif *blkif = ring->blkif; > struct xenbus_device *dev = blkif->be->dev; > - unsigned int ring_page_order, nr_grefs, evtchn; > + unsigned int nr_grefs, evtchn; > > err = xenbus_scanf(XBT_NIL, dir, "event-channel", "%u", > &evtchn); > @@ -936,28 +937,18 @@ static int read_per_ring_refs(struct xen_blkif_ring > *ring, const char *dir) > return err; > } > > - err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u", > - &ring_page_order); > - if (err != 1) { > + nr_grefs = blkif->nr_ring_pages; > + > + if (!use_ring_page_order) { > err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", > &ring_ref[0]); > if (err != 1) { > err = -EINVAL; > xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); > return err; > } > - nr_grefs = 1; > } else { > unsigned int i; > > - if (ring_page_order > xen_blkif_max_ring_order) { > - err = -EINVAL; > - xenbus_dev_fatal(dev, err, "%s/request %d ring page > order exceed max:%d", > - dir, ring_page_order, > - xen_blkif_max_ring_order); > - return err; > - } > - > - nr_grefs = 1 << ring_page_order; > for (i = 0; i < nr_grefs; i++) { > char ring_ref_name[RINGREF_NAME_LEN]; > > @@ -972,7 +963,6 @@ static int read_per_ring_refs(struct xen_blkif_ring > *ring, const char *dir) > } > } > } > - blkif->nr_ring_pages = nr_grefs; > > for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) { > req = kzalloc(sizeof(*req), GFP_KERNEL); > @@ -1030,6 +1020,8 @@ static int connect_ring(struct backend_info *be) > size_t xspathsize; > const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue- > NNN" */ > unsigned int requested_num_queues = 0; > + bool use_ring_page_order = false; > + unsigned int ring_page_order; > > pr_debug("%s %s\n", __func__, dev->otherend); > > @@ -1075,8 +1067,28 @@ static int connect_ring(struct backend_info *be) > be->blkif->nr_rings, be->blkif->blk_protocol, protocol, > pers_grants ? "persistent grants" : ""); > > + err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u", > + &ring_page_order); > + > + if (err != 1) { > + be->blkif->nr_ring_pages = 1; > + } else { > + if (ring_page_order > xen_blkif_max_ring_order) { > + err = -EINVAL; > + xenbus_dev_fatal(dev, err, > + "requested ring page order %d exceed > max:%d", > + ring_page_order, > + xen_blkif_max_ring_order); > + return err; > + } > + > + use_ring_page_order = true; > + be->blkif->nr_ring_pages = 1 << ring_page_order; > + } > + > if (be->blkif->nr_rings == 1) > - return read_per_ring_refs(&be->blkif->rings[0], dev- > >otherend); > + return read_per_ring_refs(&be->blkif->rings[0], dev->otherend, > + use_ring_page_order); > else { > xspathsize = strlen(dev->otherend) + xenstore_path_ext_size; > xspath = kmalloc(xspathsize, GFP_KERNEL); > @@ -1088,7 +1100,8 @@ static int connect_ring(struct backend_info *be) > for (i = 0; i < be->blkif->nr_rings; i++) { > memset(xspath, 0, xspathsize); > snprintf(xspath, xspathsize, "%s/queue-%u", dev- > >otherend, i); > - err = read_per_ring_refs(&be->blkif->rings[i], xspath); > + err = read_per_ring_refs(&be->blkif->rings[i], xspath, > + use_ring_page_order); > if (err) { > kfree(xspath); > return err; > -- > 2.7.4 > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxxx > https://lists.xenproject.org/mailman/listinfo/xen-devel
