Commit 4a8c31a1 authored by Dongli Zhang's avatar Dongli Zhang Committed by Konrad Rzeszutek Wilk
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xen/blkback: rework connect_ring() to avoid inconsistent xenstore... 


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.

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.

This patch reworks connect_ring() to read xenstore 'ring-page-order' only
once.

Signed-off-by: default avatarDongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 5b8e432d

drivers/block/xen-blkback/xenbus.c

+43 −29
Original line number Diff line number Diff line
@@ -926,7 +926,7 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) 
	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);
@@ -936,43 +936,42 @@ 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) {

		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;

	nr_grefs = blkif->nr_ring_pages;



		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;

	if (unlikely(!nr_grefs)) {

		WARN_ON(true);

		return -EINVAL;

	}



		nr_grefs = 1 << ring_page_order;

	for (i = 0; i < nr_grefs; i++) {

		char ring_ref_name[RINGREF_NAME_LEN];



		snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);

		err = xenbus_scanf(XBT_NIL, dir, ring_ref_name,

				   "%u", &ring_ref[i]);



		if (err != 1) {

			if (nr_grefs == 1)

				break;



			err = -EINVAL;

			xenbus_dev_fatal(dev, err, "reading %s/%s",

					 dir, ring_ref_name);

			return err;

		}

	}



	if (err != 1) {

		WARN_ON(nr_grefs != 1);



		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;

		}

	}

	blkif->nr_ring_pages = nr_grefs;



	for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) {

		req = kzalloc(sizeof(*req), GFP_KERNEL);
@@ -1031,6 +1030,7 @@ 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;

	unsigned int ring_page_order;



	pr_debug("%s %s\n", __func__, dev->otherend);
@@ -1076,6 +1076,20 @@ static int connect_ring(struct backend_info *be) 
		 blkif->nr_rings, blkif->blk_protocol, protocol,

		 pers_grants ? "persistent grants" : "");



	ring_page_order = xenbus_read_unsigned(dev->otherend,

					       "ring-page-order", 0);



	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;

	}



	blkif->nr_ring_pages = 1 << ring_page_order;



	if (blkif->nr_rings == 1)

		return read_per_ring_refs(&blkif->rings[0], dev->otherend);

	else {

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