Commit 4a8c31a1 authored by Dongli Zhang's avatar Dongli Zhang Committed by Konrad Rzeszutek Wilk

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
...@@ -926,7 +926,7 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) ...@@ -926,7 +926,7 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
int err, i, j; int err, i, j;
struct xen_blkif *blkif = ring->blkif; struct xen_blkif *blkif = ring->blkif;
struct xenbus_device *dev = blkif->be->dev; 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", err = xenbus_scanf(XBT_NIL, dir, "event-channel", "%u",
&evtchn); &evtchn);
...@@ -936,43 +936,42 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) ...@@ -936,43 +936,42 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
return err; return err;
} }
err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u", nr_grefs = blkif->nr_ring_pages;
&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;
if (ring_page_order > xen_blkif_max_ring_order) { if (unlikely(!nr_grefs)) {
err = -EINVAL; WARN_ON(true);
xenbus_dev_fatal(dev, err, "%s/request %d ring page order exceed max:%d", return -EINVAL;
dir, ring_page_order,
xen_blkif_max_ring_order);
return err;
} }
nr_grefs = 1 << ring_page_order;
for (i = 0; i < nr_grefs; i++) { for (i = 0; i < nr_grefs; i++) {
char ring_ref_name[RINGREF_NAME_LEN]; char ring_ref_name[RINGREF_NAME_LEN];
snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i); snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
err = xenbus_scanf(XBT_NIL, dir, ring_ref_name, err = xenbus_scanf(XBT_NIL, dir, ring_ref_name,
"%u", &ring_ref[i]); "%u", &ring_ref[i]);
if (err != 1) { if (err != 1) {
if (nr_grefs == 1)
break;
err = -EINVAL; err = -EINVAL;
xenbus_dev_fatal(dev, err, "reading %s/%s", xenbus_dev_fatal(dev, err, "reading %s/%s",
dir, ring_ref_name); dir, ring_ref_name);
return err; 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++) { for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) {
req = kzalloc(sizeof(*req), GFP_KERNEL); req = kzalloc(sizeof(*req), GFP_KERNEL);
...@@ -1031,6 +1030,7 @@ static int connect_ring(struct backend_info *be) ...@@ -1031,6 +1030,7 @@ static int connect_ring(struct backend_info *be)
size_t xspathsize; size_t xspathsize;
const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */ const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */
unsigned int requested_num_queues = 0; unsigned int requested_num_queues = 0;
unsigned int ring_page_order;
pr_debug("%s %s\n", __func__, dev->otherend); pr_debug("%s %s\n", __func__, dev->otherend);
...@@ -1076,6 +1076,20 @@ static int connect_ring(struct backend_info *be) ...@@ -1076,6 +1076,20 @@ static int connect_ring(struct backend_info *be)
blkif->nr_rings, blkif->blk_protocol, protocol, blkif->nr_rings, blkif->blk_protocol, protocol,
pers_grants ? "persistent grants" : ""); 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) if (blkif->nr_rings == 1)
return read_per_ring_refs(&blkif->rings[0], dev->otherend); return read_per_ring_refs(&blkif->rings[0], dev->otherend);
else { else {
......
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