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: Dongli Zhang <[email protected]>
---
Changed since v1:
* change the order of xenstore read in read_per_ring_refs
* use xenbus_read_unsigned() in connect_ring()
Changed since v2:
* simplify the condition check as "(err != 1 && nr_grefs > 1)"
* avoid setting err as -EINVAL to remove extra one line of code
drivers/block/xen-blkback/xenbus.c | 74 +++++++++++++++++++++-----------------
1 file changed, 41 insertions(+), 33 deletions(-)
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index a4bc74e..dfea3a4 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -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 +936,36 @@ 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);
+ nr_grefs = blkif->nr_ring_pages;
+ WARN_ON(!nr_grefs);
+
+ 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 && nr_grefs > 1) {
+ xenbus_dev_fatal(dev, err, "reading %s/%s",
+ dir, ring_ref_name);
+ return -EINVAL;
+ }
+
+ if (err != 1)
+ break;
+ }
+
if (err != 1) {
- err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", &ring_ref[0]);
+ 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;
- }
- 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];
-
- 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) {
- err = -EINVAL;
- xenbus_dev_fatal(dev, err, "reading %s/%s",
- dir, ring_ref_name);
- return err;
- }
+ return -EINVAL;
}
}
- 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 +1023,7 @@ 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);
@@ -1075,6 +1069,20 @@ static int connect_ring(struct backend_info *be)
be->blkif->nr_rings, be->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;
+ }
+
+ 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);
else {
--
2.7.4
Ping?
Dongli Zhang
On 12/19/2018 09:23 PM, Dongli Zhang wrote:
> 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: Dongli Zhang <[email protected]>
> ---
> Changed since v1:
> * change the order of xenstore read in read_per_ring_refs
> * use xenbus_read_unsigned() in connect_ring()
>
> Changed since v2:
> * simplify the condition check as "(err != 1 && nr_grefs > 1)"
> * avoid setting err as -EINVAL to remove extra one line of code
>
> drivers/block/xen-blkback/xenbus.c | 74 +++++++++++++++++++++-----------------
> 1 file changed, 41 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index a4bc74e..dfea3a4 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -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 +936,36 @@ 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);
> + nr_grefs = blkif->nr_ring_pages;
> + WARN_ON(!nr_grefs);
> +
> + 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 && nr_grefs > 1) {
> + xenbus_dev_fatal(dev, err, "reading %s/%s",
> + dir, ring_ref_name);
> + return -EINVAL;
> + }
> +
> + if (err != 1)
> + break;
> + }
> +
> if (err != 1) {
> - err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", &ring_ref[0]);
> + 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;
> - }
> - 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];
> -
> - 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) {
> - err = -EINVAL;
> - xenbus_dev_fatal(dev, err, "reading %s/%s",
> - dir, ring_ref_name);
> - return err;
> - }
> + return -EINVAL;
> }
> }
> - 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 +1023,7 @@ 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);
>
> @@ -1075,6 +1069,20 @@ static int connect_ring(struct backend_info *be)
> be->blkif->nr_rings, be->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;
> + }
> +
> + 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);
> else {
>
> -----Original Message-----
> On 12/19/2018 09:23 PM, Dongli Zhang wrote:
> > 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: Dongli Zhang <[email protected]>
> > ---
> > Changed since v1:
> > * change the order of xenstore read in read_per_ring_refs
> > * use xenbus_read_unsigned() in connect_ring()
> >
> > Changed since v2:
> > * simplify the condition check as "(err != 1 && nr_grefs > 1)"
> > * avoid setting err as -EINVAL to remove extra one line of code
> >
> > drivers/block/xen-blkback/xenbus.c | 74 +++++++++++++++++++++----------
> -------
> > 1 file changed, 41 insertions(+), 33 deletions(-)
> >
> > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-
> blkback/xenbus.c
> > index a4bc74e..dfea3a4 100644
> > --- a/drivers/block/xen-blkback/xenbus.c
> > +++ b/drivers/block/xen-blkback/xenbus.c
> > @@ -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 +936,36 @@ 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);
> > + nr_grefs = blkif->nr_ring_pages;
> > + WARN_ON(!nr_grefs);
Why not exit if !nr_grefs? There's nothing useful for this function to do in that case.
> > +
> > + 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 && nr_grefs > 1) {
> > + xenbus_dev_fatal(dev, err, "reading %s/%s",
> > + dir, ring_ref_name);
> > + return -EINVAL;
> > + }
> > +
> > + if (err != 1)
> > + break;
Seems odd to test (err != 1) twice. I'd prefer:
if (err != 1) {
if (nr_grefs == 1)
break;
<fatal error exit>
}
Either that or simply break if err != 1 and then...
> > + }
> > +
> > if (err != 1) {
...add a check and fatal error exit here if nr_grefs != 1.
> > - err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u",
> &ring_ref[0]);
> > + 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;
> > - }
> > - 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];
> > -
> > - 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) {
> > - err = -EINVAL;
> > - xenbus_dev_fatal(dev, err, "reading %s/%s",
> > - dir, ring_ref_name);
> > - return err;
> > - }
> > + return -EINVAL;
> > }
> > }
> > - 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 +1023,7 @@ 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);
> >
> > @@ -1075,6 +1069,20 @@ static int connect_ring(struct backend_info *be)
> > be->blkif->nr_rings, be->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;
> > + }
> > +
> > + be->blkif->nr_ring_pages = 1 << ring_page_order;
> > +
That's one more be->blkif. I think it's overdue to initialize a 'blkif' stack variable in this function and use that.
Paul
> > if (be->blkif->nr_rings == 1)
> > return read_per_ring_refs(&be->blkif->rings[0], dev-
> >otherend);
> > else {
> >