| Message ID | 1545094538-31426-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/1] xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront | expand |
On Tue, Dec 18, 2018 at 08:55:38AM +0800, 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 <dongli.zhang@oracle.com> > --- > Changed since v1: > * change the order of xenstore read in read_per_ring_refs(suggested by Roger Pau Monne) > * use xenbus_read_unsigned() in connect_ring() (suggested by Roger Pau Monne) > > drivers/block/xen-blkback/xenbus.c | 70 ++++++++++++++++++++++---------------- > 1 file changed, 40 insertions(+), 30 deletions(-) > > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > index a4bc74e..7178f0f 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 +936,38 @@ 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) { > + 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 && (i || (!i && nr_grefs > 1))) { AFAICT the above condition can be simplified as "err != 1 && nr_grefs". > err = -EINVAL; There's no point in setting err here... > - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); > + xenbus_dev_fatal(dev, err, "reading %s/%s", > + dir, ring_ref_name); > return err; ...since you can just return -EINVAL (same applies to the other instance below). The rest LGTM, Thanks.
On Tue, Dec 18, 2018 at 10:33:00AM +0100, Roger Pau Monné wrote: > On Tue, Dec 18, 2018 at 08:55:38AM +0800, Dongli Zhang wrote: > > + 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 && (i || (!i && nr_grefs > 1))) { > > AFAICT the above condition can be simplified as "err != 1 && > nr_grefs". Sorry, this should be "err != 1 && nr_grefs > 1", since it's not order but rather the number of grefs. Roger.
Hi Roger, On 12/18/2018 05:33 PM, Roger Pau Monné wrote: > On Tue, Dec 18, 2018 at 08:55:38AM +0800, 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 <dongli.zhang@oracle.com> >> --- >> Changed since v1: >> * change the order of xenstore read in read_per_ring_refs(suggested by Roger Pau Monne) >> * use xenbus_read_unsigned() in connect_ring() (suggested by Roger Pau Monne) >> >> drivers/block/xen-blkback/xenbus.c | 70 ++++++++++++++++++++++---------------- >> 1 file changed, 40 insertions(+), 30 deletions(-) >> >> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c >> index a4bc74e..7178f0f 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 +936,38 @@ 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) { >> + 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 && (i || (!i && nr_grefs > 1))) { > > AFAICT the above condition can be simplified as "err != 1 && > nr_grefs". > >> err = -EINVAL; > > There's no point in setting err here... > >> - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); >> + xenbus_dev_fatal(dev, err, "reading %s/%s", >> + dir, ring_ref_name); >> return err; > > ...since you can just return -EINVAL (same applies to the other > instance below). I would like to confirm if I would keep the err = -EINVAL in below because most of the below code is copied from original implementation without modification. There is no err set by xenbus_read_unsigned(). + 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; For the rest, I would do something like: + 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; + } Thank you very much! Dongi Zhang
On Tue, Dec 18, 2018 at 07:31:59PM +0800, Dongli Zhang wrote: > Hi Roger, > > On 12/18/2018 05:33 PM, Roger Pau Monné wrote: > > On Tue, Dec 18, 2018 at 08:55:38AM +0800, 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 <dongli.zhang@oracle.com> > >> --- > >> Changed since v1: > >> * change the order of xenstore read in read_per_ring_refs(suggested by Roger Pau Monne) > >> * use xenbus_read_unsigned() in connect_ring() (suggested by Roger Pau Monne) > >> > >> drivers/block/xen-blkback/xenbus.c | 70 ++++++++++++++++++++++---------------- > >> 1 file changed, 40 insertions(+), 30 deletions(-) > >> > >> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > >> index a4bc74e..7178f0f 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 +936,38 @@ 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) { > >> + 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 && (i || (!i && nr_grefs > 1))) { > > > > AFAICT the above condition can be simplified as "err != 1 && > > nr_grefs". > > > >> err = -EINVAL; > > > > There's no point in setting err here... > > > >> - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); > >> + xenbus_dev_fatal(dev, err, "reading %s/%s", > >> + dir, ring_ref_name); > >> return err; > > > > ...since you can just return -EINVAL (same applies to the other > > instance below). > > I would like to confirm if I would keep the err = -EINVAL in below because most > of the below code is copied from original implementation without modification. > > There is no err set by xenbus_read_unsigned(). Right, but instead of doing: err = -EINVAL; return err; You can just do: return -EINVAL; Which is one line shorter :). > + 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; > > > For the rest, I would do something like: > > + 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; > + } > > > Thank you very much! Thanks!
On 12/18/2018 11:13 PM, Roger Pau Monné wrote: > On Tue, Dec 18, 2018 at 07:31:59PM +0800, Dongli Zhang wrote: >> Hi Roger, >> >> On 12/18/2018 05:33 PM, Roger Pau Monné wrote: >>> On Tue, Dec 18, 2018 at 08:55:38AM +0800, 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 <dongli.zhang@oracle.com> >>>> --- >>>> Changed since v1: >>>> * change the order of xenstore read in read_per_ring_refs(suggested by Roger Pau Monne) >>>> * use xenbus_read_unsigned() in connect_ring() (suggested by Roger Pau Monne) >>>> >>>> drivers/block/xen-blkback/xenbus.c | 70 ++++++++++++++++++++++---------------- >>>> 1 file changed, 40 insertions(+), 30 deletions(-) >>>> >>>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c >>>> index a4bc74e..7178f0f 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 +936,38 @@ 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) { >>>> + 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 && (i || (!i && nr_grefs > 1))) { >>> >>> AFAICT the above condition can be simplified as "err != 1 && >>> nr_grefs". >>> >>>> err = -EINVAL; >>> >>> There's no point in setting err here... >>> >>>> - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); >>>> + xenbus_dev_fatal(dev, err, "reading %s/%s", >>>> + dir, ring_ref_name); >>>> return err; >>> >>> ...since you can just return -EINVAL (same applies to the other >>> instance below). >> >> I would like to confirm if I would keep the err = -EINVAL in below because most >> of the below code is copied from original implementation without modification. >> >> There is no err set by xenbus_read_unsigned(). > > Right, but instead of doing: > > err = -EINVAL; > return err; > > You can just do: > > return -EINVAL; > > Which is one line shorter :). However, for the "ring-page-order" case, the err used in xenbus_dev_fatal() is not set as xenbus_read_unsigned() does not return any err? For "ring-page-order", I would still need to set err = -EINVAL with extra one line of code? > >> + 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; >> >> >> For the rest, I would do something like: >> >> + 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; >> + } >> >> >> Thank you very much! > > Thanks! > Dongli Zhang
On Tue, Dec 18, 2018 at 11:29:16PM +0800, Dongli Zhang wrote: > > > On 12/18/2018 11:13 PM, Roger Pau Monné wrote: > > On Tue, Dec 18, 2018 at 07:31:59PM +0800, Dongli Zhang wrote: > >> Hi Roger, > >> > >> On 12/18/2018 05:33 PM, Roger Pau Monné wrote: > >>> On Tue, Dec 18, 2018 at 08:55:38AM +0800, 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 <dongli.zhang@oracle.com> > >>>> --- > >>>> Changed since v1: > >>>> * change the order of xenstore read in read_per_ring_refs(suggested by Roger Pau Monne) > >>>> * use xenbus_read_unsigned() in connect_ring() (suggested by Roger Pau Monne) > >>>> > >>>> drivers/block/xen-blkback/xenbus.c | 70 ++++++++++++++++++++++---------------- > >>>> 1 file changed, 40 insertions(+), 30 deletions(-) > >>>> > >>>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > >>>> index a4bc74e..7178f0f 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 +936,38 @@ 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) { > >>>> + 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 && (i || (!i && nr_grefs > 1))) { > >>> > >>> AFAICT the above condition can be simplified as "err != 1 && > >>> nr_grefs". > >>> > >>>> err = -EINVAL; > >>> > >>> There's no point in setting err here... > >>> > >>>> - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); > >>>> + xenbus_dev_fatal(dev, err, "reading %s/%s", > >>>> + dir, ring_ref_name); > >>>> return err; > >>> > >>> ...since you can just return -EINVAL (same applies to the other > >>> instance below). > >> > >> I would like to confirm if I would keep the err = -EINVAL in below because most > >> of the below code is copied from original implementation without modification. > >> > >> There is no err set by xenbus_read_unsigned(). > > > > Right, but instead of doing: > > > > err = -EINVAL; > > return err; > > > > You can just do: > > > > return -EINVAL; > > > > Which is one line shorter :). > > However, for the "ring-page-order" case, the err used in xenbus_dev_fatal() is > not set as xenbus_read_unsigned() does not return any err? > > For "ring-page-order", I would still need to set err = -EINVAL with extra one > line of code? Given this, I don't have a strong opinion, so do as you please. Thanks, Roger.
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index a4bc74e..7178f0f 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 +936,38 @@ 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) { + 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 && (i || (!i && nr_grefs > 1))) { err = -EINVAL; - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); + xenbus_dev_fatal(dev, err, "reading %s/%s", + dir, ring_ref_name); return err; } - nr_grefs = 1; - } else { - unsigned int i; - if (ring_page_order > xen_blkif_max_ring_order) { + if (err != 1) + break; + } + + 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, "%s/request %d ring page order exceed max:%d", - dir, ring_page_order, - xen_blkif_max_ring_order); + xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); 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; - } - } } - 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 +1025,7 @@ 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 +1071,20 @@ 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 {
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 <dongli.zhang@oracle.com> --- Changed since v1: * change the order of xenstore read in read_per_ring_refs(suggested by Roger Pau Monne) * use xenbus_read_unsigned() in connect_ring() (suggested by Roger Pau Monne) drivers/block/xen-blkback/xenbus.c | 70 ++++++++++++++++++++++---------------- 1 file changed, 40 insertions(+), 30 deletions(-)