| Message ID | 1547484104-20625-2-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v6,1/2] xen/blkback: add stack variable 'blkif' in connect_ring() | expand |
On Tue, Jan 15, 2019 at 12:41:44AM +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> LGTM: Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> Thanks!
On Tue, Jan 15, 2019 at 09:20:36AM +0100, Roger Pau Monné wrote: > On Tue, Jan 15, 2019 at 12:41:44AM +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> > > LGTM: > > Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> Applied. Will push out to Jens in a couple of days. Thank you! > > Thanks!
Hi Konrad, On 1/17/19 11:29 PM, Konrad Rzeszutek Wilk wrote: > On Tue, Jan 15, 2019 at 09:20:36AM +0100, Roger Pau Monné wrote: >> On Tue, Jan 15, 2019 at 12:41:44AM +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> >> >> LGTM: >> >> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> > > Applied. > > Will push out to Jens in a couple of days. Thank you! >> >> Thanks! I only see the PATCH 1/2 (xen/blkback: add stack variable 'blkif' in connect_ring()) on the top of below branch for Jens, would you please apply this one (PATCH 2/2) as well? https://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git/log/?h=linux-next 1/2 is only a prerequisite for 2/2. Thank you very much! Dongli Zhang
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index a4aadac..0878e55 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 +936,42 @@ 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]); + nr_grefs = blkif->nr_ring_pages; + + if (unlikely(!nr_grefs)) { + WARN_ON(true); + return -EINVAL; + } + + 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/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 (err != 1) { + WARN_ON(nr_grefs != 1); - if (ring_page_order > xen_blkif_max_ring_order) { + 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); @@ -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 {
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 * 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 Changed since v3: * exit at the beginning if !nr_grefs * change the if statements to avoid test (err != 1) twice * initialize a 'blkif' stack variable (refer to PATCH 1/2) Changed since v4: * use BUG_ON() when (nr_grefs == 0) to reminder the developer * set err = -EINVAL before xenbus_dev_fatal() Changed since v5: * use WARN_ON() instead of BUG_ON() drivers/block/xen-blkback/xenbus.c | 72 +++++++++++++++++++++++--------------- 1 file changed, 43 insertions(+), 29 deletions(-)