From: Paul Durrant pdurrant@amazon.com
[ Upstream commit d75e7f63b7c95c527cde42efb5d410d7f961498f ]
Prior to commit 4a8c31a1c6f5 ("xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront"), the behaviour of xen-blkback when connecting to a frontend was:
- read 'ring-page-order' - if not present then expect a single page ring specified by 'ring-ref' - else expect a ring specified by 'ring-refX' where X is between 0 and 1 << ring-page-order
This was correct behaviour, but was broken by the afforementioned commit to become:
- read 'ring-page-order' - if not present then expect a single page ring (i.e. ring-page-order = 0) - expect a ring specified by 'ring-refX' where X is between 0 and 1 << ring-page-order - if that didn't work then see if there's a single page ring specified by 'ring-ref'
This incorrect behaviour works most of the time but fails when a frontend that sets 'ring-page-order' is unloaded and replaced by one that does not because, instead of reading 'ring-ref', xen-blkback will read the stale 'ring-ref0' left around by the previous frontend will try to map the wrong grant reference.
This patch restores the original behaviour.
Fixes: 4a8c31a1c6f5 ("xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront") Signed-off-by: Paul Durrant pdurrant@amazon.com Reviewed-by: Dongli Zhang dongli.zhang@oracle.com Reviewed-by: "Roger Pau Monné" roger.pau@citrix.com Link: https://lore.kernel.org/r/20210202175659.18452-1-paul@xen.org Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/xen-blkback/common.h | 1 + drivers/block/xen-blkback/xenbus.c | 38 +++++++++++++----------------- 2 files changed, 17 insertions(+), 22 deletions(-)
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index b0c71d3a81a0..bda5c815e441 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -313,6 +313,7 @@ struct xen_blkif {
struct work_struct free_work; unsigned int nr_ring_pages; + bool multi_ref; /* All rings for this device. */ struct xen_blkif_ring *rings; unsigned int nr_rings; diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 9860d4842f36..6c5e9373e91c 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -998,14 +998,17 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) 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); + if (blkif->multi_ref) + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i); + else { + WARN_ON(i != 0); + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref"); + } + 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); @@ -1013,18 +1016,6 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) } }
- 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; - } - } - err = -ENOMEM; for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) { req = kzalloc(sizeof(*req), GFP_KERNEL); @@ -1129,10 +1120,15 @@ static int connect_ring(struct backend_info *be) blkif->nr_rings, blkif->blk_protocol, protocol, blkif->vbd.feature_gnt_persistent ? "persistent grants" : "");
- ring_page_order = xenbus_read_unsigned(dev->otherend, - "ring-page-order", 0); - - if (ring_page_order > xen_blkif_max_ring_order) { + err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u", + &ring_page_order); + if (err != 1) { + blkif->nr_ring_pages = 1; + blkif->multi_ref = false; + } else if (ring_page_order <= xen_blkif_max_ring_order) { + blkif->nr_ring_pages = 1 << ring_page_order; + blkif->multi_ref = true; + } else { err = -EINVAL; xenbus_dev_fatal(dev, err, "requested ring page order %d exceed max:%d", @@ -1141,8 +1137,6 @@ static int connect_ring(struct backend_info *be) 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 {