| From 680fca2e0a11841640cfcfba103c8e56f4951dd2 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Tue, 2 Feb 2021 17:56:59 +0000 |
| Subject: xen-blkback: fix compatibility bug with single page rings |
| MIME-Version: 1.0 |
| Content-Type: text/plain; charset=UTF-8 |
| Content-Transfer-Encoding: 8bit |
| |
| 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 { |
| -- |
| 2.30.2 |
| |