| Message ID | 20210128125528.11695-1-paul@xen.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xen-blkback: fix compatibility bug with single page rings | expand |
Apologies; I missed the v2 from the subject line. I'll re-send. Paul > -----Original Message----- > From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf Of Paul Durrant > Sent: 28 January 2021 12:55 > To: xen-devel@lists.xenproject.org; linux-block@vger.kernel.org; linux-kernel@vger.kernel.org > Cc: Paul Durrant <pdurrant@amazon.com>; Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; Roger Pau > Monné <roger.pau@citrix.com>; Jens Axboe <axboe@kernel.dk>; Dongli Zhang <dongli.zhang@oracle.com> > Subject: [PATCH] xen-blkback: fix compatibility bug with single page rings > > From: Paul Durrant <pdurrant@amazon.com> > > 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> > --- > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Cc: "Roger Pau Monné" <roger.pau@citrix.com> > Cc: Jens Axboe <axboe@kernel.dk> > Cc: Dongli Zhang <dongli.zhang@oracle.com> > > v2: > - Remove now-spurious error path special-case when nr_grefs == 1 > --- > 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..524a79f10de6 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 { > -- > 2.17.1 >
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index b0c71d3a81a0..524a79f10de6 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 {