On 02.02.21 18:56, Paul Durrant wrote:
From: Paul Durrant <pdurrant@xxxxxxxxxx>
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@xxxxxxxxxx>
Reviewed-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Reviewed-by: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
Pushed to xen/tip.git for-linus-5.13 Juergen
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