Paul Durrant f276d195ce xen-blkback: fix compatibility bug with single page rings ... [ Upstream commit d75e7f63b7c95c527cde42efb5d410d7f961498f ] Prior to commit 4a8c31a1c6 ("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: 4a8c31a1c6 ("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>		2021-05-14 09:44:23 +02:00
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Makefile	treewide: Add SPDX license identifier - Makefile/Kconfig	2019-05-21 10:50:46 +02:00
blkback.c	xen-blkback: don't leak persistent grants from xen_blkbk_map()	2021-03-30 14:35:30 +02:00
common.h	xen-blkback: fix compatibility bug with single page rings	2021-05-14 09:44:23 +02:00
xenbus.c	xen-blkback: fix compatibility bug with single page rings	2021-05-14 09:44:23 +02:00