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From e191ab6358b656764374ff1b3c7224a744dc902a Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Tue, 26 Jan 2021 17:21:02 -0500
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Subject: [PATCH 7/9] block: Require aligned image size to avoid assertion
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failure
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20210126172103.136060-2-kwolf@redhat.com>
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Patchwork-id: 100786
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O-Subject: [RHEL-8.4.0 qemu-kvm PATCH 1/2] block: Require aligned image size to avoid assertion failure
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Bugzilla: 1834281
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RH-Acked-by: Markus Armbruster <armbru@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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Unaligned requests will automatically be aligned to bl.request_alignment
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and we can't extend write requests to access space beyond the end of the
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image without resizing the image, so if we have the WRITE permission,
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but not the RESIZE one, it's required that the image size is aligned.
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Failing to meet this requirement could cause assertion failures like
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this if RESIZE permissions weren't requested:
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qemu-img: block/io.c:1910: bdrv_co_write_req_prepare: Assertion `end_sector <= bs->total_sectors || child->perm & BLK_PERM_RESIZE' failed.
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This was e.g. triggered by qemu-img converting to a target image with 4k
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request alignment when the image was only aligned to 512 bytes, but not
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to 4k.
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Turn this into a graceful error in bdrv_check_perm() so that WRITE
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without RESIZE can only be taken if the image size is aligned. If a user
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holds both permissions and drops only RESIZE, the function will return
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an error, but bdrv_child_try_set_perm() will ignore the failure silently
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if permissions are only requested to be relaxed and just keep both
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permissions while returning success.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Message-Id: <20200716142601.111237-2-kwolf@redhat.com>
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Reviewed-by: Max Reitz <mreitz@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 9c60a5d1978e6dcf85c0e01b50e6f7f54ca09104)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Jon Maloy <jmaloy.redhat.com>
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---
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block.c | 16 ++++++++++++++++
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1 file changed, 16 insertions(+)
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diff --git a/block.c b/block.c
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index 57740d312e..e9579ddf84 100644
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--- a/block.c
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+++ b/block.c
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@@ -2009,6 +2009,22 @@ static int bdrv_check_perm(BlockDriverState *bs, BlockReopenQueue *q,
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return -EPERM;
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}
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+ /*
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+ * Unaligned requests will automatically be aligned to bl.request_alignment
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+ * and without RESIZE we can't extend requests to write to space beyond the
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+ * end of the image, so it's required that the image size is aligned.
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+ */
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+ if ((cumulative_perms & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) &&
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+ !(cumulative_perms & BLK_PERM_RESIZE))
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+ {
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+ if ((bs->total_sectors * BDRV_SECTOR_SIZE) % bs->bl.request_alignment) {
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+ error_setg(errp, "Cannot get 'write' permission without 'resize': "
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+ "Image size is not a multiple of request "
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+ "alignment");
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+ return -EPERM;
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+ }
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+ }
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+
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/* Check this node */
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if (!drv) {
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return 0;
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--
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2.18.2
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