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backup-top: Refuse I/O in inactive state

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When the backup-top node transitions from active to inactive in
bdrv_backup_top_drop(), the BlockCopyState is freed and the filtered
child is removed, so the node effectively becomes unusable.

However, noone told its I/O functions this, so they will happily
continue accessing bs->backing and s->bcs.  Prevent that by aborting
early when s->active is false.

(After the preceding patch, the node should be gone after
bdrv_backup_top_drop(), so this should largely be a theoretical problem.
But still, better to be safe than sorry, and also I think it just makes
sense to check s->active in the I/O functions.)

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210219153348.41861-3-mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2021-02-19 16:33:47 +01:00 committed by Kevin Wolf
parent bdc4c4c5e3
commit 705dde27c6
1 changed files with 10 additions and 0 deletions
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10
block/backup-top.c
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@ -45,6 +45,12 @@ static coroutine_fn int backup_top_co_preadv(
BlockDriverState *bs, uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
BDRVBackupTopState *s = bs->opaque;
if (!s->active) {
return -EIO;
}
return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
}
@ -54,6 +60,10 @@ static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
BDRVBackupTopState *s = bs->opaque;
uint64_t off, end;
if (!s->active) {
return -EIO;
}
if (flags & BDRV_REQ_WRITE_UNCHANGED) {
return 0;
}