diff options
| -rw-r--r-- | block/qcow2-refcount.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index dc8d186a82..6cbae1d205 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -466,8 +466,20 @@ static int alloc_refcount_block(BlockDriverState *bs, */ BLKDBG_EVENT(bs->file, BLKDBG_REFTABLE_GROW); - /* Calculate the number of refcount blocks needed so far */ - uint64_t blocks_used = DIV_ROUND_UP(cluster_index, s->refcount_block_size); + /* Calculate the number of refcount blocks needed so far; this will be the + * basis for calculating the index of the first cluster used for the + * self-describing refcount structures which we are about to create. + * + * Because we reached this point, there cannot be any refcount entries for + * cluster_index or higher indices yet. However, because new_block has been + * allocated to describe that cluster (and it will assume this role later + * on), we cannot use that index; also, new_block may actually have a higher + * cluster index than cluster_index, so it needs to be taken into account + * here (and 1 needs to be added to its value because that cluster is used). + */ + uint64_t blocks_used = DIV_ROUND_UP(MAX(cluster_index + 1, + (new_block >> s->cluster_bits) + 1), + s->refcount_block_size); if (blocks_used > QCOW_MAX_REFTABLE_SIZE / sizeof(uint64_t)) { return -EFBIG; |