Re: [Qemu-devel] [PATCH v2 7/7] block/qcow2-refcount: fix out-of-file L2 entries to be read-as-zero

[Vladimir Sementsov-Ogievskiy]

10.10.2018 19:39, Vladimir Sementsov-Ogievskiy wrote:
> 17.08.2018 15:22, Vladimir Sementsov-Ogievskiy wrote:
>> Rewrite corrupted L2 table entry, which reference space out of
>> underlying file.
>>
>> Make this L2 table entry read-as-all-zeros without any allocation.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>> ---
>>   block/qcow2-refcount.c | 32 ++++++++++++++++++++++++++++++++
>>   1 file changed, 32 insertions(+)
>>
>> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
>> index 3c004e5bfe..3de3768a3c 100644
>> --- a/block/qcow2-refcount.c
>> +++ b/block/qcow2-refcount.c
>> @@ -1720,8 +1720,30 @@ static int check_refcounts_l2(BlockDriverState 
>> *bs, BdrvCheckResult *res,
>>               /* Mark cluster as used */
>>               csize = (((l2_entry >> s->csize_shift) & s->csize_mask) 
>> + 1) *
>>                       BDRV_SECTOR_SIZE;
>> +            if (csize > s->cluster_size) {
>> +                ret = fix_l2_entry_to_zero(
>> +                        bs, res, fix, l2_offset, i, active,
>> +                        "compressed cluster larger than cluster: 
>> size 0x%"
>> +                        PRIx64, csize);
>> +                if (ret < 0) {
>> +                    goto fail;
>> +                }
>> +                continue;
>> +            }
>> +
>>               coffset = l2_entry & s->cluster_offset_mask &
>>                         ~(BDRV_SECTOR_SIZE - 1);
>> +            if (coffset >= bdrv_getlength(bs->file->bs)) {
>> +                ret = fix_l2_entry_to_zero(
>> +                        bs, res, fix, l2_offset, i, active,
>> +                        "compressed cluster out of file: offset 0x%" 
>> PRIx64,
>> +                        coffset);
>> +                if (ret < 0) {
>> +                    goto fail;
>> +                }
>> +                continue;
>> +            }
>> +
>>               ret = qcow2_inc_refcounts_imrt(bs, res,
>>                                              refcount_table, 
>> refcount_table_size,
>>                                              coffset, csize);
>> @@ -1748,6 +1770,16 @@ static int check_refcounts_l2(BlockDriverState 
>> *bs, BdrvCheckResult *res,
>>           {
>>               uint64_t offset = l2_entry & L2E_OFFSET_MASK;
>>   +            if (offset >= bdrv_getlength(bs->file->bs)) {
>> +                ret = fix_l2_entry_to_zero(
>> +                        bs, res, fix, l2_offset, i, active,
>> +                        "cluster out of file: offset 0x%" PRIx64, 
>> offset);
>> +                if (ret < 0) {
>> +                    goto fail;
>> +                }
>> +                continue;
>> +            }
>> +
>>               if (flags & CHECK_FRAG_INFO) {
>>                   res->bfi.allocated_clusters++;
>>                   if (next_contiguous_offset &&
>
> hmm, interesting question here: in case of misaligned l2 entry, we 
> zero it out only for QCOW2_CLUSTER_ZERO_ALLOC, but not for normal 
> clusters? Why? I think it is ok to mark as zero misaligned normal 
> cluster l2 entry, otherwise we'll have fatal corruption on any 
> operation to this cluster.
>

or we can just align them down.

-- 
Best regards,
Vladimir