Re: [PATCH] block/backup: fix memory leak in bdrv_backup_top_append()

[Eiichi Tsukata]

On 2019/12/23 21:40, Vladimir Sementsov-Ogievskiy wrote:
> 23.12.2019 12:06, Eiichi Tsukata wrote:
>> bdrv_open_driver() allocates bs->opaque according to drv->instance_size.
>> There is no need to allocate it and overwrite opaque in
>> bdrv_backup_top_append().
>>
>> Reproducer:
>>
>>    $ QTEST_QEMU_BINARY=./x86_64-softmmu/qemu-system-x86_64 valgrind -q 
>> --leak-check=full tests/test-replication -p /replication/secondary/start
>>    ==29792== 24 bytes in 1 blocks are definitely lost in loss record 52 of 
>> 226
>>    ==29792==    at 0x483AB1A: calloc (vg_replace_malloc.c:762)
>>    ==29792==    by 0x4B07CE0: g_malloc0 (in 
>> /usr/lib64/libglib-2.0.so.0.6000.7)
>>    ==29792==    by 0x12BAB9: bdrv_open_driver (block.c:1289)
>>    ==29792==    by 0x12BEA9: bdrv_new_open_driver (block.c:1359)
>>    ==29792==    by 0x1D15CB: bdrv_backup_top_append (backup-top.c:190)
>>    ==29792==    by 0x1CC11A: backup_job_create (backup.c:439)
>>    ==29792==    by 0x1CD542: replication_start (replication.c:544)
>>    ==29792==    by 0x1401B9: replication_start_all (replication.c:52)
>>    ==29792==    by 0x128B50: test_secondary_start (test-replication.c:427)
>>    ...
>>
>> Fixes: 7df7868b9640 ("block: introduce backup-top filter driver")
>> Signed-off-by: Eiichi Tsukata <address@hidden>
>> ---
>>   block/backup-top.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/block/backup-top.c b/block/backup-top.c
>> index 7cdb1f8eba..617217374d 100644
>> --- a/block/backup-top.c
>> +++ b/block/backup-top.c
>> @@ -196,7 +196,7 @@ BlockDriverState 
>> *bdrv_backup_top_append(BlockDriverState *source,
>>       }
>>   
>>       top->total_sectors = source->total_sectors;
>> -    top->opaque = state = g_new0(BDRVBackupTopState, 1);
>> +    state = top->opaque;
>>   
>>       bdrv_ref(target);
>>       state->target = bdrv_attach_child(top, target, "target", &child_file, 
>> errp);
>>
> 
> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> 
> Hmm, it was not my idea, I just copied it from mirror.. And there should be 
> the same leak. and
> may be in other places:
> 
> # git grep 'opaque =.*g_new'
> block/backup-top.c:    top->opaque = state = g_new0(BDRVBackupTopState, 1);
> block/file-posix.c:    state->opaque = g_new0(BDRVRawReopenState, 1);
> block/gluster.c:    state->opaque = g_new0(BDRVGlusterReopenState, 1);
> block/iscsi.c:    bs->opaque = g_new0(struct IscsiLun, 1);
> block/mirror.c:    bs_opaque = g_new0(MirrorBDSOpaque, 1);
> block/raw-format.c:    reopen_state->opaque = g_new0(BDRVRawState, 1);
> block/sheepdog.c:    re_s = state->opaque = g_new0(BDRVSheepdogReopenState, 
> 1);
> 
> 
> 

Thanks for reviewing.
As you say, block/mirror.c has similar code. But it does not cause the leak.
The difference is bdrv_mirror_top BlockDriver does not have .instance_size
whereas bdrv_backup_top_filter BlockDriver has .instance_size = 
sizeof(BDRVBackupTopState).
So when bdrv_open_driver() is called from mirror.c, g_malloc0(0) is
called allocating nothing.

Eiichi