Re: memory leaks in dasd_eckd_check_characteristics() error paths

Stefan Haberland
2019-10-16T15:28:17Z

On 16.10.19 17:26, Qian Cai wrote:
> On Wed, 2019-10-16 at 16:56 +0200, Stefan Haberland wrote:
>> On 16.10.19 16:09, Qian Cai wrote:
>>> On Wed, 2019-10-16 at 15:29 +0200, Stefan Haberland wrote:
>>>> Hi,
>>>>
>>>> thanks for reporting this.
>>>>
>>>> On 02.10.19 21:33, Qian Cai wrote:
>>>>> For some reasons, dasd_eckd_check_characteristics() received -ENOMEM and then
>>>>> dasd_generic_set_online() emits this message,
>>>>>
>>>>> dasd: 0.0.0122 Setting the DASD online with discipline ECKD failed with rc=-12
>>>>>
>>>>> After that, there are several memory leaks below. There are "config_data" and
>>>>> then stored as,
>>>>>
>>>>> /* store per path conf_data */
>>>>> device->path[pos].conf_data = conf_data;
>>>>>
>>>>> When it processes the error path in  dasd_generic_set_online(), it calls
>>>>> dasd_delete_device() which nuke the whole "struct dasd_device" without freeing
>>>>> the device->path[].conf_data first.
>>>> Usually dasd_delete_device() calls dasd_generic_free_discipline() which
>>>> takes care of
>>>> the device->path[].conf_data in dasd_eckd_uncheck_device().
>>>> From a first look this looks sane.
>>>>
>>>> So I need to spend a closer look if this does not happen correctly here.
>>> When dasd_eckd_check_characteristics() failed here,
>>>
>>> if (!private) {
>>> private = kzalloc(sizeof(*private), GFP_KERNEL | GFP_DMA);
>>> if (!private) {
>>> dev_warn(&device->cdev->dev,
>>>  "Allocating memory for private DASD data "
>>>  "failed\n");
>>> return -ENOMEM;
>>> }
>>> device->private = private;
>>>
>>> The device->private is NULL.
>>>
>>> Then, in dasd_eckd_uncheck_device(), it will return immediately.
>>>
>>> if (!private)
>>> return;
>> Yes but in this case there is no per_path configuration data stored.
>> This is done after the private structure is allocated successfully.
> Yes, you are right. It has been a while so I must lost a bit memory. Actually,
> it looks like in dasd_eckd_check_characteristic() that device->private is set to
> NULL from this path,
>
> /* Read Configuration Data */
> rc = dasd_eckd_read_conf(device);
> if (rc)
> goto out_err1;
>
> out_err1:
> kfree(private->conf_data);
> kfree(device->private);
> device->private = NULL;
> return rc;
>
> because dasd_eckd_read_conf() returns -ENOMEM and calls,
>
> out_error:
> kfree(rcd_buf);
> *rcd_buffer = NULL;
> *rcd_buffer_size = 0;
> return ret;
>
> It will only free its own config_data in one operational path, but there could
> has already allocated in earlier paths in dasd_eckd_read_conf() without any
> rollback and calls return,
>
> for (lpm = 0x80; lpm; lpm>>= 1) {
> if (!(lpm & opm))
> continue;
> rc = dasd_eckd_read_conf_lpm(device, &conf_data,
>      &conf_len, lpm);
> if (rc && rc != -EOPNOTSUPP) { /* -EOPNOTSUPP is ok */
> DBF_EVENT_DEVID(DBF_WARNING, device->cdev,
> "Read configuration data returned "
> "error %d", rc);
> return rc;
> }
>
> Later, dasd_eckd_uncheck_device() see private->device is NULL without cleaning
> up. Does it make sense?

Yes, this looks like an error path not handling this correctly.

>
>>
>>>>> Is it safe to free those in
>>>>> dasd_free_device() without worrying about the double-free? Or, is it better to
>>>>> free those in dasd_eckd_check_characteristics()'s goto error handling, i.e.,
>>>>> out_err*?
>>>>>
>>>>> --- a/drivers/s390/block/dasd.c
>>>>> +++ b/drivers/s390/block/dasd.c
>>>>> @@ -153,6 +153,9 @@ struct dasd_device *dasd_alloc_device(void)
>>>>>   */
>>>>>  void dasd_free_device(struct dasd_device *device)
>>>>>  {
>>>>> +       for (int i = 0; i < 8; i++)
>>>>> +               kfree(device->path[i].conf_data);
>>>>> +
>>>>>         kfree(device->private);
>>>>>         free_pages((unsigned long) device->ese_mem, 1);
>>>>>         free_page((unsigned long) device->erp_mem);
>>>>>
>>>>>
>>>>> unreferenced object 0x0fcee900 (size 256):
>>>>>   comm "dasdconf.sh", pid 446, jiffies 4294940081 (age 170.340s)
>>>>>   hex dump (first 32 bytes):
>>>>>     dc 01 01 00 f0 f0 f2 f1 f0 f7 f9 f0 f0 c9 c2 d4  ................
>>>>>     f7 f5 f0 f0 f0 f0 f0 f0 f0 c6 d9 c2 f7 f1 62 33  ..............b3
>>>>>   backtrace:
>>>>>     [<00000000a83b1992>] kmem_cache_alloc_trace+0x200/0x388
>>>>>     [<00000000048ef3e2>] dasd_eckd_read_conf+0x408/0x1400 [dasd_eckd_mod]
>>>>>     [<00000000ce31f195>] dasd_eckd_check_characteristics+0x3cc/0x938
>>>>> [dasd_eckd_mod]
>>>>>     [<00000000f6f1759b>] dasd_generic_set_online+0x150/0x4c0
>>>>>     [<00000000efca1efa>] ccw_device_set_online+0x324/0x808
>>>>>     [<00000000f9779774>] online_store_recog_and_online+0xe8/0x220
>>>>>     [<00000000349a5446>] online_store+0x2ce/0x420
>>>>>     [<000000005bd145f8>] kernfs_fop_write+0x1bc/0x270
>>>>>     [<0000000005664197>] vfs_write+0xce/0x220
>>>>>     [<0000000044a8bccb>] ksys_write+0xea/0x190
>>>>>     [<0000000037335938>] system_call+0x296/0x2b4
>>