Re: memory leaks in dasd_eckd_check_characteristics() error paths

[Qian Cai <cai@lca.pw>]

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;

> 
> > 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
> 
>