Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue resources at blk_release_queue())

[Hannes Reinecke <hare@suse.de>]

On 11/02/2011 01:37 PM, Jun'ichi Nomura wrote:
> On 10/31/11 22:00, Heiko Carstens wrote:
>> On Mon, Oct 31, 2011 at 08:46:06PM +0900, Jun'ichi Nomura wrote:
>>> Hm, dm_softirq_done is generic completion code of original
>>> request in dm-multipath.
>>> So oops here might be another manifestation of use-after-free.
>>>
>>> Do you always hit the oops at the same address?
>>
>> I think we saw this bug the first time. But before that the scsi
>> logging level was higher. Gonzalo is trying to recreate it with
>> the same (old) scsi logging level.
>> Afterwards we will try with barrier=0.
>>
>> Both on v3.0.7 btw.
>>
>>> Could you find corresponding source code line for
>>> the crashed address, dm_softirq_done+0x72/0x140,
>>> and which pointer was invalid?
>>
>> It crashes in the inlined function dm_done() when trying to
>> dereference tio (aka clone->end_io_data):
>>
>> static void dm_done(struct request *clone, int error, bool mapped)
>> {
>>          int r = error;
>>          struct dm_rq_target_io *tio = clone->end_io_data;
>>          dm_request_endio_fn rq_end_io = tio->ti->type->rq_end_io;
>
> Thank you. But, hmm. I have no idea about scenario.
>
> struct dm_rq_target_io is a container of clone request
> and clone->end_io_data points to its container.
>
>    struct dm_rq_target_io {
>          struct mapped_device *md;
>          struct dm_target *ti;
>          struct request *orig, clone;
>          int error;
>          union map_info info;
>    };
>
> If clone can be dereferenced, clone->end_io_data should be, too.
>
Well, actually it _always_ can be dereferenced.

At the very least we'd need to do an integrity check, ie
if the pointer 'clone->end_io_data' is indeed of the
required type.
More to the point, the end_io_data pointer could've been
assigned to something else; so even though the pointer is set
(which we don't check, either), it might not be pointing
to a 'struct dm_rq_target_io'.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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