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

[Hannes Reinecke]

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@xxxxxxx			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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