Re: [PATCH V2 0/2] block/scsi/dm-rq: fix leak of request private data in dm-mpath

Ming Lei
2019-07-27T02:12:40Z

On Fri, Jul 26, 2019 at 06:20:46PM +0200, Benjamin Block wrote:
> Hey Ming Lei,
>
> On Sat, Jul 20, 2019 at 11:06:35AM +0800, Ming Lei wrote:
> > Hi,
> >
> > When one request is dispatched to LLD via dm-rq, if the result is
> > BLK_STS_*RESOURCE, dm-rq will free the request. However, LLD may allocate
> > private data for this request, so this way will cause memory leak.
>
> I am confused about this. Probably because I am not up-to-date with
> all of blk-mq. But if you free the LLD private data before the request
> is finished, what is the LLD doing if the request finishes afterwards?
> Would that not be an automatic use-after-free?

Wrt. this special use case, the underlying request is totally covered by
dm-rq after .queue_rq() returns BLK_STS_*RESOURCE. So the request won't
be re-dispatched by blk-mq at all.

thanks,
Ming