Re: [PATCH v2 02/16] scsi: don't use fc_bsg_job::request and fc_bsg_job::reply directly

[Johannes Thumshirn]

On Fri, Oct 28, 2016 at 11:53:46AM +0200, Steffen Maier wrote:

[...]

> > > 
> > > > @@ -3937,6 +3944,7 @@ fc_bsg_request_handler(struct request_queue *q, struct Scsi_Host *shost,
> > > >  	struct request *req;
> > > >  	struct fc_bsg_job *job;
> > > >  	enum fc_dispatch_result ret;
> > > > +	struct fc_bsg_reply *bsg_reply;
> > > > 
> > > >  	if (!get_device(dev))
> > > >  		return;
> > > > @@ -3973,8 +3981,9 @@ fc_bsg_request_handler(struct request_queue *q, struct Scsi_Host *shost,
> > > >  		/* check if we have the msgcode value at least */
> > > >  		if (job->request_len < sizeof(uint32_t)) {
> > > >  			BUG_ON(job->reply_len < sizeof(uint32_t));
> > > > -			job->reply->reply_payload_rcv_len = 0;
> > > > -			job->reply->result = -ENOMSG;
> > > > +			bsg_reply = job->reply;
> > > > +			bsg_reply->reply_payload_rcv_len = 0;
> > > > +			bsg_reply->result = -ENOMSG;
> 
> Compiler optimization re-ordered above two lines and the first pointer
> derefence is bsg_reply->result [field offset 0] where bsg_reply is NULL.
> The assignment tries to write to memory at address NULL causing the kernel
> page fault.
> 
> Does your suggested change for [PATCH v3 02/16], shuffling the
> job->request_len checks, address above kernel page fault?

This is what I hope at least. I'm sorry but I don't have any experience with s390
and zfcp at all. I still need to get a test environment set up, but all the
people knowing how to do are rather busy at the moment. All my tests on x86_64
with FCoE and lpfc haven't had a problem so far.

Thanks,
	Johannes
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