linux-kernel - Re: [PATCH v2 02/16] scsi: don't use fc_bsg_job::request and fc_bsg

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Date:   Sun, 30 Oct 2016 11:56:52 -0600
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Steffen Maier <maier@...ux.vnet.ibm.com>
Cc:     "Martin K . Petersen" <martin.petersen@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Hannes Reinecke <hare@...e.de>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Linux SCSI Mailinglist <linux-scsi@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Anil Gurumurthy <anil.gurumurthy@...gic.com>,
        Sudarsana Kalluru <sudarsana.kalluru@...gic.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Johannes Thumshirn <jth@...nel.org>,
        James Smart <james.smart@...gotech.com>,
        Dick Kennedy <dick.kennedy@...gotech.com>,
        "supporter:QLOGIC QLA2XXX FC-SCSI DRIVER" 
        <qla2xxx-upstream@...gic.com>,
        "open list:S390 ZFCP DRIVER" <linux-s390@...r.kernel.org>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>,
        "open list:FCOE SUBSYSTEM (libfc, libfcoe, fcoe)" 
        <fcoe-devel@...n-fcoe.org>
Subject: Re: [PATCH v2 02/16] scsi: don't use fc_bsg_job::request and
 fc_bsg_job::reply directly

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
-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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