linux-kernel - Re: [PATCH v2 1/1] scsi: fc: check for rport presence in fc_block_scsi

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Date:   Tue, 26 Sep 2017 11:09:13 +0200
From:   Steffen Maier <maier@...ux.vnet.ibm.com>
To:     Johannes Thumshirn <jthumshirn@...e.de>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Cc:     Linux SCSI Mailinglist <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Hannes Reinecke <hare@...e.de>,
        Bart Van Assche <Bart.VanAssche@...disk.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 1/1] scsi: fc: check for rport presence in
 fc_block_scsi_eh

On 09/26/2017 08:58 AM, Johannes Thumshirn wrote:
> Coverity-scan recently found a possible NULL pointer dereference in
> fc_block_scsi_eh() as starget_to_rport() either returns the rport for
> the startget or NULL.
> 
> While it is rather unlikely to have fc_block_scsi_eh() called without
> an rport associated it's a good idea to catch potential misuses of the
> API gracefully.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> Reviewed-by: Bart Van Assche <bart.vanassche@....com>
> ---
> 
> Changes since v1:
> - s/WARN_ON/WARN_ON_ONCE/ (Bart)
> 
> ---
>   drivers/scsi/scsi_transport_fc.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
> index ba9d70f8a6a1..38abff7b5dbc 100644
> --- a/drivers/scsi/scsi_transport_fc.c
> +++ b/drivers/scsi/scsi_transport_fc.c
> @@ -3328,6 +3328,9 @@ int fc_block_scsi_eh(struct scsi_cmnd *cmnd)
>   {
>   	struct fc_rport *rport = starget_to_rport(scsi_target(cmnd->device));
> 
> +	if (WARN_ON_ONCE(!rport))
> +		return 0;

Good idea.

However, return 0 or FAST_IO_FAIL?
I mean the callchains to this function (and of fc_block_rport()) react 
differently depending on the return value.
Returning 0 means that the rport left the blocked state, i.e. is usable 
for traffic again.
If there is no rport at all, I suppose one cannot use it for traffic.
If there is any I/O pending on this scope and we return 0, scsi_eh 
escalates; and if this happens for a host_reset we end up with offlined 
scsi_devices.
I wonder if returning FAST_IO_FAIL would be more appropriate here in 
this case, in order to have scsi_eh let the pending I/O bubble up for a 
timely path failover?

-- 
Mit freundlichen Grüßen / Kind regards
Steffen Maier

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