[PATCH v2 1/1] scsi: fc: check for rport presence in fc_block_scsi_eh

[PATCH v2 1/1] scsi: fc: check for rport presence in fc_block_scsi_eh

[Johannes Thumshirn]

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@suse.de>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.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;
+
 	return fc_block_rport(rport);
 }
 EXPORT_SYMBOL(fc_block_scsi_eh);
-- 
2.13.5

Re: [PATCH v2 1/1] scsi: fc: check for rport presence in fc_block_scsi_eh

[Hannes Reinecke]

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@suse.de>
> Reviewed-by: Bart Van Assche <bart.vanassche@wdc.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;
> +
>  	return fc_block_rport(rport);
>  }
>  EXPORT_SYMBOL(fc_block_scsi_eh);
> 
Reviewed-by: Hannes Reinecke <hare@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

Re: [PATCH v2 1/1] scsi: fc: check for rport presence in fc_block_scsi_eh

[Steffen Maier]

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@suse.de>
> Reviewed-by: Bart Van Assche <bart.vanassche@wdc.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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