[PATCH] scsi: zero per-cmd driver data for each MQ I/O

[PATCH] scsi: zero per-cmd driver data for each MQ I/O

[Long Li]

From: Long Li <longli@microsoft.com>

Lower layer driver may not initialize private data before use. Zero them
out to prevent use of stale data.

Signed-off-by: Long Li <longli@microsoft.com>
---
 drivers/scsi/scsi_lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 19125d7..a821593 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1850,7 +1850,7 @@ static int scsi_mq_prep_fn(struct request *req)
 
 	/* zero out the cmd, except for the embedded scsi_request */
 	memset((char *)cmd + sizeof(cmd->req), 0,
-		sizeof(*cmd) - sizeof(cmd->req));
+		sizeof(*cmd) - sizeof(cmd->req) + shost->hostt->cmd_size);
 
 	req->special = cmd;
 
-- 
2.7.4

RE: [PATCH] scsi: zero per-cmd driver data for each MQ I/O

[Long Li]

> -----Original Message-----
> From: Long Li [mailto:longli@exchange.microsoft.com]
> Sent: Wednesday, May 10, 2017 2:07 PM
> To: James E.J. Bottomley <jejb@linux.vnet.ibm.com>; Martin K. Petersen
> <martin.petersen@oracle.com>; linux-scsi@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Cc: Long Li <longli@microsoft.com>
> Subject: [PATCH] scsi: zero per-cmd driver data for each MQ I/O
> 
> From: Long Li <longli@microsoft.com>
> 
> Lower layer driver may not initialize private data before use. Zero them out
> to prevent use of stale data.
> 
> Signed-off-by: Long Li <longli@microsoft.com>

Can someone help review this patch?

> ---
>  drivers/scsi/scsi_lib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index
> 19125d7..a821593 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1850,7 +1850,7 @@ static int scsi_mq_prep_fn(struct request *req)
> 
>         /* zero out the cmd, except for the embedded scsi_request */
>         memset((char *)cmd + sizeof(cmd->req), 0,
> -               sizeof(*cmd) - sizeof(cmd->req));
> +               sizeof(*cmd) - sizeof(cmd->req) +
> + shost->hostt->cmd_size);
> 
>         req->special = cmd;
> 
> --
> 2.7.4

Re: [Possible Phish Fraud][PATCH] scsi: zero per-cmd driver data for each MQ I/O

[Bart Van Assche]

On Wed, 2017-05-10 at 14:07 -0700, Long Li wrote:
> From: Long Li <longli@microsoft.com>
> 
> Lower layer driver may not initialize private data before use. Zero them
> out to prevent use of stale data.
> 
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
>  drivers/scsi/scsi_lib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 19125d7..a821593 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1850,7 +1850,7 @@ static int scsi_mq_prep_fn(struct request *req)
>  
>  	/* zero out the cmd, except for the embedded scsi_request */
>  	memset((char *)cmd + sizeof(cmd->req), 0,
> -		sizeof(*cmd) - sizeof(cmd->req));
> +		sizeof(*cmd) - sizeof(cmd->req) + shost->hostt->cmd_size);
>  
>  	req->special = cmd;

Hello Long,

Sorry but this patch looks wrong to me. Since scsi_mq_prep_fn() is called
after scsi_req_init(), erasing struct scsi_request from scsi_mq_prep_fn()
will erase the values that were set by scsi_req_init(). That includes
information like the pointer to the SCSI CDB and the CDB itself. See e.g.
scsi_execute().

Did you come up with this patch after source reading or did you come up
with this patch while chasing a bug?

Thanks,

Bart. 

RE: [PATCH] scsi: zero per-cmd driver data for each MQ I/O

[KY Srinivasan]

> -----Original Message-----
> From: Long Li
> Sent: Monday, May 15, 2017 3:48 PM
> To: Long Li <longli@microsoft.com>; James E.J. Bottomley
> <jejb@linux.vnet.ibm.com>; Martin K. Petersen
> <martin.petersen@oracle.com>; linux-scsi@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Cc: KY Srinivasan <kys@microsoft.com>; Stephen Hemminger
> <sthemmin@microsoft.com>
> Subject: RE: [PATCH] scsi: zero per-cmd driver data for each MQ I/O
> 
> > -----Original Message-----
> > From: Long Li [mailto:longli@exchange.microsoft.com]
> > Sent: Wednesday, May 10, 2017 2:07 PM
> > To: James E.J. Bottomley <jejb@linux.vnet.ibm.com>; Martin K. Petersen
> > <martin.petersen@oracle.com>; linux-scsi@vger.kernel.org; linux-
> > kernel@vger.kernel.org
> > Cc: Long Li <longli@microsoft.com>
> > Subject: [PATCH] scsi: zero per-cmd driver data for each MQ I/O
> >
> > From: Long Li <longli@microsoft.com>
> >
> > Lower layer driver may not initialize private data before use. Zero them out
> > to prevent use of stale data.
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> 
> Can someone help review this patch?
Reviewed-by:  K. Y. Srinivasan <kys@microsoft.com>

> 
> > ---
> >  drivers/scsi/scsi_lib.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index
> > 19125d7..a821593 100644
> > --- a/drivers/scsi/scsi_lib.c
> > +++ b/drivers/scsi/scsi_lib.c
> > @@ -1850,7 +1850,7 @@ static int scsi_mq_prep_fn(struct request *req)
> >
> >         /* zero out the cmd, except for the embedded scsi_request */
> >         memset((char *)cmd + sizeof(cmd->req), 0,
> > -               sizeof(*cmd) - sizeof(cmd->req));
> > +               sizeof(*cmd) - sizeof(cmd->req) +
> > + shost->hostt->cmd_size);
> >
> >         req->special = cmd;
> >
> > --
> > 2.7.4

Re: [PATCH] scsi: zero per-cmd driver data for each MQ I/O

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>