linux-kernel - Re: [PATCH] scsi: sg: don't return bogus Sg

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Date:   Wed, 10 May 2017 09:47:00 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Johannes Thumshirn <jthumshirn@...e.de>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Cc:     James Bottomley <jejb@...ux.vnet.ibm.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Linux SCSI Mailinglist <linux-scsi@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Doug Gilbert <dgilbert@...erlog.com>
Subject: Re: [PATCH] scsi: sg: don't return bogus Sg_requests

On 05/10/2017 09:41 AM, Johannes Thumshirn wrote:
> If the list search in sg_get_rq_mark() fails to find a valid request, we
> return a bogus element. This then can later lead to a GPF in sg_remove_scat().
> 
> So don't return bogus Sg_requests in sg_get_rq_mark() but NULL in case the
> list search doesn't find a valid request.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Cc: Hannes Reinecke <hare@...e.de>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Doug Gilbert <dgilbert@...erlog.com>
> ---
>  drivers/scsi/sg.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 0a38ba01b7b4..abfde23fa186 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -2078,7 +2078,7 @@ sg_get_rq_mark(Sg_fd * sfp, int pack_id)
>  		}
>  	}
>  	write_unlock_irqrestore(&sfp->rq_list_lock, iflags);
> -	return resp;
> +	return (resp->done == 2) ? resp : NULL;
>  }
>  
>  /* always adds to end of list */
> 
Not quite.
Please return 'resp' directly from within the loop.
With this fix we run into the risk that by chance the uninitialized
'resp' pointer contains a '2' at the 'done' location, triggering this
issue again.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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