linux-kernel - Re: [PATCH] scsi: zfcp: fix use-after-free in zfcp_unit

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Date:   Wed, 25 Nov 2020 18:06:58 +0100
From:   Benjamin Block <bblock@...ux.ibm.com>
To:     Qinglang Miao <miaoqinglang@...wei.com>
Cc:     Steffen Maier <maier@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org
Subject: Re: [PATCH] scsi: zfcp: fix use-after-free in zfcp_unit_remove

On Fri, Nov 20, 2020 at 03:48:54PM +0800, Qinglang Miao wrote:
> kfree(port) is called in put_device(&port->dev) so that following
> use would cause use-after-free bug.
> 
> The former put_device is redundant for device_unregister contains
> put_device already. So just remove it to fix this.
> 
> Fixes: 86bdf218a717 ("[SCSI] zfcp: cleanup unit sysfs attribute usage")
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Qinglang Miao <miaoqinglang@...wei.com>
> ---
>  drivers/s390/scsi/zfcp_unit.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/s390/scsi/zfcp_unit.c b/drivers/s390/scsi/zfcp_unit.c
> index e67bf7388..664b77853 100644
> --- a/drivers/s390/scsi/zfcp_unit.c
> +++ b/drivers/s390/scsi/zfcp_unit.c
> @@ -255,8 +255,6 @@ int zfcp_unit_remove(struct zfcp_port *port, u64 fcp_lun)
>  		scsi_device_put(sdev);
>  	}
>  
> -	put_device(&unit->dev);
> -
>  	device_unregister(&unit->dev);
>  
>  	return 0;

Same as in the other mail for `zfcp_sysfs_port_remove_store()`. We
explicitly get a new ref in `_zfcp_unit_find()`, so we also need to put
that away again.

-- 
Best Regards, Benjamin Block  / Linux on IBM Z Kernel Development / IBM Systems
IBM Deutschland Research & Development GmbH    /    https://www.ibm.com/privacy
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