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Date:   Wed, 25 Nov 2020 18:04:09 +0100
From:   Benjamin Block <bblock@linux.ibm.com>
To:     Qinglang Miao <miaoqinglang@huawei.com>
Cc:     Steffen Maier <maier@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-scsi@vger.kernel.org
Subject: Re: [PATCH] scsi: zfcp: fix use-after-free in
 zfcp_sysfs_port_remove_store
Message-ID: <20201125170409.GA8578@t480-pf1aa2c2>
References: <20201120074853.31706-1-miaoqinglang@huawei.com>
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Sender: Benjamin Block <bblock@linux.ibm.com>
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On Fri, Nov 20, 2020 at 03:48:53PM +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: 83d4e1c33d93 ("[SCSI] zfcp: cleanup port sysfs attribute usage")
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
> ---
>  drivers/s390/scsi/zfcp_sysfs.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/s390/scsi/zfcp_sysfs.c b/drivers/s390/scsi/zfcp_sysfs.c
> index 8d9662e8b..06285e452 100644
> --- a/drivers/s390/scsi/zfcp_sysfs.c
> +++ b/drivers/s390/scsi/zfcp_sysfs.c
> @@ -327,8 +327,6 @@ static ssize_t zfcp_sysfs_port_remove_store(struct device *dev,
>  	list_del(&port->list);
>  	write_unlock_irq(&adapter->port_list_lock);
>  
> -	put_device(&port->dev);
> -
>  	zfcp_erp_port_shutdown(port, 0, "syprs_1");
>  	device_unregister(&port->dev);
>   out:

Hmm, the placement of the put_device() is indeed strange, now that I
think about it. But just removing it and then having a dangling
reference also seems wrong - we do get one explicitly in
`zfcp_get_port_by_wwpn()`.

My first thought would be to move it after the `device_unregister()`
call, and before the `out:` label.


-- 
Best Regards, Benjamin Block  / Linux on IBM Z Kernel Development / IBM Systems
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