linux-kernel - Re: [PATCH] scsi: zfcp: Fix a potential double free in zfcp_port

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Message-ID: <20230921102102.GF10864@p1gen4-pw042f0m.fritz.box>
Date:   Thu, 21 Sep 2023 12:21:02 +0200
From:   Benjamin Block <bblock@...ux.ibm.com>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     Steffen Maier <maier@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        James Bottomley <James.Bottomley@...e.de>,
        Christof Schmitt <christof.schmitt@...ibm.com>,
        Swen Schillig <swen@...t.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: zfcp: Fix a potential double free in
 zfcp_port_enqueue

Hello Liu Dinghao,

good find.

On Thu, Sep 21, 2023 at 02:39:15PM +0800, Dinghao Liu wrote:
> When device_register() fails, zfcp_port_release() will be called
> after put_device(). As a result, the zfcp_ccw_adapter_put() after
> err_out is redundant because it will be called in the call-back
> function zfcp_port_release(). Remove it from this error path.

So the reference on the adapter object is doubly put, which may
lead to a premature free of the adapter object itself. Please mention that
either in the subject, or description; it makes it easier to see what exactly
breaks at a glance.

> 
> Fixes: f3450c7b9172 ("[SCSI] zfcp: Replace local reference counting with common kref")
> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> ---
>  drivers/s390/scsi/zfcp_aux.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/scsi/zfcp_aux.c b/drivers/s390/scsi/zfcp_aux.c
> index df782646e856..489e6239dedf 100644
> --- a/drivers/s390/scsi/zfcp_aux.c
> +++ b/drivers/s390/scsi/zfcp_aux.c
> @@ -552,7 +552,7 @@ struct zfcp_port *zfcp_port_enqueue(struct zfcp_adapter *adapter, u64 wwpn,
>  
>  	if (device_register(&port->dev)) {
>  		put_device(&port->dev);
> -		goto err_out;
> +		return ERR_PTR(retval);

I'd rather have a new label at the bottom, in front of the return that is
already there, and jump to that, instead of a different function exit point.

>  	}
>  
>  	write_lock_irq(&adapter->port_list_lock);
> -- 
> 2.17.1
> 

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