linux-kernel - Re: [PATCH v1 03/11] fs/proc/vmcore: disallow vmcore modifications after the vmcore was opened

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Message-ID: <Z0BL/UopaH5Xg5jS@MiWiFi-R3L-srv>
Date: Fri, 22 Nov 2024 17:16:45 +0800
From: Baoquan He <bhe@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
	kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kexec@...ts.infradead.org, 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>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	Thomas Huth <thuth@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>,
	Eric Farman <farman@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 03/11] fs/proc/vmcore: disallow vmcore modifications
 after the vmcore was opened

On 10/25/24 at 05:11pm, David Hildenbrand wrote:
......snip...
> @@ -1482,6 +1470,10 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
>  		return -EINVAL;
>  	}
>  
> +	/* We'll recheck under lock later. */
> +	if (data_race(vmcore_opened))
> +		return -EBUSY;

As I commented to patch 7, if vmcore is opened and closed after
checking, do we need to give up any chance to add device dumping
as below? 

fd = open(/proc/vmcore);
...do checking;
close(fd);

quit any device dump adding;

run makedumpfile on s390;
  ->fd = open(/proc/vmcore);
    -> try to dump;
  ->close(fd);

> +
>  	if (!data || !strlen(data->dump_name) ||
>  	    !data->vmcoredd_callback || !data->size)
>  		return -EINVAL;
> @@ -1515,12 +1507,16 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
>  	dump->buf = buf;
>  	dump->size = data_size;
>  
> -	/* Add the dump to driver sysfs list */
> +	/* Add the dump to driver sysfs list and update the elfcore hdr */
>  	mutex_lock(&vmcore_mutex);
> -	list_add_tail(&dump->list, &vmcoredd_list);
> -	mutex_unlock(&vmcore_mutex);
> +	if (vmcore_opened) {
> +		ret = -EBUSY;
> +		goto out_err;
> +	}
>  
> +	list_add_tail(&dump->list, &vmcoredd_list);
>  	vmcoredd_update_size(data_size);
> +	mutex_unlock(&vmcore_mutex);
>  	return 0;
>  
>  out_err:
> -- 
> 2.46.1
>