xen/xenbus: handle potential dangling pointer issue in xen_pcibk_xenbus_probe

[PATCH] xen/xenbus: handle potential dangling pointer issue in xen_pcibk_xenbus_probe

Posted by yskelg@gmail.com 1 year, 5 months ago

From: Yunseong Kim <yskelg@gmail.com>

If 'xen_pcibk_init_devices()' fails. This ensures that 'pdev->xdev' does
not point to 'xdev' when 'pdev' is freed.

Signed-off-by: Yunseong Kim <yskelg@gmail.com>
---
 drivers/xen/xen-pciback/xenbus.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
index b11e401f1b1e..348d6803b8c0 100644
--- a/drivers/xen/xen-pciback/xenbus.c
+++ b/drivers/xen/xen-pciback/xenbus.c
@@ -54,6 +54,7 @@ static struct xen_pcibk_device *alloc_pdev(struct xenbus_device *xdev)
 	INIT_WORK(&pdev->op_work, xen_pcibk_do_op);
 
 	if (xen_pcibk_init_devices(pdev)) {
+		pdev->xdev = NULL;
 		kfree(pdev);
 		pdev = NULL;
 	}
-- 
2.34.1

Re: [PATCH] xen/xenbus: handle potential dangling pointer issue in xen_pcibk_xenbus_probe

Posted by Jürgen Groß 1 year, 5 months ago

On 29.05.24 14:22, yskelg@gmail.com wrote:
> From: Yunseong Kim <yskelg@gmail.com>
> 
> If 'xen_pcibk_init_devices()' fails. This ensures that 'pdev->xdev' does
> not point to 'xdev' when 'pdev' is freed.
> 
> Signed-off-by: Yunseong Kim <yskelg@gmail.com>
> ---
>   drivers/xen/xen-pciback/xenbus.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
> index b11e401f1b1e..348d6803b8c0 100644
> --- a/drivers/xen/xen-pciback/xenbus.c
> +++ b/drivers/xen/xen-pciback/xenbus.c
> @@ -54,6 +54,7 @@ static struct xen_pcibk_device *alloc_pdev(struct xenbus_device *xdev)
>   	INIT_WORK(&pdev->op_work, xen_pcibk_do_op);
>   
>   	if (xen_pcibk_init_devices(pdev)) {
> +		pdev->xdev = NULL;
>   		kfree(pdev);
>   		pdev = NULL;
>   	}

NAK.

This doesn't make any sense, as pdev is freed.


Juergen

Re: [PATCH] xen/xenbus: handle potential dangling pointer issue in xen_pcibk_xenbus_probe

Posted by Yunseong Kim 1 year, 5 months ago

On 5/29/24 9:27 오후, Jürgen Groß wrote:
> On 29.05.24 14:22, yskelg@gmail.com wrote:
>> From: Yunseong Kim <yskelg@gmail.com>
>>
>> If 'xen_pcibk_init_devices()' fails. This ensures that 'pdev->xdev' does
>> not point to 'xdev' when 'pdev' is freed.
>>
>> Signed-off-by: Yunseong Kim <yskelg@gmail.com>
>> ---
>>   drivers/xen/xen-pciback/xenbus.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/xen/xen-pciback/xenbus.c
>> b/drivers/xen/xen-pciback/xenbus.c
>> index b11e401f1b1e..348d6803b8c0 100644
>> --- a/drivers/xen/xen-pciback/xenbus.c
>> +++ b/drivers/xen/xen-pciback/xenbus.c
>> @@ -54,6 +54,7 @@ static struct xen_pcibk_device *alloc_pdev(struct
>> xenbus_device *xdev)
>>       INIT_WORK(&pdev->op_work, xen_pcibk_do_op);
>>         if (xen_pcibk_init_devices(pdev)) {
>> +        pdev->xdev = NULL;
>>           kfree(pdev);
>>           pdev = NULL;
>>       }
> 
> NAK.
> 
> This doesn't make any sense, as pdev is freed.
> 
> 
> Juergen

Thanks for the code review Juergen!

I don't know if it's a big deal, but I think that if pdev->xdev don't
replace it with NULL, 'struct xenbus_device *xdev' address value stays
in the kmalloc cached memory.

And most of the kernel code I've seen does this (even when it's
'free_pdev()'), so I sent a patch.

In the very unlikely event that. I was thinking if someone look at the
value without initializing the kmalloced memory, someone might see the
'xenbus_device *xdev address'.

Warm Regards,

Yunseong Kim