Re:Re: [PATCH] hv/vmbus: copy dynamic IDs before dropping the lock

["jiale yao" <19888972804@163.com>]

Hi Kameron,

At 2026-10-21 07:30:55, "Kameron Carr" <kameroncarr@linux.microsoft.com> wrote:
>On 10/19/2026 1:55 AM, Jiale Yao wrote:
>> remove_id_store() can free a matching dynamic ID while VMBus is
>> preparing to invoke a driver probe. Copy the ID while holding the
>> dynamic ID lock so probe never receives a pointer into a freed list
>> entry.
>
>Is this the same fix as:
>
>  3ffc4c9690c3 ("PCI: Fix UAF when probe runs concurrent to dyn ID
>  removal")
>  ef8154d8b52d ("usb: fix UAF when probe runs concurrent to
>  dyn ID removal")
>
>If so, consider citing them in the commit message. Also, consider taking
>inspiration from their implementation.

Yes!

>
>Nit: this subsystem typically uses "Drivers: hv: vmbus:" for the subject
>prefix.
Thanks for your review, how about this one
https://lore.kernel.org/all/20261021143323.338146-1-yaojiale02@163.com/

>
>
>> Fixes: fc76936d3ea5 ("vmbus: add support for dynamic device id's")
>> Signed-off-by: Jiale Yao <yaojiale02@163.com>
>> ---
>>  drivers/hv/vmbus_drv.c | 25 +++++++++++++++----------
>>  1 file changed, 15 insertions(+), 10 deletions(-)
>> 
>> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
>> index 4692687cdbf3..96ad0dfaa50b 100644
>> --- a/drivers/hv/vmbus_drv.c
>> +++ b/drivers/hv/vmbus_drv.c
>> @@ -661,21 +661,22 @@ hv_vmbus_dev_match(const struct hv_vmbus_device_id *id, const guid_t *guid)
>>  }
>>  
>>  static const struct hv_vmbus_device_id *
>> -hv_vmbus_dynid_match(struct hv_driver *drv, const guid_t *guid)
>> +hv_vmbus_dynid_match(struct hv_driver *drv, const guid_t *guid,
>> +		     struct hv_vmbus_device_id *id_copy)
>>  {
>> -	const struct hv_vmbus_device_id *id = NULL;
>>  	struct vmbus_dynid *dynid;
>>  
>>  	spin_lock(&drv->dynids.lock);
>>  	list_for_each_entry(dynid, &drv->dynids.list, node) {
>>  		if (guid_equal(&dynid->id.guid, guid)) {
>> -			id = &dynid->id;
>> -			break;
>> +			*id_copy = dynid->id;
>> +			spin_unlock(&drv->dynids.lock);
>> +			return id_copy;
>>  		}
>>  	}
>>  	spin_unlock(&drv->dynids.lock);
>>  
>> -	return id;
>> +	return NULL;
>>  }
>>  
>>  static const struct hv_vmbus_device_id vmbus_device_null;
>> @@ -685,7 +686,8 @@ static const struct hv_vmbus_device_id vmbus_device_null;
>>   * If there is no match, return NULL.
>>   */
>>  static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *drv,
>> -							struct hv_device *dev)
>> +							struct hv_device *dev,
>> +							struct hv_vmbus_device_id *id_copy)
>>  {
>>  	const guid_t *guid = &dev->dev_type;
>>  	const struct hv_vmbus_device_id *id;
>> @@ -697,7 +699,7 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
>>  		return NULL;
>>  
>>  	/* Look at the dynamic ids first, before the static ones */
>> -	id = hv_vmbus_dynid_match((struct hv_driver *)drv, guid);
>> +	id = hv_vmbus_dynid_match((struct hv_driver *)drv, guid, id_copy);
>>  	if (!id)
>>  		id = hv_vmbus_dev_match(drv->id_table, guid);
>>  
>> @@ -773,6 +775,7 @@ static ssize_t new_id_store(struct device_driver *driver, const char *buf,
>>  			    size_t count)
>>  {
>>  	struct hv_driver *drv = drv_to_hv_drv(driver);
>> +	struct hv_vmbus_device_id id_copy;
>>  	guid_t guid;
>>  	ssize_t retval;
>>  
>> @@ -780,7 +783,7 @@ static ssize_t new_id_store(struct device_driver *driver, const char *buf,
>>  	if (retval)
>>  		return retval;
>>  
>> -	if (hv_vmbus_dynid_match(drv, &guid))
>> +	if (hv_vmbus_dynid_match(drv, &guid, &id_copy))
>>  		return -EEXIST;
>>  
>>  	retval = vmbus_add_dynid(drv, &guid);
>
>This check and the list_add_tail() in vmbus_add_dynid() run in separate
>critical sections, so two concurrent writers can both add the same GUID.
>Consider a preparatory patch that moves the check into vmbus_add_dynid()
>under the same dynids.lock; see 04fde70f782b ("PCI: Fix dyn_id add
>TOCTOU"). new_id_store() then no longer needs hv_vmbus_dynid_match() or
>id_copy at all.
>
>> @@ -840,12 +843,13 @@ static int vmbus_match(struct device *device, const struct device_driver *driver
>>  {
>>  	const struct hv_driver *drv = drv_to_hv_drv(driver);
>>  	struct hv_device *hv_dev = device_to_hv_device(device);
>> +	struct hv_vmbus_device_id id_copy;
>>  
>>  	/* The hv_sock driver handles all hv_sock offers. */
>>  	if (is_hvsock_channel(hv_dev->channel))
>>  		return drv->hvsock;
>>  
>> -	if (hv_vmbus_get_id(drv, hv_dev))
>> +	if (hv_vmbus_get_id(drv, hv_dev, &id_copy))
>>  		return 1;
>>  
>>  	return 0;
>> @@ -860,9 +864,10 @@ static int vmbus_probe(struct device *child_device)
>>  	struct hv_driver *drv =
>>  			drv_to_hv_drv(child_device->driver);
>>  	struct hv_device *dev = device_to_hv_device(child_device);
>> +	struct hv_vmbus_device_id dev_id_copy;
>>  	const struct hv_vmbus_device_id *dev_id;
>>  
>> -	dev_id = hv_vmbus_get_id(drv, dev);
>> +	dev_id = hv_vmbus_get_id(drv, dev, &dev_id_copy);
>
>Consider documenting in include/linux/hyperv.h that the
>hv_vmbus_device_id is only valid during probe so future drivers don't
>save the pointer (see what PCI and USB fixes did in pci.h and usb.h).
>
>>  	if (drv->probe) {
>>  		ret = drv->probe(dev, dev_id);
>>  		if (ret != 0)
>
>Please review the Sashiko comment.
>
>Regards,
>Kameron