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

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

[Jiale Yao]

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.

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);
@@ -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);
 	if (drv->probe) {
 		ret = drv->probe(dev, dev_id);
 		if (ret != 0)
-- 
2.34.1

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

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] hv/vmbus: NULL dev_id passed to drv->probe() in vmbus_probe() on dynid race
--

commit 3bc8de7f762094d04ea5ef5ada2811cd26424021
Author: Jiale Yao <yaojiale02@163.com>

hv/vmbus: copy dynamic IDs before dropping the lock

This commit copies matching dynamic device IDs into a caller-provided stack
variable while holding drv->dynids.lock so that driver probe callbacks do not
receive a pointer to a dynamic ID entry that was concurrently freed by
remove_id_store().

> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 4692687cdbf3b..96ad0dfaa50ba 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c

[ ... ]

> @@ -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);
>  	if (drv->probe) {
>  		ret = drv->probe(dev, dev_id);
>  		if (ret != 0)

[Severity: High]
What happens if remove_id_store() removes the matching dynamic ID after
vmbus_match() succeeds, but before vmbus_probe() calls hv_vmbus_get_id()?

Since vmbus_match() and vmbus_probe() acquire and release drv->dynids.lock
separately via hv_vmbus_get_id() -> hv_vmbus_dynid_match(), a concurrent
remove_id_store() can delete the matching entry in between:

drivers/hv/vmbus_drv.c:remove_id_store() {
	...
	spin_lock(&drv->dynids.lock);
	list_for_each_entry_safe(dynid, n, &drv->dynids.list, node) {
		struct hv_vmbus_device_id *id = &dynid->id;

		if (guid_equal(&id->guid, &guid)) {
			list_del(&dynid->node);
			kfree(dynid);
			retval = count;
			break;
		}
	}
	spin_unlock(&drv->dynids.lock);
	...
}

When that happens (or if driver_override is cleared between vmbus_match()
and vmbus_probe()), hv_vmbus_get_id() in vmbus_probe() returns NULL, and
vmbus_probe() passes dev_id = NULL to drv->probe(dev, dev_id).

Drivers such as storvsc and hv_util unconditionally dereference dev_id in
their probe callbacks:

drivers/scsi/storvsc_drv.c:storvsc_probe() {
	...
	bool dev_is_ide = dev_id->driver_data == IDE_GUID;
	bool is_fc = dev_id->driver_data == SFC_GUID;
	...
}

drivers/hv/hv_util.c:util_probe() {
	struct hv_util_service *srv =
		(struct hv_util_service *)dev_id->driver_data;
	...
}

And for drivers that do not dereference dev_id (such as uio_hv_generic),
probe will still succeed and bind the device even though the dynamic ID was
already removed.

Should vmbus_probe() check if (!dev_id && !is_hvsock_channel(dev->channel))
and return -ENODEV before calling drv->probe(), similar to how
__pci_device_probe() and usb_probe_interface() handle a removed dynamic ID?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261019085544.1834700-1-yaojiale02@163.com?part=1

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

[Greg Kroah-Hartman]

On Mon, Oct 19, 2026 at 04:55:44PM +0800, Jiale Yao wrote:
> remove_id_store() can free a matching dynamic ID while VMBus is
> preparing to invoke a driver probe.

And how can that be triggered?

> Copy the ID while holding the dynamic ID lock so probe never receives
> a pointer into a freed list entry.

Why is this driver allowed to handle dynamic ids at all?  Is it really
required?  That will taint the kernel so no real workflow requires it,
right?

> Fixes: fc76936d3ea5 ("vmbus: add support for dynamic device id's")

No cc: stable?

> 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;

Shouldn't this be a memcpy() as that's what you are really doing?

> +			spin_unlock(&drv->dynids.lock);

guard() usage instead?

> +			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;

On the stack?

Ok, I guess this would work, but it feels clunky, why doesn't all other
busses have to do this too?

thanks,

greg k-h