When a driver is probed through __driver_attach(), the bus' match()
callback is called without the device lock held, thus accessing the
driver_override field without a lock, which can cause a UAF.
Fix this by using the driver-core driver_override infrastructure taking
care of proper locking internally.
Note that calling match() from __driver_attach() without the device lock
held is intentional. [1]
Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [1]
Reported-by: Gui-Dong Han <hanguidong02@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
Fixes: d765edbb301c ("vmbus: add driver_override support")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
drivers/hv/vmbus_drv.c | 36 +++++-------------------------------
include/linux/hyperv.h | 5 -----
2 files changed, 5 insertions(+), 36 deletions(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index bc4fc1951ae1..bc8dfd136f3c 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -541,34 +541,6 @@ static ssize_t device_show(struct device *dev,
}
static DEVICE_ATTR_RO(device);
-static ssize_t driver_override_store(struct device *dev,
- struct device_attribute *attr,
- const char *buf, size_t count)
-{
- struct hv_device *hv_dev = device_to_hv_device(dev);
- int ret;
-
- ret = driver_set_override(dev, &hv_dev->driver_override, buf, count);
- if (ret)
- return ret;
-
- return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct hv_device *hv_dev = device_to_hv_device(dev);
- ssize_t len;
-
- device_lock(dev);
- len = sysfs_emit(buf, "%s\n", hv_dev->driver_override);
- device_unlock(dev);
-
- return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
/* Set up per device attributes in /sys/bus/vmbus/devices/<bus device> */
static struct attribute *vmbus_dev_attrs[] = {
&dev_attr_id.attr,
@@ -599,7 +571,6 @@ static struct attribute *vmbus_dev_attrs[] = {
&dev_attr_channel_vp_mapping.attr,
&dev_attr_vendor.attr,
&dev_attr_device.attr,
- &dev_attr_driver_override.attr,
NULL,
};
@@ -711,9 +682,11 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
{
const guid_t *guid = &dev->dev_type;
const struct hv_vmbus_device_id *id;
+ int ret;
/* When driver_override is set, only bind to the matching driver */
- if (dev->driver_override && strcmp(dev->driver_override, drv->name))
+ ret = device_match_driver_override(&dev->device, &drv->driver);
+ if (ret == 0)
return NULL;
/* Look at the dynamic ids first, before the static ones */
@@ -722,7 +695,7 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
id = hv_vmbus_dev_match(drv->id_table, guid);
/* driver_override will always match, send a dummy id */
- if (!id && dev->driver_override)
+ if (!id && ret > 0)
id = &vmbus_device_null;
return id;
@@ -1024,6 +997,7 @@ static const struct dev_pm_ops vmbus_pm = {
/* The one and only one */
static const struct bus_type hv_bus = {
.name = "vmbus",
+ .driver_override = true,
.match = vmbus_match,
.shutdown = vmbus_shutdown,
.remove = vmbus_remove,
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index dfc516c1c719..bf689d07d750 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1272,11 +1272,6 @@ struct hv_device {
u16 device_id;
struct device device;
- /*
- * Driver name to force a match. Do not set directly, because core
- * frees it. Use driver_set_override() to set or clear it.
- */
- const char *driver_override;
struct vmbus_channel *channel;
struct kset *channels_kset;
--
2.53.0From: Danilo Krummrich <dakr@kernel.org> Sent: Monday, March 23, 2026 5:59 PM
>
In the patch "Subject" line, the prefix for changes for vmbus_drv.c has
historically been "Drivers: hv: vmbus:". It's a mouthful, but has been kept
fairly consistent over time.
> When a driver is probed through __driver_attach(), the bus' match()
> callback is called without the device lock held, thus accessing the
> driver_override field without a lock, which can cause a UAF.
>
> Fix this by using the driver-core driver_override infrastructure taking
> care of proper locking internally.
>
> Note that calling match() from __driver_attach() without the device lock
> held is intentional. [1]
I've tested this patch in a Hyper-V VM with VMBus devices. Did a simple
VMBus driver override, listed the overrides, and then removed the override.
All the right things happened with driver binding, unbind, etc.
Tested-by: Michael Kelley <mhklinux@outlook.com>
Modulo updates to the comments that I've noted below (and the patch
Subject line mentioned above):
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
>
> Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [1]
> Reported-by: Gui-Dong Han <hanguidong02@gmail.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
> Fixes: d765edbb301c ("vmbus: add driver_override support")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
> drivers/hv/vmbus_drv.c | 36 +++++-------------------------------
> include/linux/hyperv.h | 5 -----
> 2 files changed, 5 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index bc4fc1951ae1..bc8dfd136f3c 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
[snip]
>
> @@ -711,9 +682,11 @@ static const struct hv_vmbus_device_id
> *hv_vmbus_get_id(const struct hv_driver *
> {
> const guid_t *guid = &dev->dev_type;
> const struct hv_vmbus_device_id *id;
> + int ret;
>
> /* When driver_override is set, only bind to the matching driver */
This reference to "driver_override" in the comment was originally to the
"driver_override" field in struct hv_device, which has now gone away. Better
wording would be "If a driver override is set, only bind ...."
> - if (dev->driver_override && strcmp(dev->driver_override, drv->name))
> + ret = device_match_driver_override(&dev->device, &drv->driver);
> + if (ret == 0)
> return NULL;
>
> /* Look at the dynamic ids first, before the static ones */
> @@ -722,7 +695,7 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
> id = hv_vmbus_dev_match(drv->id_table, guid);
>
> /* driver_override will always match, send a dummy id */
Again, the reference to "driver_override" no longer makes sense. The
original comment is a bit opaque in its own way. Let me suggest this new
wording:
If there's a matching driver override, this function should succeed. So
return a dummy device ID if no matching ID is found.
> - if (!id && dev->driver_override)
> + if (!id && ret > 0)
> id = &vmbus_device_null;
>
> return id;
> @@ -1024,6 +997,7 @@ static const struct dev_pm_ops vmbus_pm = {
> /* The one and only one */
> static const struct bus_type hv_bus = {
> .name = "vmbus",
> + .driver_override = true,
> .match = vmbus_match,
> .shutdown = vmbus_shutdown,
> .remove = vmbus_remove,
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index dfc516c1c719..bf689d07d750 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1272,11 +1272,6 @@ struct hv_device {
> u16 device_id;
>
> struct device device;
> - /*
> - * Driver name to force a match. Do not set directly, because core
> - * frees it. Use driver_set_override() to set or clear it.
> - */
> - const char *driver_override;
>
> struct vmbus_channel *channel;
> struct kset *channels_kset;
> --
> 2.53.0
>
When a driver is probed through __driver_attach(), the bus' match()
callback is called without the device lock held, thus accessing the
driver_override field without a lock, which can cause a UAF.
Fix this by using the driver-core driver_override infrastructure taking
care of proper locking internally.
Note that calling match() from __driver_attach() without the device lock
held is intentional. [1]
Tested-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [1]
Reported-by: Gui-Dong Han <hanguidong02@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
Fixes: d765edbb301c ("vmbus: add driver_override support")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
Changes in v2:
- Change patch subject and comments according to Michael's suggestion.
---
drivers/hv/vmbus_drv.c | 43 ++++++++++--------------------------------
include/linux/hyperv.h | 5 -----
2 files changed, 10 insertions(+), 38 deletions(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index bc4fc1951ae1..ba7326ec6add 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -541,34 +541,6 @@ static ssize_t device_show(struct device *dev,
}
static DEVICE_ATTR_RO(device);
-static ssize_t driver_override_store(struct device *dev,
- struct device_attribute *attr,
- const char *buf, size_t count)
-{
- struct hv_device *hv_dev = device_to_hv_device(dev);
- int ret;
-
- ret = driver_set_override(dev, &hv_dev->driver_override, buf, count);
- if (ret)
- return ret;
-
- return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
- struct device_attribute *attr, char *buf)
-{
- struct hv_device *hv_dev = device_to_hv_device(dev);
- ssize_t len;
-
- device_lock(dev);
- len = sysfs_emit(buf, "%s\n", hv_dev->driver_override);
- device_unlock(dev);
-
- return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
/* Set up per device attributes in /sys/bus/vmbus/devices/<bus device> */
static struct attribute *vmbus_dev_attrs[] = {
&dev_attr_id.attr,
@@ -599,7 +571,6 @@ static struct attribute *vmbus_dev_attrs[] = {
&dev_attr_channel_vp_mapping.attr,
&dev_attr_vendor.attr,
&dev_attr_device.attr,
- &dev_attr_driver_override.attr,
NULL,
};
@@ -711,9 +682,11 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
{
const guid_t *guid = &dev->dev_type;
const struct hv_vmbus_device_id *id;
+ int ret;
- /* When driver_override is set, only bind to the matching driver */
- if (dev->driver_override && strcmp(dev->driver_override, drv->name))
+ /* If a driver override is set, only bind to the matching driver */
+ ret = device_match_driver_override(&dev->device, &drv->driver);
+ if (ret == 0)
return NULL;
/* Look at the dynamic ids first, before the static ones */
@@ -721,8 +694,11 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
if (!id)
id = hv_vmbus_dev_match(drv->id_table, guid);
- /* driver_override will always match, send a dummy id */
- if (!id && dev->driver_override)
+ /*
+ * If there's a matching driver override, this function should succeed,
+ * thus return a dummy device ID if no matching ID is found.
+ */
+ if (!id && ret > 0)
id = &vmbus_device_null;
return id;
@@ -1024,6 +1000,7 @@ static const struct dev_pm_ops vmbus_pm = {
/* The one and only one */
static const struct bus_type hv_bus = {
.name = "vmbus",
+ .driver_override = true,
.match = vmbus_match,
.shutdown = vmbus_shutdown,
.remove = vmbus_remove,
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index dfc516c1c719..bf689d07d750 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1272,11 +1272,6 @@ struct hv_device {
u16 device_id;
struct device device;
- /*
- * Driver name to force a match. Do not set directly, because core
- * frees it. Use driver_set_override() to set or clear it.
- */
- const char *driver_override;
struct vmbus_channel *channel;
struct kset *channels_kset;
--
2.53.0© 2016 - 2026 Red Hat, Inc.