[PATCH 02/12] bus: fsl-mc: use generic driver_override infrastructure

Danilo Krummrich
2026-03-24T00:59:51Z

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: 1f86a00c1159 ("bus/fsl-mc: add support for 'driver_override' in the mc-bus")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
drivers/bus/fsl-mc/fsl-mc-bus.c | 43 +++++--------------------------
drivers/vfio/fsl-mc/vfio_fsl_mc.c | 4 +--
include/linux/fsl/mc.h | 4 ---
3 files changed, 8 insertions(+), 43 deletions(-)

diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
index c117745cf206..221146e4860b 100644
--- a/drivers/bus/fsl-mc/fsl-mc-bus.c
+++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
@@ -86,12 +86,16 @@ static int fsl_mc_bus_match(struct device *dev, const struct device_driver *drv)
struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
const struct fsl_mc_driver *mc_drv = to_fsl_mc_driver(drv);
bool found = false;
+ int ret;

/* When driver_override is set, only bind to the matching driver */
- if (mc_dev->driver_override) {
- found = !strcmp(mc_dev->driver_override, mc_drv->driver.name);
+ ret = device_match_driver_override(dev, drv);
+ if (ret > 0) {
+ found = true;
goto out;
}
+ if (ret == 0)
+ goto out;

if (!mc_drv->match_id_table)
goto out;
@@ -210,39 +214,8 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
}
static DEVICE_ATTR_RO(modalias);

-static ssize_t driver_override_store(struct device *dev,
- struct device_attribute *attr,
- const char *buf, size_t count)
-{
- struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
- int ret;
-
- if (WARN_ON(dev->bus != &fsl_mc_bus_type))
- return -EINVAL;
-
- ret = driver_set_override(dev, &mc_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 fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
- ssize_t len;
-
- device_lock(dev);
- len = sysfs_emit(buf, "%s\n", mc_dev->driver_override);
- device_unlock(dev);
- return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
static struct attribute *fsl_mc_dev_attrs[] = {
&dev_attr_modalias.attr,
- &dev_attr_driver_override.attr,
NULL,
};

@@ -345,6 +318,7 @@ ATTRIBUTE_GROUPS(fsl_mc_bus);

const struct bus_type fsl_mc_bus_type = {
.name = "fsl-mc",
+ .driver_override = true,
.match = fsl_mc_bus_match,
.uevent = fsl_mc_bus_uevent,
.probe = fsl_mc_probe,
@@ -910,9 +884,6 @@ static struct notifier_block fsl_mc_nb;
*/
void fsl_mc_device_remove(struct fsl_mc_device *mc_dev)
{
- kfree(mc_dev->driver_override);
- mc_dev->driver_override = NULL;
-
/*
* The device-specific remove callback will get invoked by device_del()
*/
diff --git a/drivers/vfio/fsl-mc/vfio_fsl_mc.c b/drivers/vfio/fsl-mc/vfio_fsl_mc.c
index 462fae1aa538..b4c3958201b2 100644
--- a/drivers/vfio/fsl-mc/vfio_fsl_mc.c
+++ b/drivers/vfio/fsl-mc/vfio_fsl_mc.c
@@ -424,9 +424,7 @@ static int vfio_fsl_mc_bus_notifier(struct notifier_block *nb,

if (action == BUS_NOTIFY_ADD_DEVICE &&
vdev->mc_dev == mc_cont) {
- mc_dev->driver_override = kasprintf(GFP_KERNEL, "%s",
- vfio_fsl_mc_ops.name);
- if (!mc_dev->driver_override)
+ if (device_set_driver_override(dev, vfio_fsl_mc_ops.name))
dev_warn(dev, "VFIO_FSL_MC: Setting driver override for device in dprc %s failed\n",
dev_name(&mc_cont->dev));
else
diff --git a/include/linux/fsl/mc.h b/include/linux/fsl/mc.h
index 897d6211c163..1da63f2d7040 100644
--- a/include/linux/fsl/mc.h
+++ b/include/linux/fsl/mc.h
@@ -178,9 +178,6 @@ struct fsl_mc_obj_desc {
* @regions: pointer to array of MMIO region entries
* @irqs: pointer to array of pointers to interrupts allocated to this device
* @resource: generic resource associated with this MC object device, if any.
- * @driver_override: driver name to force a match; do not set directly,
- * because core frees it; use driver_set_override() to
- * set or clear it.
*
* Generic device object for MC object devices that are "attached" to a
* MC bus.
@@ -214,7 +211,6 @@ struct fsl_mc_device {
struct fsl_mc_device_irq **irqs;
struct fsl_mc_resource *resource;
struct device_link *consumer_link;
- const char *driver_override;
};

#define to_fsl_mc_device(_dev) \
--
2.53.0