spi: use generic driver_override infrastructure

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]

Also note that we do not enable the driver_override feature of struct
bus_type, as SPI - in contrast to most other buses - passes "" to
sysfs_emit() when the driver_override pointer is NULL. Thus, printing
"\n" instead of "(null)\n".

Link: https://lore.kernel.org/driver-core/[email protected]/ [1]
Reported-by: Gui-Dong Han <[email protected]>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
Fixes: 5039563 ("spi: Add driver_override SPI device attribute")
Signed-off-by: Danilo Krummrich <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Mark Brown <[email protected]>

Author: Danilo Krummrich

drivers/spi/spi.c

@@ -50,7 +50,6 @@ static void spidev_release(struct device *dev)
 	struct spi_device	*spi = to_spi_device(dev);
 
 	spi_controller_put(spi->controller);
-	kfree(spi->driver_override);
 	free_percpu(spi->pcpu_statistics);
 	kfree(spi);
 }
@@ -73,10 +72,9 @@ static ssize_t driver_override_store(struct device *dev,
 				     struct device_attribute *a,
 				     const char *buf, size_t count)
 {
-	struct spi_device *spi = to_spi_device(dev);
 	int ret;
 
-	ret = driver_set_override(dev, &spi->driver_override, buf, count);
+	ret = __device_set_driver_override(dev, buf, count);
 	if (ret)
 		return ret;
 
@@ -86,13 +84,8 @@ static ssize_t driver_override_store(struct device *dev,
 static ssize_t driver_override_show(struct device *dev,
 				    struct device_attribute *a, char *buf)
 {
-	const struct spi_device *spi = to_spi_device(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", spi->driver_override ? : "");
-	device_unlock(dev);
-	return len;
+	guard(spinlock)(&dev->driver_override.lock);
+	return sysfs_emit(buf, "%s\n", dev->driver_override.name ?: "");
 }
 static DEVICE_ATTR_RW(driver_override);
 
@@ -376,10 +369,12 @@ static int spi_match_device(struct device *dev, const struct device_driver *drv)
 {
 	const struct spi_device	*spi = to_spi_device(dev);
 	const struct spi_driver	*sdrv = to_spi_driver(drv);
+	int ret;
 
 	/* Check override first, and if set, only use the named driver */
-	if (spi->driver_override)
-		return strcmp(spi->driver_override, drv->name) == 0;
+	ret = device_match_driver_override(dev, drv);
+	if (ret >= 0)
+		return ret;
 
 	/* Attempt an OF style match */
 	if (of_driver_match_device(dev, drv))

include/linux/spi/spi.h

@@ -159,10 +159,6 @@ extern void spi_transfer_cs_change_delay_exec(struct spi_message *msg,
  * @modalias: Name of the driver to use with this device, or an alias
  *	for that name.  This appears in the sysfs "modalias" attribute
  *	for driver coldplugging, and in uevents used for hotplugging
- * @driver_override: If the name of a driver is written to this attribute, then
- *	the device will bind to the named driver and only the named driver.
- *	Do not set directly, because core frees it; use driver_set_override() to
- *	set or clear it.
  * @pcpu_statistics: statistics for the spi_device
  * @word_delay: delay to be inserted between consecutive
  *	words of a transfer
@@ -224,7 +220,6 @@ struct spi_device {
 	void			*controller_state;
 	void			*controller_data;
 	char			modalias[SPI_NAME_SIZE];
-	const char		*driver_override;
 
 	/* The statistics */
 	struct spi_statistics __percpu	*pcpu_statistics;