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/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [1]
Reported-by: Gui-Dong Han <hanguidong02@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
Fixes: 5039563e7c25 ("spi: Add driver_override SPI device attribute")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260324005919.2408620-12-dakr@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 7 insertions, 12 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 53dee314d76a..4101c2803eb3 100644
--- a/drivers/spi/spi.c
+++ b/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))