[PATCH] driver core: fix use-after-free of driver_override via driver_match_device()

[Gui-Dong Han <hanguidong02@gmail.com>]

driver_set_override() modifies and frees dev->driver_override while
holding device_lock(dev). However, driver_match_device() reads
dev->driver_override when calling bus match functions.

Currently, driver_match_device() is called from three sites. One site
(__device_attach_driver) holds device_lock(dev), but the other two
(bind_store and __driver_attach) do not. This allows a concurrent
driver_set_override() to free the string while driver_match_device() is
using it, leading to a use-after-free (UAF).

This issue affects at least 11 bus types (including PCI, AMBA, Platform)
that rely on driver_override for matching.

Fix this by holding device_lock(dev) around the driver_match_device() calls
in bind_store() and __driver_attach(). This ensures all access to
dev->driver_override via driver_match_device() is protected by the device
lock.

Tested with the PoCs from Bugzilla that trigger this UAF. Stress testing
the two newly locked paths for 24 hours with CONFIG_PROVE_LOCKING and
CONFIG_LOCKDEP enabled showed no UAF recurrence and no lockdep
warnings.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
Suggested-by: Qiu-ji Chen <chenqiuji666@gmail.com>
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
---
The Bugzilla entry contains full KASAN reports and two PoCs that reliably
reproduce the UAF on both unlocked paths using a standard QEMU setup
(default e1000 device at 0000:00:03.0).
I chose to fix this in the driver core for the following reasons:
1. Both racing functions are part of the driver core.
2. Fixing this per-driver/per-bus is tedious and would require careful
ad-hoc locking that does not align with the existing device_lock(dev).
3. We cannot simply add device_lock(dev) inside bus match functions because
one call path (__device_attach_driver) already holds this lock. Adding the
lock inside the match callback would cause a deadlock on that path.
---
 drivers/base/bus.c | 17 ++++++++++++-----
 drivers/base/dd.c  |  3 +++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 5e75e1bce551..9e62d6009058 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -261,13 +261,20 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf,
 	const struct bus_type *bus = bus_get(drv->bus);
 	struct device *dev;
 	int err = -ENODEV;
+	int ret;
 
 	dev = bus_find_device_by_name(bus, NULL, buf);
-	if (dev && driver_match_device(drv, dev)) {
-		err = device_driver_attach(drv, dev);
-		if (!err) {
-			/* success */
-			err = count;
+	if (dev) {
+		/* Protects against driver_set_override() races */
+		device_lock(dev);
+		ret = driver_match_device(drv, dev);
+		device_unlock(dev);
+		if (ret) {
+			err = device_driver_attach(drv, dev);
+			if (!err) {
+				/* success */
+				err = count;
+			}
 		}
 	}
 	put_device(dev);
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 13ab98e033ea..db60b4500136 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1170,7 +1170,10 @@ static int __driver_attach(struct device *dev, void *data)
 	 * is an error.
 	 */
 
+	/* Protects against driver_set_override() races */
+	device_lock(dev);
 	ret = driver_match_device(drv, dev);
+	device_unlock(dev);
 	if (ret == 0) {
 		/* no match */
 		return 0;
-- 
2.43.0