[PATCH 1/4] Input: psmouse - fix use-after-free during protocol disconnect

When a PS/2 mouse is disconnected or unbound, psmouse_disconnect() calls
the protocol disconnect handler (psmouse->disconnect()). During this time,
stray bytes arriving from the physical controller can still be passed to
psmouse_handle_byte(), which will invoke psmouse->protocol_handler().

This creates an asynchronous race condition with vendor disconnect handlers
(such as synaptics_disconnect()), which free vendor-specific private
structures (psmouse->private). If a byte arrives while the structures
are being freed, it leads to a use-after-free or NULL pointer
dereference in the protocol handler.

Fix this by explicitly setting psmouse->protocol_handler to NULL
safely wrapped in scoped_guard(serio_pause_rx, serio) immediately before
calling the vendor disconnect handler. We also add an unlikely check
in psmouse_handle_byte() to safely drop incoming bytes if the protocol
handler is NULL.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Dmitry Torokhov <[email protected]>
---
 drivers/input/mouse/psmouse-base.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
index 6ab5f1d96eae..916a14b9b6a7 100644
--- a/drivers/input/mouse/psmouse-base.c
+++ b/drivers/input/mouse/psmouse-base.c
@@ -267,7 +267,13 @@ void psmouse_set_state(struct psmouse *psmouse, enum psmouse_state new_state)
  */
 static int psmouse_handle_byte(struct psmouse *psmouse)
 {
-	psmouse_ret_t rc = psmouse->protocol_handler(psmouse);
+	psmouse_ret_t rc;
+
+	/* protocol_handler is NULL when device is being disconnected */
+	if (unlikely(!psmouse->protocol_handler))
+		return 0;
+
+	rc = psmouse->protocol_handler(psmouse);
 
 	switch (rc) {
 	case PSMOUSE_BAD_DATA:
@@ -1466,6 +1472,9 @@ static void psmouse_disconnect(struct serio *serio)
 		psmouse_deactivate(parent);
 	}
 
+	scoped_guard(serio_pause_rx, serio)
+		psmouse->protocol_handler = NULL;
+
 	if (psmouse->disconnect)
 		psmouse->disconnect(psmouse);
 
-- 
2.55.0.229.g6434b31f56-goog