[PATCH v1 2/2] usb: typec: ucsi: displayport: Check CAM to fix OOB altmode array index

[Jameson Thies <jthies@google.com>]

The UCSI displayport driver indexes the connector's port altmode array
with the GET_CURRENT_CAM response after checking it is not 0xff. The
port altmode array is UCSI_MAX_ALTMODES elements long. If the PPM
returns an invalid GET_CURRENT_CAM response above UCSI_MAX_ALTMODES and
not equal to 0xff, the kernel may crash with an array index OOB error.

Update the UCSI displayport driver to verify the current cam is less
than UCSI_MAX_ALTMODES before accessing the port altmode array. If the
current CAM is greater than UCSI_MAX_ALTMODES and not 0xff, return an
invalid error from ucsi_displayport_enter().

Reviewed-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Andrei Kuchynski <akuchynski@chromium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Jameson Thies <jthies@google.com>
---
 drivers/usb/typec/ucsi/displayport.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
index 7067f2561b84..572da7bbd29c 100644
--- a/drivers/usb/typec/ucsi/displayport.c
+++ b/drivers/usb/typec/ucsi/displayport.c
@@ -71,11 +71,14 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
 	if (ret < 0) {
 		if (ucsi->version > 0x0100)
 			goto err_unlock;
-		cur = 0xff;
 	}
 
 	if (cur != 0xff) {
-		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
+		if (cur < UCSI_MAX_ALTMODES)
+			ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
+		else
+			ret = -EINVAL;
+
 		goto err_unlock;
 	}
 
-- 
2.55.0.1007.g17ff1f9808-goog