[PATCH v2] usb: typec: ucsi: displayport: 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.

Fixes: af8622f6a585 ("usb: typec: ucsi: Support for DisplayPort alt mode")
Cc: stable@vger.kernel.org
Signed-off-by: Jameson Thies <jthies@google.com>
---
Changes in v2:
 - removed 0xff alt mode assignement when GET_CURRENT_CAM returns an error.
 - return -EINVAL when alt mode index above UCSI_MAX_ALTMODES is returned.

 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;
 	}
 

base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
-- 
2.55.0.979.g7e5102b832-goog