[PATCH v1] power: supply: cros_usbpd: Limit port counts to EC_USB_PD_MAX_PORTS

[Jameson Thies <jthies@google.com>]

Currently the cros_usbpd-charger driver probe iterates based on raw
charger port count returned by the embedded controller. The only check
is against the number of USB PD ports which the embedded controller
also defines. A malicious embedded controller could return an inaccurate
port count (up to 255) resulting in an out of bounds write and
subsequent memory corruption.

Update helper functions in cros_usbpd-charger to limit port counts to
EC_USB_PD_MAX_PORTS.

Fixes: 3af15cfacd1e ("power: supply: cros: add support for dedicated port")
Cc: stable@vger.kernel.org
Signed-off-by: Jameson Thies <jthies@google.com>
---
 drivers/power/supply/cros_usbpd-charger.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/power/supply/cros_usbpd-charger.c b/drivers/power/supply/cros_usbpd-charger.c
index 308e1d4e6dd8..82185ee33fd4 100644
--- a/drivers/power/supply/cros_usbpd-charger.c
+++ b/drivers/power/supply/cros_usbpd-charger.c
@@ -125,6 +125,11 @@ static int cros_usbpd_charger_get_num_ports(struct charger_data *charger)
 	if (ret < 0)
 		return ret;
 
+	if (resp.port_count > EC_USB_PD_MAX_PORTS) {
+		dev_warn(charger->dev, "Charge port count out of bounds\n");
+		return EC_USB_PD_MAX_PORTS;
+	}
+
 	return resp.port_count;
 }
 
@@ -138,6 +143,11 @@ static int cros_usbpd_charger_get_usbpd_num_ports(struct charger_data *charger)
 	if (ret < 0)
 		return ret;
 
+	if (resp.num_ports > EC_USB_PD_MAX_PORTS) {
+		dev_warn(charger->dev, "USB PD port count out of bounds\n");
+		return EC_USB_PD_MAX_PORTS;
+	}
+
 	return resp.num_ports;
 }
 

base-commit: 17376e7311cdec252b61cb1ecec43be61907781b
-- 
2.55.0.229.g6434b31f56-goog