[PATCH v2] usb: typec: ucsi: reject GET_PDOS responses longer than requested

[pip-izony <eeodqql09@gmail.com>]

From: Seungjin Bae <eeodqql09@gmail.com>

In ucsi_get_pdos(), the number of PDOs is derived from the data length
reported in the CCI register, which is provided by the PPM firmware.

The function requests at most UCSI_MAX_PDOS PDOs on the first read and
PDO_MAX_OBJECTS - UCSI_MAX_PDOS on the second, and ucsi_send_command()
only copies that many bytes into the buffer. However, the returned
length is taken from the 8 bit CCI data length field and is not bounded
by the size of the request.

If a malicious PPM reports a larger length, e.g. 0xFF, each
read is counted as 63 PDOs and ucsi_get_pdos() returns up to 126, beyond
PDO_MAX_OBJECTS and the number of PDOs actually read.

ucsi_get_src_pdos() stores this value in con->num_pdos, and
ucsi_psy_get_voltage_max() and ucsi_psy_get_current_max() use it to
index con->src_pdos[con->num_pdos - 1], resulting in an out-of-bounds
read. This happens without any userspace action, since
ucsi_get_src_pdos() calls ucsi_port_psy_changed() and the resulting
uevent reads every property.

Reject such responses in ucsi_read_pdos(), if the PPM reports more data
than was requested, print an error and return -EPROTO, so that the
invalid count is never used.

Fixes: b04e1747fbcc ("usb: typec: ucsi: Register USB Power Delivery Capabilities")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
---
 v1 -> v2: Print an error and fail instead of limiting the count, as suggested
 by Heikki.

 drivers/usb/typec/ucsi/ucsi.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
index bef3f9b71d71..17beec16fe19 100644
--- a/drivers/usb/typec/ucsi/ucsi.c
+++ b/drivers/usb/typec/ucsi/ucsi.c
@@ -862,6 +862,7 @@ static int ucsi_read_pdos(struct ucsi_connector *con,
 			  u32 *pdos, int offset, int num_pdos)
 {
 	struct ucsi *ucsi = con->ucsi;
+	int len = num_pdos * sizeof(u32);
 	u64 command;
 	int ret;
 
@@ -875,11 +876,17 @@ static int ucsi_read_pdos(struct ucsi_connector *con,
 	command |= UCSI_GET_PDOS_PDO_OFFSET(offset);
 	command |= UCSI_GET_PDOS_NUM_PDOS(num_pdos - 1);
 	command |= is_source(role) ? UCSI_GET_PDOS_SRC_PDOS : 0;
-	ret = ucsi_send_command(ucsi, command, pdos + offset,
-				num_pdos * sizeof(u32));
+	ret = ucsi_send_command(ucsi, command, pdos + offset, len);
 	if (ret < 0 && ret != -ETIMEDOUT)
 		dev_err(ucsi->dev, "UCSI_GET_PDOS failed (%d)\n", ret);
 
+	if (ret > len) {
+		dev_err(ucsi->dev,
+			"PPM returned %d bytes of PDOs, but only %d were requested\n",
+			ret, len);
+		return -EPROTO;
+	}
+
 	return ret;
 }
 
-- 
2.43.0