[PATCH 1/8] usb: typec: wcove: don't write past struct pd_message in wcove_read_rx_buffer()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

wcove_read_rx_buffer() copies the PD RX FIFO into the caller's
struct pd_message with

	for (i = 0; i < USBC_RXINFO_RXBYTES(info); i++)
		regmap_read(wcove->regmap, USBC_RX_DATA + i, msg + i);

which has two problems:

USBC_RXINFO_RXBYTES() is a 5-bit field (max 31) while struct pd_message
is 30 bytes (__le16 header + __le32 payload[PD_MAX_PAYLOAD], packed).
The byte count latched in RXINFO is the number of bytes the port partner
put on the wire, so a malicious partner that transmits a 31-byte frame
can drive the loop one byte past the destination if the WCOVE BMC
receiver does not enforce the PD object-count limit in hardware. The
existing FIXME flagged this as unverified.

Independently, regmap_read() takes an unsigned int * and stores a full
unsigned int at the destination. Passing the byte pointer msg + i means
each iteration writes four bytes; the high three are zero (val_bits is
8) and are normally overwritten by the next iteration, but the final
iteration's high bytes are not. With RXBYTES == 30 the i == 29 iteration
already writes three zero bytes past msg, which sits on the IRQ thread's
stack in wcove_typec_irq().

Clamp the loop to sizeof(struct pd_message) and read each register into
a local before storing only its low byte, so the copy can never exceed
the destination regardless of what RXINFO reports.

Assisted-by: gkh_clanker_t1000
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/usb/typec/tcpm/wcove.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/typec/tcpm/wcove.c b/drivers/usb/typec/tcpm/wcove.c
index 759c982bb16a..0e5a3e277c3e 100644
--- a/drivers/usb/typec/tcpm/wcove.c
+++ b/drivers/usb/typec/tcpm/wcove.c
@@ -444,9 +444,11 @@ static int wcove_start_toggling(struct tcpc_dev *tcpc,
 	return regmap_write(wcove->regmap, USBC_CONTROL1, usbc_ctrl);
 }
 
-static int wcove_read_rx_buffer(struct wcove_typec *wcove, void *msg)
+static int wcove_read_rx_buffer(struct wcove_typec *wcove,
+				struct pd_message *msg)
 {
-	unsigned int info;
+	unsigned int info, val, len;
+	u8 *buf = (u8 *)msg;
 	int ret;
 	int i;
 
@@ -454,12 +456,13 @@ static int wcove_read_rx_buffer(struct wcove_typec *wcove, void *msg)
 	if (ret)
 		return ret;
 
-	/* FIXME: Check that USBC_RXINFO_RXBYTES(info) matches the header */
+	len = min(USBC_RXINFO_RXBYTES(info), sizeof(*msg));
 
-	for (i = 0; i < USBC_RXINFO_RXBYTES(info); i++) {
-		ret = regmap_read(wcove->regmap, USBC_RX_DATA + i, msg + i);
+	for (i = 0; i < len; i++) {
+		ret = regmap_read(wcove->regmap, USBC_RX_DATA + i, &val);
 		if (ret)
 			return ret;
+		buf[i] = val;
 	}
 
 	return regmap_write(wcove->regmap, USBC_RXSTATUS,
-- 
2.54.0