[PATCH] net: wwan: t7xx: validate control-message data_length against the skb

[Doruk Tan Ozturk <doruk@0sec.ai>]

control_msg_handler() handles a CTL_ID_HS2_MSG control message by pulling
the ctrl_msg_header and passing the modem-supplied data_length as the
length of the handshake-2 payload to t7xx_fsm_append_event():

	ret = t7xx_fsm_append_event(ctl, event, skb->data,
				    le32_to_cpu(ctrl_msg_h->data_length));

data_length is a device-controlled __le32 that is never bounded against
the actual received payload (skb->len after the pull).
t7xx_fsm_append_event() then does memcpy(event->data, data, length) with
skb->data as the source, so a data_length larger than the payload reads
out of bounds past the control skb (the destination is sized to length,
so only the source over-reads). A compromised or malfunctioning modem can
trigger it during the bring-up handshake; both the modem and AP control
ports reach the same call site.

Reject a data_length that exceeds the received payload.

Found by 0sec (https://0sec.ai) using automated source analysis; the
missing bound is evident from source. Compile-tested.

Fixes: da45d2566a1d ("net: wwan: t7xx: Add control port")
Cc: stable@vger.kernel.org
Assisted-by: 0sec:claude-opus-4-8
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
---
 drivers/net/wwan/t7xx/t7xx_port_ctrl_msg.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wwan/t7xx/t7xx_port_ctrl_msg.c b/drivers/net/wwan/t7xx/t7xx_port_ctrl_msg.c
index f869e4ed9ee9..871ed63d3c4d 100644
--- a/drivers/net/wwan/t7xx/t7xx_port_ctrl_msg.c
+++ b/drivers/net/wwan/t7xx/t7xx_port_ctrl_msg.c
@@ -186,10 +186,15 @@ static int control_msg_handler(struct t7xx_port *port, struct sk_buff *skb)
 			int event = port_conf->rx_ch == PORT_CH_CONTROL_RX ?
 				    FSM_EVENT_MD_HS2 : FSM_EVENT_AP_HS2;
 
-			ret = t7xx_fsm_append_event(ctl, event, skb->data,
-						    le32_to_cpu(ctrl_msg_h->data_length));
-			if (ret)
-				dev_err(port->dev, "Failed to append Handshake 2 event");
+			if (le32_to_cpu(ctrl_msg_h->data_length) > skb->len) {
+				dev_err(port->dev, "Invalid Handshake 2 data length\n");
+				ret = -EINVAL;
+			} else {
+				ret = t7xx_fsm_append_event(ctl, event, skb->data,
+							    le32_to_cpu(ctrl_msg_h->data_length));
+				if (ret)
+					dev_err(port->dev, "Failed to append Handshake 2 event");
+			}
 		}
 
 		dev_kfree_skb_any(skb);
-- 
2.43.0