[PATCH v2] Input: ims-pcu - fix heap-buffer-overflow in ims_pcu_process_data()

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

From: Seungjin Bae <eeodqql09@gmail.com>

The `ims_pcu_process_data()` processes incoming URB data byte by byte.
However, it fails to check if the `read_pos` index exceeds
IMS_PCU_BUF_SIZE.

If a malicious USB device sends a packet larger than IMS_PCU_BUF_SIZE,
`read_pos` will increment indefinitely. Moreover, since `read_pos` is
located immediately after `read_buf`, the attacker can overwrite
`read_pos` itself to arbitrarily control the index.

This manipulated `read_pos` is subsequently used in
`ims_pcu_handle_response()` to copy data into `cmd_buf`, leading to a
heap buffer overflow.

Specifically, an attacker can overwrite the `cmd_done.wait.head` located
at offset 136 relative to `cmd_buf` in the `ims_pcu_handle_response()`.
Consequently, when the driver calls `complete(&pcu->cmd_done)`, it
triggers a control flow hijack by using the manipulated pointer.

Fix this by adding a bounds check for `read_pos` before writing to
`read_buf`. If the packet is too long, discard it, log a warining,
and reset the parser state.

Fixes: 628329d524743 ("Input: add IMS Passenger Control Unit driver")
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
---
 v1 -> v2: Add warning and reset the state of the parser for bad packet

 drivers/input/misc/ims-pcu.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/input/misc/ims-pcu.c b/drivers/input/misc/ims-pcu.c
index 4581f1c53644..c98ef71c841e 100644
--- a/drivers/input/misc/ims-pcu.c
+++ b/drivers/input/misc/ims-pcu.c
@@ -450,6 +450,16 @@ static void ims_pcu_process_data(struct ims_pcu *pcu, struct urb *urb)
 			continue;
 
 		if (pcu->have_dle) {
+			if (pcu->read_pos >= IMS_PCU_BUF_SIZE) {
+				dev_warn(pcu->dev,
+					 "Packet too long (%d bytes), discarding\n",
+					 pcu->read_pos);
+				pcu->have_stx = false;
+				pcu->have_dle = false;
+				pcu->read_pos = 0;
+				continue;
+			}
+
 			pcu->have_dle = false;
 			pcu->read_buf[pcu->read_pos++] = data;
 			pcu->check_sum += data;
@@ -491,6 +501,16 @@ static void ims_pcu_process_data(struct ims_pcu *pcu, struct urb *urb)
 			break;
 
 		default:
+			if (pcu->read_pos >= IMS_PCU_BUF_SIZE) {
+				dev_warn(pcu->dev,
+					 "Packet too long (%d bytes), discarding\n",
+					 pcu->read_pos);
+				pcu->have_stx = false;
+				pcu->have_dle = false;
+				pcu->read_pos = 0;
+				continue;
+			}
+
 			pcu->read_buf[pcu->read_pos++] = data;
 			pcu->check_sum += data;
 			break;
-- 
2.43.0