linux-kernel - [PATCH] hid: fix I2C read buffer overflow in raw

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Message-ID: <20250726220931.7126-1-contact@arnaud-lcm.com>
Date: Sat, 26 Jul 2025 23:09:31 +0100
From: Arnaud Lecomte <contact@...aud-lcm.com>
To: Rishi Gupta <gupt21@...il.com>
Cc: Jiri Kosina <jikos@...nel.org>,
	Benjamin Tissoires <bentiss@...nel.org>,
	linux-i2c@...r.kernel.org,
	linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot+52c1a7d3e5b361ccd346@...kaller.appspotmail.com,
	Arnaud Lecomte <contact@...aud-lcm.com>
Subject: [PATCH] hid: fix I2C read buffer overflow in raw_event() for mcp2221

As reported by syzbot, mcp2221_raw_event lacked
validation of incoming I2C read data sizes, risking buffer
overflows in mcp->rxbuf during multi-part transfers.
As highlighted in the DS20005565B spec, p44, we have:
"The number of read-back data bytes to follow in this packet:
from 0 to a maximum of 60 bytes of read-back bytes."
This patch enforces we don't exceed this limit.

Reported-by: syzbot+52c1a7d3e5b361ccd346@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=52c1a7d3e5b361ccd346
Tested-by: syzbot+52c1a7d3e5b361ccd346@...kaller.appspotmail.com
Signed-off-by: Arnaud Lecomte <contact@...aud-lcm.com>
---
 drivers/hid/hid-mcp2221.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
index 0f93c22a479f..83941b916cd6 100644
--- a/drivers/hid/hid-mcp2221.c
+++ b/drivers/hid/hid-mcp2221.c
@@ -814,6 +814,10 @@ static int mcp2221_raw_event(struct hid_device *hdev,
 			}
 			if (data[2] == MCP2221_I2C_READ_COMPL ||
 			    data[2] == MCP2221_I2C_READ_PARTIAL) {
+				if (!mcp->rxbuf || mcp->rxbuf_idx < 0 || data[3] > 60) {
+					mcp->status = -EINVAL;
+					break;
+				}
 				buf = mcp->rxbuf;
 				memcpy(&buf[mcp->rxbuf_idx], &data[4], data[3]);
 				mcp->rxbuf_idx = mcp->rxbuf_idx + data[3];
-- 
2.43.0