FAILED: patch "[PATCH] HID: mcp2221: clear rxbuf after I2C/SMBus transfer completes" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x db2333f88729c8aae062cb171ed058725ff5c901
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090357-reference-varied-a710@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From db2333f88729c8aae062cb171ed058725ff5c901 Mon Sep 17 00:00:00 2001
From: Jiangshan Yi <[email protected]>
Date: Tue, 28 Jul 2026 21:14:41 +0800
Subject: [PATCH] HID: mcp2221: clear rxbuf after I2C/SMBus transfer completes

mcp_i2c_smbus_read() stores the caller-supplied buffer pointer in mcp->rxbuf for the duration of a transfer but never clears it when the transfer finishes or times out. Once the caller frees or reuses the buffer, mcp->rxbuf becomes a dangling pointer. A delayed or spurious MCP2221_I2C_GET_DATA report can then drive mcp2221_raw_event() to memcpy device data into the freed memory, causing a write use-after-free.

Route all return paths through a single exit point that clears mcp->rxbuf and mcp->rxbuf_size, so that the existing !mcp->rxbuf guard in the raw_event handler can reject any report arriving after the transfer has ended.

index 5c7fc56c7c67..9e03d1f733ff 100644
@@ -343,7 +343,7 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 4);
 	if (ret)
-		return ret;
+		goto out;
 
 	mcp->rxbuf_idx = 0;
 

@@ -365,7 +365,7 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 			} else {
 				usleep_range(980, 1000);
 				mcp_cancel_last_cmd(mcp);
-				return ret;
+				goto out;
 			}
 		} else {
 			retries = 0;

@@ -375,6 +375,10 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 	usleep_range(980, 1000);
 	ret = mcp_chk_last_cmd_status_free_bus(mcp);
 
+out:
+	mcp->rxbuf = NULL;
+	mcp->rxbuf_size = 0;
+
 	return ret;
 }
 

From: Florian Pradines <[email protected]>

[ Upstream commit f097d246677b03db814c5862f368cea341b76a00 ]

mcp2221_raw_event() copies device-supplied data into mcp->rxbuf at offset rxbuf_idx without checking that the copy fits within the destination buffer. A device responding with up to 60 bytes to a small I2C/SMBus read can overflow the buffer.

Add a rxbuf_size field to struct mcp2221, set it alongside rxbuf in mcp_i2c_smbus_read(), and check rxbuf_idx + data[3] <= rxbuf_size before the memcpy.

Stable-dep-of: db2333f88729 ("HID: mcp2221: clear rxbuf after I2C/SMBus transfer completes")

---
 drivers/hid/hid-mcp2221.c | 7 +++++++
 1 file changed, 7 insertions(+)

index e1bd1744bf307..f041e47ffba1e 100644
@@ -93,6 +93,7 @@ struct mcp2221 {
 	u8 *rxbuf;
 	u8 txbuf[64];
 	int rxbuf_idx;
+	int rxbuf_size;
 	int status;
 	u8 cur_i2c_clk_div;
 	struct gpio_chip *gc;

@@ -289,12 +290,14 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 		mcp->txbuf[3] = (u8)(msg->addr << 1);
 		total_len = msg->len;
 		mcp->rxbuf = msg->buf;
+		mcp->rxbuf_size = msg->len;
 	} else {
 		mcp->txbuf[1] = smbus_len;
 		mcp->txbuf[2] = 0;
 		mcp->txbuf[3] = (u8)(smbus_addr << 1);
 		total_len = smbus_len;
 		mcp->rxbuf = smbus_buf;
+		mcp->rxbuf_size = smbus_len;
 	}
 
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 4);

@@ -797,6 +800,10 @@ static int mcp2221_raw_event(struct hid_device *hdev,
 					mcp->status = -EINVAL;
 					break;
 				}
+				if (mcp->rxbuf_idx + data[3] > mcp->rxbuf_size) {
+					mcp->status = -EINVAL;
+					break;
+				}
 				buf = mcp->rxbuf;
 				memcpy(&buf[mcp->rxbuf_idx], &data[4], data[3]);
 				mcp->rxbuf_idx = mcp->rxbuf_idx + data[3];

2.53.0

From: Jiangshan Yi <[email protected]>

[ Upstream commit db2333f88729c8aae062cb171ed058725ff5c901 ]

mcp_i2c_smbus_read() stores the caller-supplied buffer pointer in mcp->rxbuf for the duration of a transfer but never clears it when the transfer finishes or times out. Once the caller frees or reuses the buffer, mcp->rxbuf becomes a dangling pointer. A delayed or spurious MCP2221_I2C_GET_DATA report can then drive mcp2221_raw_event() to memcpy device data into the freed memory, causing a write use-after-free.

Route all return paths through a single exit point that clears mcp->rxbuf and mcp->rxbuf_size, so that the existing !mcp->rxbuf guard in the raw_event handler can reject any report arriving after the transfer has ended.

---
 drivers/hid/hid-mcp2221.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index f041e47ffba1e..2332ce6cf5cc5 100644
@@ -302,7 +302,7 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 4);
 	if (ret)
-		return ret;
+		goto out;
 
 	mcp->rxbuf_idx = 0;
 

@@ -324,7 +324,7 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 			} else {
 				usleep_range(980, 1000);
 				mcp_cancel_last_cmd(mcp);
-				return ret;
+				goto out;
 			}
 		} else {
 			retries = 0;

@@ -334,6 +334,10 @@ static int mcp_i2c_smbus_read(struct mcp2221 *mcp,
 	usleep_range(980, 1000);
 	ret = mcp_chk_last_cmd_status_free_bus(mcp);
 
+out:
+	mcp->rxbuf = NULL;
+	mcp->rxbuf_size = 0;
+
 	return ret;
 }
 

2.53.0