[PATCH 27/28] i2c: cgbc: Propagate hardware errors when polling read status

[Lee Jones <lee@kernel.org>]

In cgbc_i2c_xfer_msg(), read_poll_timeout() uses the same ret variable
to store the polled return value of cgbc_i2c_get_status() and the
timeout result of the macro itself.  When cgbc_i2c_get_status() returns
a negative error code (such as -EIO on an I2C NACK), the loop condition
ret != CGBC_I2C_STAT_BUSY evaluates to true and read_poll_timeout()
overwrites ret with 0.  The driver then issues CGBC_I2C_CMD_DATA, which
completes with CGBC_STATUS_CMD_READY without populating msg->buf,
leaving uninitialised heap memory in the caller's read buffer.

Store the polled status in a separate variable, verify that it equals
CGBC_I2C_STAT_DAT, and check that CGBC_I2C_CMD_DATA returns the expected
number of bytes.

Fixes: 6894f640b8f3 ("i2c: Congatec Board Controller i2c bus driver")
Closes: https://sashiko.dev/#/bug/linux-66cbf4b1-a219-4012-969d-236417bf419a
Cc: stable@vger.kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>
---
 drivers/i2c/busses/i2c-cgbc.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-cgbc.c b/drivers/i2c/busses/i2c-cgbc.c
index 25a74fa51aa0..9909c25f0b18 100644
--- a/drivers/i2c/busses/i2c-cgbc.c
+++ b/drivers/i2c/busses/i2c-cgbc.c
@@ -205,9 +205,9 @@ static int cgbc_i2c_xfer_msg(struct i2c_adapter *adap)
 	struct cgbc_device_data *cgbc = i2c->cgbc;
 	struct i2c_msg *msg = i2c->msg;
 	u8 cmd[CGBC_I2C_CMD_SIZE];
-	int ret, max_len, len, i;
+	int ret, status, max_len, len, i;
 	unsigned int cmd_len;
-	u8 cmd_data;
+	u8 cmd_data, data_len;
 
 	struct cgbc_i2c_transfer xfer = {
 		.bus_id = algo_data->bus_id,
@@ -266,17 +266,32 @@ static int cgbc_i2c_xfer_msg(struct i2c_adapter *adap)
 		if (ret)
 			goto err;
 
-		ret = read_poll_timeout(cgbc_i2c_get_status, ret,
-					ret != CGBC_I2C_STAT_BUSY, 0,
+		ret = read_poll_timeout(cgbc_i2c_get_status, status,
+					status != CGBC_I2C_STAT_BUSY, 0,
 					2 * algo_data->read_maxtime_us, false, adap);
-		if (ret < 0)
+		if (ret)
 			goto err;
 
+		if (status < 0) {
+			ret = status;
+			goto err;
+		}
+
+		if (status != CGBC_I2C_STAT_DAT) {
+			ret = -EIO;
+			goto err;
+		}
+
 		cmd_data = CGBC_I2C_CMD_DATA | algo_data->bus_id;
 		ret = cgbc_command(cgbc, &cmd_data, sizeof(cmd_data),
-				   msg->buf + i2c->pos, len, NULL);
+				   msg->buf + i2c->pos, len, &data_len);
 		if (ret)
 			goto err;
+
+		if (data_len != len) {
+			ret = -EIO;
+			goto err;
+		}
 	}
 
 	if (len == (msg->len - i2c->pos)) {
-- 
2.56.0.218.g1ec904b173-goog