From effa453168a7eeb8a562ff4edc1dbf9067360a61 Mon Sep 17 00:00:00 2001
From: Heiner Kallweit <hkallweit1@gmail.com>
Date: Sun, 7 Nov 2021 22:57:00 +0100
Subject: [PATCH] i2c: i801: Don't silently correct invalid transfer size
Git-commit: effa453168a7eeb8a562ff4edc1dbf9067360a61
Patch-mainline: v5.17-rc1
References: git-fixes

If an invalid block size is provided, reject it instead of silently
changing it to a supported value. Especially critical I see the case of
a write transfer with block length 0. In this case we have no guarantee
that the byte we would write is valid. When silently reducing a read to
32 bytes then we don't return an error and the caller may falsely
assume that we returned the full requested data.

If this change should break any (broken) caller, then I think we should
fix the caller.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/i2c/busses/i2c-i801.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 41446f9cc52d..c87ea470eba9 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -775,6 +775,11 @@ static int i801_block_transaction(struct i801_priv *priv, union i2c_smbus_data *
 	int result = 0;
 	unsigned char hostc;
 
+	if (read_write == I2C_SMBUS_READ && command == I2C_SMBUS_BLOCK_DATA)
+		data->block[0] = I2C_SMBUS_BLOCK_MAX;
+	else if (data->block[0] < 1 || data->block[0] > I2C_SMBUS_BLOCK_MAX)
+		return -EPROTO;
+
 	if (command == I2C_SMBUS_I2C_BLOCK_DATA) {
 		if (read_write == I2C_SMBUS_WRITE) {
 			/* set I2C_EN bit in configuration register */
@@ -788,16 +793,6 @@ static int i801_block_transaction(struct i801_priv *priv, union i2c_smbus_data *
 		}
 	}
 
-	if (read_write == I2C_SMBUS_WRITE
-	 || command == I2C_SMBUS_I2C_BLOCK_DATA) {
-		if (data->block[0] < 1)
-			data->block[0] = 1;
-		if (data->block[0] > I2C_SMBUS_BLOCK_MAX)
-			data->block[0] = I2C_SMBUS_BLOCK_MAX;
-	} else {
-		data->block[0] = 32;	/* max for SMBus block reads */
-	}
-
 	/* Experience has shown that the block buffer can only be used for
 	   SMBus (not I2C) block transactions, even though the datasheet
 	   doesn't mention this limitation. */
-- 
2.31.1