[PATCH v3] mfd: mt6360: add boundary check in in mt6360 regmap read/write

[cy_huang <u0084500@gmail.com>]

From: ChiYuan Huang <cy_huang@richtek.com>

Fix the potential risk if virtual bank index is over the maximum.

Refer to the discussion list on mt6370.
https://lore.kernel.org/all/20220914013345.GA5802@cyhuang-hp-elitebook-840-g3.rt/
If not to check the boundary, there is also the same issue on mt6360.

For mt6360 register virtual mapping, the normal range is 0 to 0x3FF.
Below's the backtrace in my experiment to access mt6360 0x400 register
with regmap_raw_read() and regmap_raw_write() function.

1) regmap_raw_read()
Unable to handle kernel execute from non-executable memory at virtual
address ffffffd4940c4c20
pc : platform_bus+0x8/0x2e8
lr : i2c_smbus_xfer+0x60/0x120
Call trace:
 platform_bus+0x8/0x2e8
 i2c_smbus_read_i2c_block_data+0x74/0xc0
 mt6360_regmap_read+0x9c/0x180 [mt6360_core]
 _regmap_raw_read+0xe4/0x278
 regmap_raw_read+0xec/0x240

2) regmap_raw_write()
Unable to handle kernel execute from non-executable memory at virtual
address ffffffe4a0ac4c20
pc : platform_bus+0x8/0x2e8
lr : i2c_smbus_xfer+0x60/0x120
Call trace:
 platform_bus+0x8/0x2e8
 i2c_smbus_write_i2c_block_data+0x84/0xd0
 mt6360_regmap_write+0xa8/0x150 [mt6360_core]
 _regmap_raw_write_impl+0x6e8/0x828
 _regmap_raw_write+0xb4/0x130
 regmap_raw_write+0x74/0xb0

After adding the boundary check, the above two cases can be solved.

Fixes: 3b0850440a06c (mfd: mt6360: Merge different sub-devices I2C read/write)
Cc: stable@vger.kernel.org
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
---
Since v3:
- Add backtrace log to help understanding what the potential risk is.

Since v2:
- Assign i2c bank variable after bank index is already checked.

---
 drivers/mfd/mt6360-core.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/mt6360-core.c b/drivers/mfd/mt6360-core.c
index 6eaa677..d3b32eb 100644
--- a/drivers/mfd/mt6360-core.c
+++ b/drivers/mfd/mt6360-core.c
@@ -402,7 +402,7 @@ static int mt6360_regmap_read(void *context, const void *reg, size_t reg_size,
 	struct mt6360_ddata *ddata = context;
 	u8 bank = *(u8 *)reg;
 	u8 reg_addr = *(u8 *)(reg + 1);
-	struct i2c_client *i2c = ddata->i2c[bank];
+	struct i2c_client *i2c;
 	bool crc_needed = false;
 	u8 *buf;
 	int buf_len = MT6360_ALLOC_READ_SIZE(val_size);
@@ -410,6 +410,11 @@ static int mt6360_regmap_read(void *context, const void *reg, size_t reg_size,
 	u8 crc;
 	int ret;
 
+	if (bank >= MT6360_SLAVE_MAX)
+		return -EINVAL;
+
+	i2c = ddata->i2c[bank];
+
 	if (bank == MT6360_SLAVE_PMIC || bank == MT6360_SLAVE_LDO) {
 		crc_needed = true;
 		ret = mt6360_xlate_pmicldo_addr(&reg_addr, val_size);
@@ -453,13 +458,18 @@ static int mt6360_regmap_write(void *context, const void *val, size_t val_size)
 	struct mt6360_ddata *ddata = context;
 	u8 bank = *(u8 *)val;
 	u8 reg_addr = *(u8 *)(val + 1);
-	struct i2c_client *i2c = ddata->i2c[bank];
+	struct i2c_client *i2c;
 	bool crc_needed = false;
 	u8 *buf;
 	int buf_len = MT6360_ALLOC_WRITE_SIZE(val_size);
 	int write_size = val_size - MT6360_REGMAP_REG_BYTE_SIZE;
 	int ret;
 
+	if (bank >= MT6360_SLAVE_MAX)
+		return -EINVAL;
+
+	i2c = ddata->i2c[bank];
+
 	if (bank == MT6360_SLAVE_PMIC || bank == MT6360_SLAVE_LDO) {
 		crc_needed = true;
 		ret = mt6360_xlate_pmicldo_addr(&reg_addr, val_size - MT6360_REGMAP_REG_BYTE_SIZE);
-- 
2.7.4