[PATCH] mfd: mt6370: Add the overbound check to prevent the null pointer

[cy_huang]

From: ChiYuan Huang <cy_huang at richtek.com>

This potential risk could happen at regmap_raw_read or
regmap_raw_write when accessing the over-bound register address.

Below's the issue reproduce log to access over-bound register with
regmap_raw_read function.

[   41.301385] Hardware name: Raspberry Pi 4 Model B Rev 1.2 (DT)
[   41.307296] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   41.314358] pc : i2c_smbus_xfer+0x58/0x120
[   41.314371] lr : i2c_smbus_read_i2c_block_data+0x74/0xc0
[   41.314376] sp : ffffffc008ceb9a0
[   41.327261] x29: ffffffc008ceb9a0 x28: 0000000000000000 x27: ffffffc008cebb94
[   41.334505] x26: ffffffe529116000 x25: ffffffc008ceba30 x24: 0000000000000008
[   41.334513] x23: 0000000000000000 x22: 0000000000000001 x21: 0000000000000000
[   41.334520] x20: 0000000000000000 x19: ffffff804e1e8010 x18: ffffffe529116538
[   41.348994] x17: 0000000000000000 x16: ffffffe528ae11f0 x15: ffffff804e1be01e
[   41.349002] x14: 0000000000000000 x13: ffffff804e1bd03c x12: 7220303032783020
[   41.370710] x11: 0000000000000000 x10: 000000000000000a x9 : ffffffc008cebb60
[   41.377953] x8 : 0000000000000000 x7 : ffffffe529116538 x6 : ffffffc008ceba30
[   41.385196] x5 : 0000000000000008 x4 : 0000000000000000 x3 : 0000000000000001
[   41.392436] x2 : 0000000000000000 x1 : 0000000000000002 x0 : ffffff804e1e8010
[   41.399677] Call trace:
[   41.402153]  i2c_smbus_xfer+0x58/0x120
[   41.405956]  i2c_smbus_read_i2c_block_data+0x74/0xc0
[   41.410991]  mt6370_regmap_read+0x40/0x60 [mt6370]
[   41.415855]  _regmap_raw_read+0xe4/0x278
[   41.419834]  regmap_raw_read+0xec/0x240
[   41.423721]  rg_bound_show+0xb0/0x120 [mt6370]
[   41.428226]  dev_attr_show+0x3c/0x80
[   41.431851]  sysfs_kf_seq_show+0xc4/0x150
[   41.435916]  kernfs_seq_show+0x48/0x60
[   41.439718]  seq_read_iter+0x11c/0x450
[   41.443519]  kernfs_fop_read_iter+0x124/0x1c0
[   41.447937]  vfs_read+0x1a8/0x288
[   41.451296]  ksys_read+0x74/0x100
[   41.454654]  __arm64_sys_read+0x24/0x30
[   41.458541]  invoke_syscall+0x54/0x118
[   41.462344]  el0_svc_common.constprop.4+0x94/0x128
[   41.467202]  do_el0_svc+0x3c/0xd0
[   41.470562]  el0_svc+0x20/0x60
[   41.473658]  el0t_64_sync_handler+0x94/0xb8
[   41.477899]  el0t_64_sync+0x15c/0x160
[   41.481614] Code: 54000388 f9401262 aa1303e0 52800041 (f9400042)
[   41.487793] ---[ end trace 0000000000000000 ]---

Fixes: b2adf788e603 ("mfd: mt6370: Add MediaTek MT6370 support")
Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Signed-off-by: ChiYuan Huang <cy_huang at richtek.com>
---
Hi,

The previous discussion thread can be found here.
https://lore.kernel.org/all/20220914013345.GA5802@cyhuang-hp-elitebook-840-g3.rt/

---
 drivers/mfd/mt6370.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/mfd/mt6370.c b/drivers/mfd/mt6370.c
index cf19cce..acbf960 100644
--- a/drivers/mfd/mt6370.c
+++ b/drivers/mfd/mt6370.c
@@ -190,6 +190,9 @@ static int mt6370_regmap_read(void *context, const void *reg_buf,
 	bank_idx = u8_buf[0];
 	bank_addr = u8_buf[1];
 
+	if (bank_idx >= MT6370_MAX_I2C)
+		return -EINVAL;
+
 	ret = i2c_smbus_read_i2c_block_data(info->i2c[bank_idx], bank_addr,
 					    val_size, val_buf);
 	if (ret < 0)
@@ -211,6 +214,9 @@ static int mt6370_regmap_write(void *context, const void *data, size_t count)
 	bank_idx = u8_buf[0];
 	bank_addr = u8_buf[1];
 
+	if (bank_idx >= MT6370_MAX_I2C)
+		return -EINVAL;
+
 	return i2c_smbus_write_i2c_block_data(info->i2c[bank_idx], bank_addr,
 					      len, data + MT6370_MAX_ADDRLEN);
 }
-- 
2.7.4