[PATCH] i2c: core-smbus: prevent stack corruption on read I2C_BLOCK_DATA

[jeremy.compostella@intel.com (Compostella, Jeremy)]

On a I2C_SMBUS_I2C_BLOCK_DATA read request, if data->block[0] is
greater than I2C_SMBUS_BLOCK_MAX + 1, the underlying I2C driver writes
data out of the msgbuf1 boundary.

It is possible from a user application to run into that issue by call
the I2C_SMBUS ioctl with data.block[0] greater than
I2C_SMBUS_BLOCK_MAX + 1.

Call Trace:
 [<ffffffff8139f695>] dump_stack+0x67/0x92
 [<ffffffff811802a4>] panic+0xc5/0x1eb
 [<ffffffff810ecb5f>] ? vprintk_default+0x1f/0x30
 [<ffffffff817456d3>] ? i2cdev_ioctl_smbus+0x303/0x320
 [<ffffffff8109a68b>] __stack_chk_fail+0x1b/0x20
 [<ffffffff817456d3>] i2cdev_ioctl_smbus+0x303/0x320
 [<ffffffff81745aed>] i2cdev_ioctl+0x4d/0x1e0
 [<ffffffff811f761a>] do_vfs_ioctl+0x2ba/0x490
 [<ffffffff81336e43>] ? security_file_ioctl+0x43/0x60
 [<ffffffff811f7869>] SyS_ioctl+0x79/0x90
 [<ffffffff81a22e97>] entry_SYSCALL_64_fastpath+0x12/0x6a

Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
---
 drivers/i2c/i2c-core-smbus.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 10f00a8..f0be621 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -398,6 +398,12 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
 	case I2C_SMBUS_I2C_BLOCK_DATA:
 		if (read_write == I2C_SMBUS_READ) {
 			msg[1].len = data->block[0];
+			if (msg[1].len > I2C_SMBUS_BLOCK_MAX) {
+				dev_err(&adapter->dev,
+					"Invalid block read size %d\n",
+					data->block[0]);
+				return -EINVAL;
+			}
 		} else {
 			msg[0].len = data->block[0] + 1;
 			if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) {
-- 
2.9.4