[PATCH 4.12 08/27] i2c: ismt: Return EMSGSIZE for block reads with bogus length

[Greg Kroah-Hartman]

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stephen Douthit <stephend@xxxxxxxxxxxxxxxxxx>

commit ba201c4f5ebe13d7819081756378777d8153f23e upstream.

Compare the number of bytes actually seen on the wire to the byte
count field returned by the slave device.

Previously we just overwrote the byte count returned by the slave
with the real byte count and let the caller figure out if the
message was sane.

Signed-off-by: Stephen Douthit <stephend@xxxxxxxxxxxxxxxxxx>
Tested-by: Dan Priamo <danp@xxxxxxxxxxxxxxxxxx>
Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
Signed-off-by: Wolfram Sang <wsa@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/i2c/busses/i2c-ismt.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/i2c/busses/i2c-ismt.c
+++ b/drivers/i2c/busses/i2c-ismt.c
@@ -341,8 +341,10 @@ static int ismt_process_desc(const struc
 			break;
 		case I2C_SMBUS_BLOCK_DATA:
 		case I2C_SMBUS_I2C_BLOCK_DATA:
+			if (desc->rxbytes != dma_buffer[0] + 1)
+				return -EMSGSIZE;
+
 			memcpy(data->block, dma_buffer, desc->rxbytes);
-			data->block[0] = desc->rxbytes - 1;
 			break;
 		}
 		return 0;