linux-kernel - [PATCH 3.16 167/294] i2c: ismt: Don't duplicate the receive length for block reads

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Date:   Mon, 06 Nov 2017 23:03:02 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Dan Priamo" <danp@...engineering.com>,
        "Stephen Douthit" <stephend@...engineering.com>,
        "Neil Horman" <nhorman@...driver.com>,
        "Wolfram Sang" <wsa@...-dreams.de>
Subject: [PATCH 3.16 167/294] i2c: ismt: Don't duplicate the receive
 length for block reads

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Stephen Douthit <stephend@...engineering.com>

commit b6c159a9cb69c2cf0bf59d4e12c3a2da77e4d994 upstream.

According to Table 15-14 of the C2000 EDS (Intel doc #510524) the
rx data pointed to by the descriptor dptr contains the byte count.

desc->rxbytes reports all bytes read on the wire, including the
"byte count" byte.  So if a device sends 4 bytes in response to a
block read, on the wire and in the DMA buffer we see:

count data1 data2 data3 data4
 0x04  0xde  0xad  0xbe  0xef

That's what we want to return in data->block to the next level.

Instead we were actually prefixing that with desc->rxbytes:

bad
count count data1 data2 data3 data4
 0x05  0x04  0xde  0xad  0xbe  0xef

This was discovered while developing a BMC solution relying on the
ipmi_ssif.c driver which was trying to interpret the bogus length
field as part of the IPMI response.

Signed-off-by: Stephen Douthit <stephend@...engineering.com>
Tested-by: Dan Priamo <danp@...engineering.com>
Acked-by: Neil Horman <nhorman@...driver.com>
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/i2c/busses/i2c-ismt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/i2c/busses/i2c-ismt.c
+++ b/drivers/i2c/busses/i2c-ismt.c
@@ -344,8 +344,8 @@ static int ismt_process_desc(const struc
 			break;
 		case I2C_SMBUS_BLOCK_DATA:
 		case I2C_SMBUS_I2C_BLOCK_DATA:
-			memcpy(&data->block[1], dma_buffer, desc->rxbytes);
-			data->block[0] = desc->rxbytes;
+			memcpy(data->block, dma_buffer, desc->rxbytes);
+			data->block[0] = desc->rxbytes - 1;
 			break;
 		}
 		return 0;