[PATCH 6.1 0931/1146] mctp: serial: Fix starting value for frame check sequence

Greg Kroah-Hartman
2022-12-28T16:48:59Z

From: Jeremy Kerr <jk@codeconstruct.com.au>

[ Upstream commit 2856a62762c8409e360d4fd452194c8e57ba1058 ]

RFC1662 defines the start state for the crc16 FCS to be 0xffff, but
we're currently starting at zero.

This change uses the correct start state. We're only early in the
adoption for the serial binding, so there aren't yet any other users to
interface to.

Fixes: a0c2ccd9b5ad ("mctp: Add MCTP-over-serial transport binding")
Reported-by: Harsh Tyagi <harshtya@google.com>
Tested-by: Harsh Tyagi <harshtya@google.com>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/mctp/mctp-serial.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/mctp/mctp-serial.c b/drivers/net/mctp/mctp-serial.c
index 7cd103fd34ef..9f9eaf896047 100644
--- a/drivers/net/mctp/mctp-serial.c
+++ b/drivers/net/mctp/mctp-serial.c
@@ -35,6 +35,8 @@
#define BYTE_FRAME 0x7e
#define BYTE_ESC 0x7d

+#define FCS_INIT 0xffff
+
static DEFINE_IDA(mctp_serial_ida);

enum mctp_serial_state {
@@ -123,7 +125,7 @@ static void mctp_serial_tx_work(struct work_struct *work)
buf[2] = dev->txlen;

if (!dev->txpos)
- dev->txfcs = crc_ccitt(0, buf + 1, 2);
+ dev->txfcs = crc_ccitt(FCS_INIT, buf + 1, 2);

txlen = write_chunk(dev, buf + dev->txpos, 3 - dev->txpos);
if (txlen <= 0) {
@@ -303,7 +305,7 @@ static void mctp_serial_push_header(struct mctp_serial *dev, unsigned char c)
case 1:
if (c == MCTP_SERIAL_VERSION) {
dev->rxpos++;
- dev->rxfcs = crc_ccitt_byte(0, c);
+ dev->rxfcs = crc_ccitt_byte(FCS_INIT, c);
} else {
dev->rxstate = STATE_ERR;
}
--
2.35.1