On Tue, Aug 27, 2024 at 10:07:59AM +0800, Matt Johnston wrote:

0x7d and 0x7e bytes are meant to be escaped in the data portion of frames, but this didn't occur since next_chunk_len() had an off-by-one error. That also resulted in the final byte of a payload being written as a separate tty write op.

The chunk prior to an escaped byte would be one byte short, and the next call would never test the txpos+1 case, which is where the escaped byte was located. That meant it never hit the escaping case in mctp_serial_tx_work().

Example Input: 01 00 08 c8 7e 80 02

Previous incorrect chunks from next_chunk_len():

01 00 08 c8 7e 80 02

With this fix:

01 00 08 c8 7e 80 02

Cc: stable@vger.kernel.org Fixes: a0c2ccd9b5ad ("mctp: Add MCTP-over-serial transport binding") Signed-off-by: Matt Johnston matt@codeconstruct.com.au

Reviewed-by: Larysa Zaremba larysa.zaremba@intel.com

---

drivers/net/mctp/mctp-serial.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/mctp/mctp-serial.c b/drivers/net/mctp/mctp-serial.c index d7db11355909..82890e983847 100644 --- a/drivers/net/mctp/mctp-serial.c +++ b/drivers/net/mctp/mctp-serial.c @@ -91,8 +91,8 @@ static int next_chunk_len(struct mctp_serial *dev) * will be those non-escaped bytes, and does not include the escaped * byte. */

• for (i = 1; i + dev->txpos + 1 < dev->txlen; i++) {

• if (needs_escape(dev->txbuf[dev->txpos + i + 1]))
  

• for (i = 1; i + dev->txpos < dev->txlen; i++) {

• if (needs_escape(dev->txbuf[dev->txpos + i]))
  break;
  

  }