tty/n_gsm: fix a bug in gsm_dlci_data_output (adaption = 2 case)

in adaption=2 case we should put 1 or 2 byte with modem status bits
at the beginning of a buffer pointed by "dp". n_gsm use 1 byte case,
so it allocate a buffer of len + 1 size. As result we should:
  * put 1 byte of modem status bits
  * increase data pointer
  * put "len" bytes of data
but actually we have:
  * increase first byte with the value of modem status bits
  * decrease "len"
  * put orig_len - 1 bytes of data starting from the buffer beggining
This is evidently wrong.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 1 insertions, 2 deletions

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index da3b31a98654..14c26cdd8aca 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -833,8 +833,7 @@ static int gsm_dlci_data_output(struct gsm_mux *gsm, struct gsm_dlci *dlci)
                 break;
         case 2: /* Unstructed with modem bits. Always one byte as we never
                    send inline break data */
-                *dp += gsm_encode_modem(dlci);
-                len--;
+                *dp++ = gsm_encode_modem(dlci);
                 break;
         }
         WARN_ON(kfifo_out_locked(dlci->fifo, dp , len, &dlci->lock) != len);