tty: n_gsm: fix DM command

n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010.
See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1516
The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to
the newer 27.010 here. Chapter 5.3.3 defines the DM response. There exists
no DM command. However, the current implementation incorrectly sends DM as
command in case of unexpected UIH frames in gsm_queue().
Correct this behavior by always sending DM as response.

Fixes: 99551fa31543 ("tty: n_gsm line discipline")
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220707113223.3685-2-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 1a70e7ae90cc29f299076164904230813dd5630b..90060018928f31a10a4ca39ab7e10a963861599f 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2207,7 +2207,7 @@ static void gsm_queue(struct gsm_mux *gsm)
        case UIH:
        case UIH|PF:
                if (dlci == NULL || dlci->state != DLCI_OPEN) {
-                       gsm_command(gsm, address, DM|PF);
+                       gsm_response(gsm, address, DM|PF);
                        return;
                }
                dlci->data(dlci, gsm->buf, gsm->len);