From: Daniel Starke <daniel.starke@xxxxxxxxxxx> commit 398867f59f956985f4c324f173eff7b946e14bd8 upstream. 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 5.4.6.1 states that each command frame shall be made up from type, length and value. Looking for example in chapter 5.4.6.3.5 at the description for the encoding of a flow control on command it becomes obvious, that the type and length field is always present whereas the value may be zero bytes long. The current implementation omits the length field if the value is not present. This is wrong. Correct this by always sending the length in gsm_control_transmit(). So far only the modem status command (MSC) has included a value and encoded its length directly. Therefore, also change gsmtty_modem_update(). Fixes: e1eaea46bb40 ("tty: n_gsm line discipline") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Daniel Starke <daniel.starke@xxxxxxxxxxx> Link: https://lore.kernel.org/r/20220414094225.4527-12-daniel.starke@xxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/n_gsm.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -1327,11 +1327,12 @@ static void gsm_control_response(struct static void gsm_control_transmit(struct gsm_mux *gsm, struct gsm_control *ctrl) { - struct gsm_msg *msg = gsm_data_alloc(gsm, 0, ctrl->len + 1, gsm->ftype); + struct gsm_msg *msg = gsm_data_alloc(gsm, 0, ctrl->len + 2, gsm->ftype); if (msg == NULL) return; - msg->data[0] = (ctrl->cmd << 1) | 2 | EA; /* command */ - memcpy(msg->data + 1, ctrl->data, ctrl->len); + msg->data[0] = (ctrl->cmd << 1) | CR | EA; /* command */ + msg->data[1] = (ctrl->len << 1) | EA; + memcpy(msg->data + 2, ctrl->data, ctrl->len); gsm_data_queue(gsm->dlci[0], msg); } @@ -2957,19 +2958,17 @@ static struct tty_ldisc_ops tty_ldisc_pa static int gsmtty_modem_update(struct gsm_dlci *dlci, u8 brk) { - u8 modembits[5]; + u8 modembits[3]; struct gsm_control *ctrl; int len = 2; - if (brk) + modembits[0] = (dlci->addr << 2) | 2 | EA; /* DLCI, Valid, EA */ + modembits[1] = (gsm_encode_modem(dlci) << 1) | EA; + if (brk) { + modembits[2] = (brk << 4) | 2 | EA; /* Length, Break, EA */ len++; - - modembits[0] = len << 1 | EA; /* Data bytes */ - modembits[1] = dlci->addr << 2 | 3; /* DLCI, EA, 1 */ - modembits[2] = gsm_encode_modem(dlci) << 1 | EA; - if (brk) - modembits[3] = brk << 4 | 2 | EA; /* Valid, EA */ - ctrl = gsm_control_send(dlci->gsm, CMD_MSC, modembits, len + 1); + } + ctrl = gsm_control_send(dlci->gsm, CMD_MSC, modembits, len); if (ctrl == NULL) return -ENOMEM; return gsm_control_wait(dlci->gsm, ctrl);
