[3.5.y.z extended stable] Patch "tty: n_gsm: Fix for modems with brk in modem status control" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    tty: n_gsm: Fix for modems with brk in modem status control

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From d08bd3475de7b5d444fa3628c6b58fc378aefbe6 Mon Sep 17 00:00:00 2001
From: Lars Poeschel <poeschel at lemonage.de>
Date: Tue, 7 Jan 2014 13:34:37 +0100
Subject: tty: n_gsm: Fix for modems with brk in modem status control

commit 3ac06b905655b3ef2fd2196bab36e4587e1e4e4f upstream.

3GPP TS 07.10 states in section 5.4.6.3.7:
"The length byte contains the value 2 or 3 ... depending on the break
signal." The break byte is optional and if it is sent, the length is
3. In fact the driver was not able to work with modems that send this
break byte in their modem status control message. If the modem just
sends the break byte if it is really set, then weird things might
happen.
The code for deconding the modem status to the internal linux
presentation in gsm_process_modem has already a big comment about
this 2 or 3 byte length thing and it is already able to decode the
brk, but the code calling the gsm_process_modem function in
gsm_control_modem does not encode it and hand it over the right way.
This patch fixes this.
Without this fix if the modem sends the brk byte in it's modem status
control message the driver will hang when opening a muxed channel.

Signed-off-by: Lars Poeschel <poeschel at lemonage.de>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/tty/n_gsm.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 4a418e4..acc0eab 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1091,6 +1091,7 @@ static void gsm_control_modem(struct gsm_mux *gsm, u8 *data, int clen)
 {
 	unsigned int addr = 0;
 	unsigned int modem = 0;
+	unsigned int brk = 0;
 	struct gsm_dlci *dlci;
 	int len = clen;
 	u8 *dp = data;
@@ -1117,6 +1118,16 @@ static void gsm_control_modem(struct gsm_mux *gsm, u8 *data, int clen)
 		if (len == 0)
 			return;
 	}
+	len--;
+	if (len > 0) {
+		while (gsm_read_ea(&brk, *dp++) == 0) {
+			len--;
+			if (len == 0)
+				return;
+		}
+		modem <<= 7;
+		modem |= (brk & 0x7f);
+	}
 	tty = tty_port_tty_get(&dlci->port);
 	gsm_process_modem(tty, dlci, modem, clen);
 	if (tty) {
--
1.9.0