n_gsm: added interlocking for gsm_data_lock for certain code paths

There were some locking holes in the management of the MUX's
message queue for 2 code paths:
1) gsmld_write_wakeup
2) receipt of CMD_FCON flow-control message
In both cases gsm_data_kick is called w/o locking so it can collide
with other other instances of gsm_data_kick (pulling messages tx_tail)
or potentially other instances of __gsm_data_queu (adding messages to tx_head)

Changed to take the tx_lock in these 2 cases

Signed-off-by: Russ Gorby <russ.gorby@intel.com>
Tested-by: Yin, Fengwei <fengwei.yin@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Riding School <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 5f68f2a70c5c..0d93e51cb23d 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1205,6 +1205,8 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
                                                         u8 *data, int clen)
 {
         u8 buf[1];
+        unsigned long flags;
+
         switch (command) {
         case CMD_CLD: {
                 struct gsm_dlci *dlci = gsm->dlci[0];
@@ -1225,7 +1227,9 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
                 gsm->constipated = 0;
                 gsm_control_reply(gsm, CMD_FCON, NULL, 0);
                 /* Kick the link in case it is idling */
+                spin_lock_irqsave(&gsm->tx_lock, flags);
                 gsm_data_kick(gsm);
+                spin_unlock_irqrestore(&gsm->tx_lock, flags);
                 break;
         case CMD_FCOFF:
                 /* Modem wants us to STFU */
@@ -2392,12 +2396,12 @@ static void gsmld_write_wakeup(struct tty_struct *tty)
 
         /* Queue poll */
         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+        spin_lock_irqsave(&gsm->tx_lock, flags);
         gsm_data_kick(gsm);
         if (gsm->tx_bytes < TX_THRESH_LO) {
-                spin_lock_irqsave(&gsm->tx_lock, flags);
                 gsm_dlci_data_sweep(gsm);
-                spin_unlock_irqrestore(&gsm->tx_lock, flags);
         }
+        spin_unlock_irqrestore(&gsm->tx_lock, flags);
 }
 
 /**