pcmcia: synclink_cs: fix potential tty NULL dereference

tty_port_tty_get() can return NULL after port hangup that may happen anytime.
The patch adds checks that tty_port_tty_get() returns nonNULL around places
where tty is actually used.

I have no actual hardware to test the patch, so I have updated rx side
processing from common sense only.

v2: rx handling updated according Alan Cox feedback.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/char/pcmcia/synclink_cs.c b/drivers/char/pcmcia/synclink_cs.c
index 0a484b4..a6b8dde 100644 (file)
--- a/drivers/char/pcmcia/synclink_cs.c
+++ b/drivers/char/pcmcia/synclink_cs.c
@@ -891,6 +891,14 @@ static void rx_ready_async(MGSLPC_INFO *info, int tcd, struct tty_struct *tty)
        int work = 0;
        struct mgsl_icount *icount = &info->icount;
 
+       if (!tty) {
+               /* tty is not available anymore */
+               issue_command(info, CHA, CMD_RXRESET);
+               if (debug_level >= DEBUG_LEVEL_ISR)
+                       printk("%s(%d):rx_ready_async(tty=NULL)\n",__FILE__,__LINE__);
+               return;
+       }
+
        if (tcd) {
                /* early termination, get FIFO count from RBCL register */
                fifo_count = (unsigned char)(read_reg(info, CHA+RBCL) & 0x1f);
@@ -980,7 +988,7 @@ static void tx_done(MGSLPC_INFO *info, struct tty_struct *tty)
        else
 #endif
        {
-               if (tty->stopped || tty->hw_stopped) {
+               if (tty && (tty->stopped || tty->hw_stopped)) {
                        tx_stop(info);
                        return;
                }
@@ -1000,7 +1008,7 @@ static void tx_ready(MGSLPC_INFO *info, struct tty_struct *tty)
                if (!info->tx_active)
                        return;
        } else {
-               if (tty->stopped || tty->hw_stopped) {
+               if (tty && (tty->stopped || tty->hw_stopped)) {
                        tx_stop(info);
                        return;
                }
@@ -1050,13 +1058,12 @@ static void cts_change(MGSLPC_INFO *info, struct tty_struct *tty)
        wake_up_interruptible(&info->status_event_wait_q);
        wake_up_interruptible(&info->event_wait_q);
 
-       if (info->port.flags & ASYNC_CTS_FLOW) {
+       if (tty && (info->port.flags & ASYNC_CTS_FLOW)) {
                if (tty->hw_stopped) {
                        if (info->serial_signals & SerialSignal_CTS) {
                                if (debug_level >= DEBUG_LEVEL_ISR)
                                        printk("CTS tx start...");
-                               if (tty)
-                                       tty->hw_stopped = 0;
+                               tty->hw_stopped = 0;
                                tx_start(info, tty);
                                info->pending_bh |= BH_TRANSMIT;
                                return;
@@ -1065,8 +1072,7 @@ static void cts_change(MGSLPC_INFO *info, struct tty_struct *tty)
                        if (!(info->serial_signals & SerialSignal_CTS)) {
                                if (debug_level >= DEBUG_LEVEL_ISR)
                                        printk("CTS tx stop...");
-                               if (tty)
-                                       tty->hw_stopped = 1;
+                               tty->hw_stopped = 1;
                                tx_stop(info);
                        }
                }